text: // Copyright 2016 the V8 project authors. All rights reserved.
  // Use of this source code is governed by a BSD-style license that can be
  // found in the LICENSE file.
  
  // Used for encoding f32 and double constants to bits.
  let byte_view = new Uint8Array(8);
  let data_view = new DataView(byte_view.buffer);
  
  // The bytes function receives one of
  //  - several arguments, each of which is either a number or a string of length
  //    1; if it's a string, the charcode of the contained character is used.
  //  - a single array argument containing the actual arguments
  //  - a single string; the returned buffer will contain the char codes of all
  //    contained characters.
  function bytes(...input) {
    if (input.length == 1 && typeof input[0] == 'array') input = input[0];
    if (input.length == 1 && typeof input[0] == 'string') {
      let len = input[0].length;
      let view = new Uint8Array(len);
      for (let i = 0; i < len; i++) view[i] = input[0].charCodeAt(i);
      return view.buffer;
    }
    let view = new Uint8Array(input.length);
    for (let i = 0; i < input.length; i++) {
      let val = input[i];
      if (typeof val == 'string') {
        if (val.length != 1) {
          throw new Error('string inputs must have length 1');
        }
        val = val.charCodeAt(0);
      }
      view[i] = val | 0;
    }
    return view.buffer;
  }
  
  // Header declaration constants
  var kWasmH0 = 0;
  var kWasmH1 = 0x61;
  var kWasmH2 = 0x73;
  var kWasmH3 = 0x6d;
  
  var kWasmV0 = 0x1;
  var kWasmV1 = 0;
  var kWasmV2 = 0;
  var kWasmV3 = 0;
  
  var kHeaderSize = 8;
  var kPageSize = 65536;
  var kSpecMaxPages = 65536;
  var kMaxVarInt32Size = 5;
  var kMaxVarInt64Size = 10;
  
  let kDeclNoLocals = 0;
  
  // Section declaration constants
  let kUnknownSectionCode = 0;
  let kTypeSectionCode = 1;        // Function signature declarations
  let kImportSectionCode = 2;      // Import declarations
  let kFunctionSectionCode = 3;    // Function declarations
  let kTableSectionCode = 4;       // Indirect function table and other tables
  let kMemorySectionCode = 5;      // Memory attributes
  let kGlobalSectionCode = 6;      // Global declarations
  let kExportSectionCode = 7;      // Exports
  let kStartSectionCode = 8;       // Start function declaration
  let kElementSectionCode = 9;     // Elements section
  let kCodeSectionCode = 10;       // Function code
  let kDataSectionCode = 11;       // Data segments
  let kDataCountSectionCode = 12;  // Data segment count (between Element & Code)
  let kExceptionSectionCode = 13;  // Exception section (between Memory & Global)
  
  // Name section types
  let kModuleNameCode = 0;
  let kFunctionNamesCode = 1;
  let kLocalNamesCode = 2;
  
  let kWasmFunctionTypeForm = 0x60;
  let kWasmStructTypeForm = 0x5f;
  let kWasmArrayTypeForm = 0x5e;
  
  let kLimitsNoMaximum = 0x00;
  let kLimitsWithMaximum = 0x01;
  let kLimitsSharedNoMaximum = 0x02;
  let kLimitsSharedWithMaximum = 0x03;
  let kLimitsMemory64NoMaximum = 0x04;
  let kLimitsMemory64WithMaximum = 0x05;
  
  // Segment flags
  let kActiveNoIndex = 0;
  let kPassive = 1;
  let kActiveWithIndex = 2;
  let kDeclarative = 3;
  let kPassiveWithElements = 5;
  let kDeclarativeWithElements = 7;
  
  // Function declaration flags
  let kDeclFunctionName = 0x01;
  let kDeclFunctionImport = 0x02;
  let kDeclFunctionLocals = 0x04;
  let kDeclFunctionExport = 0x08;
  
  // Value types and related
  let kWasmVoid = 0x40;
  let kWasmI32 = 0x7f;
  let kWasmI64 = 0x7e;
  let kWasmF32 = 0x7d;
  let kWasmF64 = 0x7c;
  let kWasmS128 = 0x7b;
  let kWasmI8 = 0x7a;
  let kWasmI16 = 0x79;
  let kWasmFuncRef = 0x70;
  let kWasmAnyFunc = kWasmFuncRef;  // Alias named as in the JS API spec
  let kWasmExternRef = 0x6f;
  let kWasmAnyRef = 0x6e;
  let kWasmEqRef = 0x6d;
  let kWasmOptRef = 0x6c;
  let kWasmRef = 0x6b;
  function wasmOptRefType(index) {
    return {opcode: kWasmOptRef, index: index};
  }
  function wasmRefType(index) {
    return {opcode: kWasmRef, index: index};
  }
  let kWasmI31Ref = 0x6a;
  let kWasmRttWithDepth = 0x69;
  function wasmRtt(index, depth) {
    return {opcode: kWasmRttWithDepth, index: index, depth: depth};
  }
  let kWasmRtt = 0x68;
  function wasmRttNoDepth(index) {
    return {opcode: kWasmRtt, index: index};
  }
  let kWasmDataRef = 0x67;
  
  let kExternalFunction = 0;
  let kExternalTable = 1;
  let kExternalMemory = 2;
  let kExternalGlobal = 3;
  let kExternalException = 4;
  
  let kTableZero = 0;
  let kMemoryZero = 0;
  let kSegmentZero = 0;
  
  let kExceptionAttribute = 0;
  
  // Useful signatures
  let kSig_i_i = makeSig([kWasmI32], [kWasmI32]);
  let kSig_l_l = makeSig([kWasmI64], [kWasmI64]);
  let kSig_i_l = makeSig([kWasmI64], [kWasmI32]);
  let kSig_i_ii = makeSig([kWasmI32, kWasmI32], [kWasmI32]);
  let kSig_i_iii = makeSig([kWasmI32, kWasmI32, kWasmI32], [kWasmI32]);
  let kSig_v_iiii = makeSig([kWasmI32, kWasmI32, kWasmI32, kWasmI32], []);
  let kSig_f_ff = makeSig([kWasmF32, kWasmF32], [kWasmF32]);
  let kSig_d_dd = makeSig([kWasmF64, kWasmF64], [kWasmF64]);
  let kSig_l_ll = makeSig([kWasmI64, kWasmI64], [kWasmI64]);
  let kSig_i_dd = makeSig([kWasmF64, kWasmF64], [kWasmI32]);
  let kSig_v_v = makeSig([], []);
  let kSig_i_v = makeSig([], [kWasmI32]);
  let kSig_l_v = makeSig([], [kWasmI64]);
  let kSig_f_v = makeSig([], [kWasmF32]);
  let kSig_d_v = makeSig([], [kWasmF64]);
  let kSig_v_i = makeSig([kWasmI32], []);
  let kSig_v_ii = makeSig([kWasmI32, kWasmI32], []);
  let kSig_v_iii = makeSig([kWasmI32, kWasmI32, kWasmI32], []);
  let kSig_v_l = makeSig([kWasmI64], []);
  let kSig_v_d = makeSig([kWasmF64], []);
  let kSig_v_dd = makeSig([kWasmF64, kWasmF64], []);
  let kSig_v_ddi = makeSig([kWasmF64, kWasmF64, kWasmI32], []);
  let kSig_ii_v = makeSig([], [kWasmI32, kWasmI32]);
  let kSig_iii_v = makeSig([], [kWasmI32, kWasmI32, kWasmI32]);
  let kSig_ii_i = makeSig([kWasmI32], [kWasmI32, kWasmI32]);
  let kSig_iii_i = makeSig([kWasmI32], [kWasmI32, kWasmI32, kWasmI32]);
  let kSig_ii_ii = makeSig([kWasmI32, kWasmI32], [kWasmI32, kWasmI32]);
  let kSig_iii_ii = makeSig([kWasmI32, kWasmI32], [kWasmI32, kWasmI32, kWasmI32]);
  
  let kSig_v_f = makeSig([kWasmF32], []);
  let kSig_f_f = makeSig([kWasmF32], [kWasmF32]);
  let kSig_f_d = makeSig([kWasmF64], [kWasmF32]);
  let kSig_d_d = makeSig([kWasmF64], [kWasmF64]);
  let kSig_r_r = makeSig([kWasmExternRef], [kWasmExternRef]);
  let kSig_a_a = makeSig([kWasmAnyFunc], [kWasmAnyFunc]);
  let kSig_i_r = makeSig([kWasmExternRef], [kWasmI32]);
  let kSig_v_r = makeSig([kWasmExternRef], []);
  let kSig_v_a = makeSig([kWasmAnyFunc], []);
  let kSig_v_rr = makeSig([kWasmExternRef, kWasmExternRef], []);
  let kSig_v_aa = makeSig([kWasmAnyFunc, kWasmAnyFunc], []);
  let kSig_r_v = makeSig([], [kWasmExternRef]);
  let kSig_a_v = makeSig([], [kWasmAnyFunc]);
  let kSig_a_i = makeSig([kWasmI32], [kWasmAnyFunc]);
  let kSig_s_i = makeSig([kWasmI32], [kWasmS128]);
  let kSig_i_s = makeSig([kWasmS128], [kWasmI32]);
  
  function makeSig(params, results) {
    return {params: params, results: results};
  }
  
  function makeSig_v_x(x) {
    return makeSig([x], []);
  }
  
  function makeSig_v_xx(x) {
    return makeSig([x, x], []);
  }
  
  function makeSig_r_v(r) {
    return makeSig([], [r]);
  }
  
  function makeSig_r_x(r, x) {
    return makeSig([x], [r]);
  }
  
  function makeSig_r_xx(r, x) {
    return makeSig([x, x], [r]);
  }
  
  // Opcodes
  const kWasmOpcodes = {
    'Unreachable': 0x00,
    'Nop': 0x01,
    'Block': 0x02,
    'Loop': 0x03,
    'If': 0x04,
    'Else': 0x05,
    'Try': 0x06,
    'Catch': 0x07,
    'Throw': 0x08,
    'Rethrow': 0x09,
    'CatchAll': 0x19,
    'Unwind': 0x0a,
    'End': 0x0b,
    'Br': 0x0c,
    'BrIf': 0x0d,
    'BrTable': 0x0e,
    'Return': 0x0f,
    'CallFunction': 0x10,
    'CallIndirect': 0x11,
    'ReturnCall': 0x12,
    'ReturnCallIndirect': 0x13,
    'CallRef': 0x14,
    'ReturnCallRef': 0x15,
    'Let': 0x17,
    'Delegate': 0x18,
    'Drop': 0x1a,
    'Select': 0x1b,
    'SelectWithType': 0x1c,
    'LocalGet': 0x20,
    'LocalSet': 0x21,
    'LocalTee': 0x22,
    'GlobalGet': 0x23,
    'GlobalSet': 0x24,
    'TableGet': 0x25,
    'TableSet': 0x26,
    'I32LoadMem': 0x28,
    'I64LoadMem': 0x29,
    'F32LoadMem': 0x2a,
    'F64LoadMem': 0x2b,
    'I32LoadMem8S': 0x2c,
    'I32LoadMem8U': 0x2d,
    'I32LoadMem16S': 0x2e,
    'I32LoadMem16U': 0x2f,
    'I64LoadMem8S': 0x30,
    'I64LoadMem8U': 0x31,
    'I64LoadMem16S': 0x32,
    'I64LoadMem16U': 0x33,
    'I64LoadMem32S': 0x34,
    'I64LoadMem32U': 0x35,
    'I32StoreMem': 0x36,
    'I64StoreMem': 0x37,
    'F32StoreMem': 0x38,
    'F64StoreMem': 0x39,
    'I32StoreMem8': 0x3a,
    'I32StoreMem16': 0x3b,
    'I64StoreMem8': 0x3c,
    'I64StoreMem16': 0x3d,
    'I64StoreMem32': 0x3e,
    'MemorySize': 0x3f,
    'MemoryGrow': 0x40,
    'I32Const': 0x41,
    'I64Const': 0x42,
    'F32Const': 0x43,
    'F64Const': 0x44,
    'I32Eqz': 0x45,
    'I32Eq': 0x46,
    'I32Ne': 0x47,
    'I32LtS': 0x48,
    'I32LtU': 0x49,
    'I32GtS': 0x4a,
    'I32GtU': 0x4b,
    'I32LeS': 0x4c,
    'I32LeU': 0x4d,
    'I32GeS': 0x4e,
    'I32GeU': 0x4f,
    'I64Eqz': 0x50,
    'I64Eq': 0x51,
    'I64Ne': 0x52,
    'I64LtS': 0x53,
    'I64LtU': 0x54,
    'I64GtS': 0x55,
    'I64GtU': 0x56,
    'I64LeS': 0x57,
    'I64LeU': 0x58,
    'I64GeS': 0x59,
    'I64GeU': 0x5a,
    'F32Eq': 0x5b,
    'F32Ne': 0x5c,
    'F32Lt': 0x5d,
    'F32Gt': 0x5e,
    'F32Le': 0x5f,
    'F32Ge': 0x60,
    'F64Eq': 0x61,
    'F64Ne': 0x62,
    'F64Lt': 0x63,
    'F64Gt': 0x64,
    'F64Le': 0x65,
    'F64Ge': 0x66,
    'I32Clz': 0x67,
    'I32Ctz': 0x68,
    'I32Popcnt': 0x69,
    'I32Add': 0x6a,
    'I32Sub': 0x6b,
    'I32Mul': 0x6c,
    'I32DivS': 0x6d,
    'I32DivU': 0x6e,
    'I32RemS': 0x6f,
    'I32RemU': 0x70,
    'I32And': 0x71,
    'I32Ior': 0x72,
    'I32Xor': 0x73,
    'I32Shl': 0x74,
    'I32ShrS': 0x75,
    'I32ShrU': 0x76,
    'I32Rol': 0x77,
    'I32Ror': 0x78,
    'I64Clz': 0x79,
    'I64Ctz': 0x7a,
    'I64Popcnt': 0x7b,
    'I64Add': 0x7c,
    'I64Sub': 0x7d,
    'I64Mul': 0x7e,
    'I64DivS': 0x7f,
    'I64DivU': 0x80,
    'I64RemS': 0x81,
    'I64RemU': 0x82,
    'I64And': 0x83,
    'I64Ior': 0x84,
    'I64Xor': 0x85,
    'I64Shl': 0x86,
    'I64ShrS': 0x87,
    'I64ShrU': 0x88,
    'I64Rol': 0x89,
    'I64Ror': 0x8a,
    'F32Abs': 0x8b,
    'F32Neg': 0x8c,
    'F32Ceil': 0x8d,
    'F32Floor': 0x8e,
    'F32Trunc': 0x8f,
    'F32NearestInt': 0x90,
    'F32Sqrt': 0x91,
    'F32Add': 0x92,
    'F32Sub': 0x93,
    'F32Mul': 0x94,
    'F32Div': 0x95,
    'F32Min': 0x96,
    'F32Max': 0x97,
    'F32CopySign': 0x98,
    'F64Abs': 0x99,
    'F64Neg': 0x9a,
    'F64Ceil': 0x9b,
    'F64Floor': 0x9c,
    'F64Trunc': 0x9d,
    'F64NearestInt': 0x9e,
    'F64Sqrt': 0x9f,
    'F64Add': 0xa0,
    'F64Sub': 0xa1,
    'F64Mul': 0xa2,
    'F64Div': 0xa3,
    'F64Min': 0xa4,
    'F64Max': 0xa5,
    'F64CopySign': 0xa6,
    'I32ConvertI64': 0xa7,
    'I32SConvertF32': 0xa8,
    'I32UConvertF32': 0xa9,
    'I32SConvertF64': 0xaa,
    'I32UConvertF64': 0xab,
    'I64SConvertI32': 0xac,
    'I64UConvertI32': 0xad,
    'I64SConvertF32': 0xae,
    'I64UConvertF32': 0xaf,
    'I64SConvertF64': 0xb0,
    'I64UConvertF64': 0xb1,
    'F32SConvertI32': 0xb2,
    'F32UConvertI32': 0xb3,
    'F32SConvertI64': 0xb4,
    'F32UConvertI64': 0xb5,
    'F32ConvertF64': 0xb6,
    'F64SConvertI32': 0xb7,
    'F64UConvertI32': 0xb8,
    'F64SConvertI64': 0xb9,
    'F64UConvertI64': 0xba,
    'F64ConvertF32': 0xbb,
    'I32ReinterpretF32': 0xbc,
    'I64ReinterpretF64': 0xbd,
    'F32ReinterpretI32': 0xbe,
    'F64ReinterpretI64': 0xbf,
    'I32SExtendI8': 0xc0,
    'I32SExtendI16': 0xc1,
    'I64SExtendI8': 0xc2,
    'I64SExtendI16': 0xc3,
    'I64SExtendI32': 0xc4,
    'RefNull': 0xd0,
    'RefIsNull': 0xd1,
    'RefFunc': 0xd2,
    'RefAsNonNull': 0xd3,
    'BrOnNull': 0xd4,
    'RefEq': 0xd5,
  };
  
  function defineWasmOpcode(name, value) {
    if (globalThis.kWasmOpcodeNames === undefined) {
      globalThis.kWasmOpcodeNames = {};
    }
    Object.defineProperty(globalThis, name, {value: value});
    if (globalThis.kWasmOpcodeNames[value] !== undefined) {
      throw new Error(`Duplicate wasm opcode: ${value}. Previous name: ${
          globalThis.kWasmOpcodeNames[value]}, new name: ${name}`);
    }
    globalThis.kWasmOpcodeNames[value] = name;
  }
  for (let name in kWasmOpcodes) {
    defineWasmOpcode(`kExpr${name}`, kWasmOpcodes[name]);
  }
  
  // Prefix opcodes
  const kPrefixOpcodes = {
    'GC': 0xfb,
    'Numeric': 0xfc,
    'Simd': 0xfd,
    'Atomic': 0xfe
  };
  for (let prefix in kPrefixOpcodes) {
    defineWasmOpcode(`k${prefix}Prefix`, kPrefixOpcodes[prefix]);
  }
  
  // GC opcodes
  let kExprStructNewWithRtt = 0x01;
  let kExprStructNewDefault = 0x02;
  let kExprStructGet = 0x03;
  let kExprStructGetS = 0x04;
  let kExprStructGetU = 0x05;
  let kExprStructSet = 0x06;
  let kExprArrayNewWithRtt = 0x11;
  let kExprArrayNewDefault = 0x12;
  let kExprArrayGet = 0x13;
  let kExprArrayGetS = 0x14;
  let kExprArrayGetU = 0x15;
  let kExprArraySet = 0x16;
  let kExprArrayLen = 0x17;
  let kExprI31New = 0x20;
  let kExprI31GetS = 0x21;
  let kExprI31GetU = 0x22;
  let kExprRttCanon = 0x30;
  let kExprRttSub = 0x31;
  let kExprRefTest = 0x40;
  let kExprRefCast = 0x41;
  let kExprBrOnCast = 0x42;
  let kExprRefIsFunc = 0x50;
  let kExprRefIsData = 0x51;
  let kExprRefIsI31 = 0x52;
  let kExprRefAsFunc = 0x58;
  let kExprRefAsData = 0x59;
  let kExprRefAsI31 = 0x5a;
  let kExprBrOnFunc = 0x60;
  let kExprBrOnData = 0x61;
  let kExprBrOnI31 = 0x62;
  
  // Numeric opcodes.
  let kExprI32SConvertSatF32 = 0x00;
  let kExprI32UConvertSatF32 = 0x01;
  let kExprI32SConvertSatF64 = 0x02;
  let kExprI32UConvertSatF64 = 0x03;
  let kExprI64SConvertSatF32 = 0x04;
  let kExprI64UConvertSatF32 = 0x05;
  let kExprI64SConvertSatF64 = 0x06;
  let kExprI64UConvertSatF64 = 0x07;
  let kExprMemoryInit = 0x08;
  let kExprDataDrop = 0x09;
  let kExprMemoryCopy = 0x0a;
  let kExprMemoryFill = 0x0b;
  let kExprTableInit = 0x0c;
  let kExprElemDrop = 0x0d;
  let kExprTableCopy = 0x0e;
  let kExprTableGrow = 0x0f;
  let kExprTableSize = 0x10;
  let kExprTableFill = 0x11;
  
  // Atomic opcodes.
  let kExprAtomicNotify = 0x00;
  let kExprI32AtomicWait = 0x01;
  let kExprI64AtomicWait = 0x02;
  let kExprI32AtomicLoad = 0x10;
  let kExprI32AtomicLoad8U = 0x12;
  let kExprI32AtomicLoad16U = 0x13;
  let kExprI32AtomicStore = 0x17;
  let kExprI32AtomicStore8U = 0x19;
  let kExprI32AtomicStore16U = 0x1a;
  let kExprI32AtomicAdd = 0x1e;
  let kExprI32AtomicAdd8U = 0x20;
  let kExprI32AtomicAdd16U = 0x21;
  let kExprI32AtomicSub = 0x25;
  let kExprI32AtomicSub8U = 0x27;
  let kExprI32AtomicSub16U = 0x28;
  let kExprI32AtomicAnd = 0x2c;
  let kExprI32AtomicAnd8U = 0x2e;
  let kExprI32AtomicAnd16U = 0x2f;
  let kExprI32AtomicOr = 0x33;
  let kExprI32AtomicOr8U = 0x35;
  let kExprI32AtomicOr16U = 0x36;
  let kExprI32AtomicXor = 0x3a;
  let kExprI32AtomicXor8U = 0x3c;
  let kExprI32AtomicXor16U = 0x3d;
  let kExprI32AtomicExchange = 0x41;
  let kExprI32AtomicExchange8U = 0x43;
  let kExprI32AtomicExchange16U = 0x44;
  let kExprI32AtomicCompareExchange = 0x48;
  let kExprI32AtomicCompareExchange8U = 0x4a;
  let kExprI32AtomicCompareExchange16U = 0x4b;
  
  let kExprI64AtomicLoad = 0x11;
  let kExprI64AtomicLoad8U = 0x14;
  let kExprI64AtomicLoad16U = 0x15;
  let kExprI64AtomicLoad32U = 0x16;
  let kExprI64AtomicStore = 0x18;
  let kExprI64AtomicStore8U = 0x1b;
  let kExprI64AtomicStore16U = 0x1c;
  let kExprI64AtomicStore32U = 0x1d;
  let kExprI64AtomicAdd = 0x1f;
  let kExprI64AtomicAdd8U = 0x22;
  let kExprI64AtomicAdd16U = 0x23;
  let kExprI64AtomicAdd32U = 0x24;
  let kExprI64AtomicSub = 0x26;
  let kExprI64AtomicSub8U = 0x29;
  let kExprI64AtomicSub16U = 0x2a;
  let kExprI64AtomicSub32U = 0x2b;
  let kExprI64AtomicAnd = 0x2d;
  let kExprI64AtomicAnd8U = 0x30;
  let kExprI64AtomicAnd16U = 0x31;
  let kExprI64AtomicAnd32U = 0x32;
  let kExprI64AtomicOr = 0x34;
  let kExprI64AtomicOr8U = 0x37;
  let kExprI64AtomicOr16U = 0x38;
  let kExprI64AtomicOr32U = 0x39;
  let kExprI64AtomicXor = 0x3b;
  let kExprI64AtomicXor8U = 0x3e;
  let kExprI64AtomicXor16U = 0x3f;
  let kExprI64AtomicXor32U = 0x40;
  let kExprI64AtomicExchange = 0x42;
  let kExprI64AtomicExchange8U = 0x45;
  let kExprI64AtomicExchange16U = 0x46;
  let kExprI64AtomicExchange32U = 0x47;
  let kExprI64AtomicCompareExchange = 0x49
  let kExprI64AtomicCompareExchange8U = 0x4c;
  let kExprI64AtomicCompareExchange16U = 0x4d;
  let kExprI64AtomicCompareExchange32U = 0x4e;
  
  // Simd opcodes.
  let kExprS128LoadMem = 0x00;
  let kExprS128Load8x8S = 0x01;
  let kExprS128Load8x8U = 0x02;
  let kExprS128Load16x4S = 0x03;
  let kExprS128Load16x4U = 0x04;
  let kExprS128Load32x2S = 0x05;
  let kExprS128Load32x2U = 0x06;
  let kExprS128Load8Splat = 0x07;
  let kExprS128Load16Splat = 0x08;
  let kExprS128Load32Splat = 0x09;
  let kExprS128Load64Splat = 0x0a;
  let kExprS128StoreMem = 0x0b;
  let kExprS128Const = 0x0c;
  let kExprI8x16Shuffle = 0x0d;
  let kExprI8x16Swizzle = 0x0e;
  
  let kExprI8x16Splat = 0x0f;
  let kExprI16x8Splat = 0x10;
  let kExprI32x4Splat = 0x11;
  let kExprI64x2Splat = 0x12;
  let kExprF32x4Splat = 0x13;
  let kExprF64x2Splat = 0x14;
  let kExprI8x16ExtractLaneS = 0x15;
  let kExprI8x16ExtractLaneU = 0x16;
  let kExprI8x16ReplaceLane = 0x17;
  let kExprI16x8ExtractLaneS = 0x18;
  let kExprI16x8ExtractLaneU = 0x19;
  let kExprI16x8ReplaceLane = 0x1a;
  let kExprI32x4ExtractLane = 0x1b;
  let kExprI32x4ReplaceLane = 0x1c;
  let kExprI64x2ExtractLane = 0x1d;
  let kExprI64x2ReplaceLane = 0x1e;
  let kExprF32x4ExtractLane = 0x1f;
  let kExprF32x4ReplaceLane = 0x20;
  let kExprF64x2ExtractLane = 0x21;
  let kExprF64x2ReplaceLane = 0x22;
  let kExprI8x16Eq = 0x23;
  let kExprI8x16Ne = 0x24;
  let kExprI8x16LtS = 0x25;
  let kExprI8x16LtU = 0x26;
  let kExprI8x16GtS = 0x27;
  let kExprI8x16GtU = 0x28;
  let kExprI8x16LeS = 0x29;
  let kExprI8x16LeU = 0x2a;
  let kExprI8x16GeS = 0x2b;
  let kExprI8x16GeU = 0x2c;
  let kExprI16x8Eq = 0x2d;
  let kExprI16x8Ne = 0x2e;
  let kExprI16x8LtS = 0x2f;
  let kExprI16x8LtU = 0x30;
  let kExprI16x8GtS = 0x31;
  let kExprI16x8GtU = 0x32;
  let kExprI16x8LeS = 0x33;
  let kExprI16x8LeU = 0x34;
  let kExprI16x8GeS = 0x35;
  let kExprI16x8GeU = 0x36;
  let kExprI32x4Eq = 0x37;
  let kExprI32x4Ne = 0x38;
  let kExprI32x4LtS = 0x39;
  let kExprI32x4LtU = 0x3a;
  let kExprI32x4GtS = 0x3b;
  let kExprI32x4GtU = 0x3c;
  let kExprI32x4LeS = 0x3d;
  let kExprI32x4LeU = 0x3e;
  let kExprI32x4GeS = 0x3f;
  let kExprI32x4GeU = 0x40;
  let kExprF32x4Eq = 0x41;
  let kExprF32x4Ne = 0x42;
  let kExprF32x4Lt = 0x43;
  let kExprF32x4Gt = 0x44;
  let kExprF32x4Le = 0x45;
  let kExprF32x4Ge = 0x46;
  let kExprF64x2Eq = 0x47;
  let kExprF64x2Ne = 0x48;
  let kExprF64x2Lt = 0x49;
  let kExprF64x2Gt = 0x4a;
  let kExprF64x2Le = 0x4b;
  let kExprF64x2Ge = 0x4c;
  let kExprS128Not = 0x4d;
  let kExprS128And = 0x4e;
  let kExprS128AndNot = 0x4f;
  let kExprS128Or = 0x50;
  let kExprS128Xor = 0x51;
  let kExprS128Select = 0x52;
  let kExprV128AnyTrue = 0x53;
  let kExprS128Load8Lane = 0x54;
  let kExprS128Load16Lane = 0x55;
  let kExprS128Load32Lane = 0x56;
  let kExprS128Load64Lane = 0x57;
  let kExprS128Store8Lane = 0x58;
  let kExprS128Store16Lane = 0x59;
  let kExprS128Store32Lane = 0x5a;
  let kExprS128Store64Lane = 0x5b;
  let kExprS128Load32Zero = 0x5c;
  let kExprS128Load64Zero = 0x5d;
  let kExprF32x4DemoteF64x2Zero = 0x5e;
  let kExprF64x2PromoteLowF32x4 = 0x5f;
  let kExprI8x16Abs = 0x60;
  let kExprI8x16Neg = 0x61;
  let kExprI8x16Popcnt = 0x62;
  let kExprI8x16AllTrue = 0x63;
  let kExprI8x16BitMask = 0x64;
  let kExprI8x16SConvertI16x8 = 0x65;
  let kExprI8x16UConvertI16x8 = 0x66;
  let kExprF32x4Ceil = 0x67;
  let kExprF32x4Floor = 0x68;
  let kExprF32x4Trunc = 0x69;
  let kExprF32x4NearestInt = 0x6a;
  let kExprI8x16Shl = 0x6b;
  let kExprI8x16ShrS = 0x6c;
  let kExprI8x16ShrU = 0x6d;
  let kExprI8x16Add = 0x6e;
  let kExprI8x16AddSatS = 0x6f;
  let kExprI8x16AddSatU = 0x70;
  let kExprI8x16Sub = 0x71;
  let kExprI8x16SubSatS = 0x72;
  let kExprI8x16SubSatU = 0x73;
  let kExprF64x2Ceil = 0x74;
  let kExprF64x2Floor = 0x75;
  let kExprI8x16MinS = 0x76;
  let kExprI8x16MinU = 0x77;
  let kExprI8x16MaxS = 0x78;
  let kExprI8x16MaxU = 0x79;
  let kExprF64x2Trunc = 0x7a;
  let kExprI8x16RoundingAverageU = 0x7b;
  let kExprI16x8ExtAddPairwiseI8x16S = 0x7c;
  let kExprI16x8ExtAddPairwiseI8x16U = 0x7d;
  let kExprI32x4ExtAddPairwiseI16x8S = 0x7e;
  let kExprI32x4ExtAddPairwiseI16x8U = 0x7f;
  let kExprI16x8Abs = 0x80;
  let kExprI16x8Neg = 0x81;
  let kExprI16x8Q15MulRSatS = 0x82;
  let kExprI16x8AllTrue = 0x83;
  let kExprI16x8BitMask = 0x84;
  let kExprI16x8SConvertI32x4 = 0x85;
  let kExprI16x8UConvertI32x4 = 0x86;
  let kExprI16x8SConvertI8x16Low = 0x87;
  let kExprI16x8SConvertI8x16High = 0x88;
  let kExprI16x8UConvertI8x16Low = 0x89;
  let kExprI16x8UConvertI8x16High = 0x8a;
  let kExprI16x8Shl = 0x8b;
  let kExprI16x8ShrS = 0x8c;
  let kExprI16x8ShrU = 0x8d;
  let kExprI16x8Add = 0x8e;
  let kExprI16x8AddSatS = 0x8f;
  let kExprI16x8AddSatU = 0x90;
  let kExprI16x8Sub = 0x91;
  let kExprI16x8SubSatS = 0x92;
  let kExprI16x8SubSatU = 0x93;
  let kExprF64x2NearestInt = 0x94;
  let kExprI16x8Mul = 0x95;
  let kExprI16x8MinS = 0x96;
  let kExprI16x8MinU = 0x97;
  let kExprI16x8MaxS = 0x98;
  let kExprI16x8MaxU = 0x99;
  let kExprI16x8RoundingAverageU = 0x9b;
  let kExprI16x8ExtMulLowI8x16S = 0x9c;
  let kExprI16x8ExtMulHighI8x16S = 0x9d;
  let kExprI16x8ExtMulLowI8x16U = 0x9e;
  let kExprI16x8ExtMulHighI8x16U = 0x9f;
  let kExprI32x4Abs = 0xa0;
  let kExprI32x4Neg = 0xa1;
  let kExprI32x4AllTrue = 0xa3;
  let kExprI32x4BitMask = 0xa4;
  let kExprI32x4SConvertI16x8Low = 0xa7;
  let kExprI32x4SConvertI16x8High = 0xa8;
  let kExprI32x4UConvertI16x8Low = 0xa9;
  let kExprI32x4UConvertI16x8High = 0xaa;
  let kExprI32x4Shl = 0xab;
  let kExprI32x4ShrS = 0xac;
  let kExprI32x4ShrU = 0xad;
  let kExprI32x4Add = 0xae;
  let kExprI32x4Sub = 0xb1;
  let kExprI32x4Mul = 0xb5;
  let kExprI32x4MinS = 0xb6;
  let kExprI32x4MinU = 0xb7;
  let kExprI32x4MaxS = 0xb8;
  let kExprI32x4MaxU = 0xb9;
  let kExprI32x4DotI16x8S = 0xba;
  let kExprI32x4ExtMulLowI16x8S = 0xbc;
  let kExprI32x4ExtMulHighI16x8S = 0xbd;
  let kExprI32x4ExtMulLowI16x8U = 0xbe;
  let kExprI32x4ExtMulHighI16x8U = 0xbf;
  let kExprI64x2Abs = 0xc0;
  let kExprI64x2Neg = 0xc1;
  let kExprI64x2AllTrue = 0xc3;
  let kExprI64x2BitMask = 0xc4;
  let kExprI64x2SConvertI32x4Low = 0xc7;
  let kExprI64x2SConvertI32x4High = 0xc8;
  let kExprI64x2UConvertI32x4Low = 0xc9;
  let kExprI64x2UConvertI32x4High = 0xca;
  let kExprI64x2Shl = 0xcb;
  let kExprI64x2ShrS = 0xcc;
  let kExprI64x2ShrU = 0xcd;
  let kExprI64x2Add = 0xce;
  let kExprI64x2Sub = 0xd1;
  let kExprI64x2Mul = 0xd5;
  let kExprI64x2Eq = 0xd6;
  let kExprI64x2Ne = 0xd7;
  let kExprI64x2LtS = 0xd8;
  let kExprI64x2GtS = 0xd9;
  let kExprI64x2LeS = 0xda;
  let kExprI64x2GeS = 0xdb;
  let kExprI64x2ExtMulLowI32x4S = 0xdc;
  let kExprI64x2ExtMulHighI32x4S = 0xdd;
  let kExprI64x2ExtMulLowI32x4U = 0xde;
  let kExprI64x2ExtMulHighI32x4U = 0xdf;
  let kExprF32x4Abs = 0xe0;
  let kExprF32x4Neg = 0xe1;
  let kExprF32x4Sqrt = 0xe3;
  let kExprF32x4Add = 0xe4;
  let kExprF32x4Sub = 0xe5;
  let kExprF32x4Mul = 0xe6;
  let kExprF32x4Div = 0xe7;
  let kExprF32x4Min = 0xe8;
  let kExprF32x4Max = 0xe9;
  let kExprF32x4Pmin = 0xea;
  let kExprF32x4Pmax = 0xeb;
  let kExprF64x2Abs = 0xec;
  let kExprF64x2Neg = 0xed;
  let kExprF64x2Sqrt = 0xef;
  let kExprF64x2Add = 0xf0;
  let kExprF64x2Sub = 0xf1;
  let kExprF64x2Mul = 0xf2;
  let kExprF64x2Div = 0xf3;
  let kExprF64x2Min = 0xf4;
  let kExprF64x2Max = 0xf5;
  let kExprF64x2Pmin = 0xf6;
  let kExprF64x2Pmax = 0xf7;
  let kExprI32x4SConvertF32x4 = 0xf8;
  let kExprI32x4UConvertF32x4 = 0xf9;
  let kExprF32x4SConvertI32x4 = 0xfa;
  let kExprF32x4UConvertI32x4 = 0xfb;
  let kExprI32x4TruncSatF64x2SZero = 0xfc;
  let kExprI32x4TruncSatF64x2UZero = 0xfd;
  let kExprF64x2ConvertLowI32x4S = 0xfe;
  let kExprF64x2ConvertLowI32x4U = 0xff;
  
  // Compilation hint constants.
  let kCompilationHintStrategyDefault = 0x00;
  let kCompilationHintStrategyLazy = 0x01;
  let kCompilationHintStrategyEager = 0x02;
  let kCompilationHintStrategyLazyBaselineEagerTopTier = 0x03;
  let kCompilationHintTierDefault = 0x00;
  let kCompilationHintTierBaseline = 0x01;
  let kCompilationHintTierOptimized = 0x02;
  
  let kTrapUnreachable = 0;
  let kTrapMemOutOfBounds = 1;
  let kTrapDivByZero = 2;
  let kTrapDivUnrepresentable = 3;
  let kTrapRemByZero = 4;
  let kTrapFloatUnrepresentable = 5;
  let kTrapTableOutOfBounds = 6;
  let kTrapFuncSigMismatch = 7;
  let kTrapUnalignedAccess = 8;
  let kTrapDataSegmentDropped = 9;
  let kTrapElemSegmentDropped = 10;
  let kTrapRethrowNull = 11;
  
  let kTrapMsgs = [
    'unreachable',                                    // --
    'memory access out of bounds',                    // --
    'divide by zero',                                 // --
    'divide result unrepresentable',                  // --
    'remainder by zero',                              // --
    'float unrepresentable in integer range',         // --
    'table index is out of bounds',                   // --
    'null function or function signature mismatch',   // --
    'operation does not support unaligned accesses',  // --
    'data segment has been dropped',                  // --
    'element segment has been dropped',               // --
    'rethrowing null value'                           // --
  ];
  
  // This requires test/mjsunit/mjsunit.js.
  function assertTraps(trap, code) {
    assertThrows(code, WebAssembly.RuntimeError, kTrapMsgs[trap]);
  }
  
  class Binary {
    constructor() {
      this.length = 0;
      this.buffer = new Uint8Array(8192);
    }
  
    ensure_space(needed) {
      if (this.buffer.length - this.length >= needed) return;
      let new_capacity = this.buffer.length * 2;
      while (new_capacity - this.length < needed) new_capacity *= 2;
      let new_buffer = new Uint8Array(new_capacity);
      new_buffer.set(this.buffer);
      this.buffer = new_buffer;
    }
  
    trunc_buffer() {
      return new Uint8Array(this.buffer.buffer, 0, this.length);
    }
  
    reset() {
      this.length = 0;
    }
  
    emit_u8(val) {
      this.ensure_space(1);
      this.buffer[this.length++] = val;
    }
  
    emit_u16(val) {
      this.ensure_space(2);
      this.buffer[this.length++] = val;
      this.buffer[this.length++] = val >> 8;
    }
  
    emit_u32(val) {
      this.ensure_space(4);
      this.buffer[this.length++] = val;
      this.buffer[this.length++] = val >> 8;
      this.buffer[this.length++] = val >> 16;
      this.buffer[this.length++] = val >> 24;
    }
  
    emit_leb_u(val, max_len) {
      this.ensure_space(max_len);
      for (let i = 0; i < max_len; ++i) {
        let v = val & 0xff;
        val = val >>> 7;
        if (val == 0) {
          this.buffer[this.length++] = v;
          return;
        }
        this.buffer[this.length++] = v | 0x80;
      }
      throw new Error('Leb value exceeds maximum length of ' + max_len);
    }
  
    emit_u32v(val) {
      this.emit_leb_u(val, kMaxVarInt32Size);
    }
  
    emit_u64v(val) {
      this.emit_leb_u(val, kMaxVarInt64Size);
    }
  
    emit_bytes(data) {
      this.ensure_space(data.length);
      this.buffer.set(data, this.length);
      this.length += data.length;
    }
  
    emit_string(string) {
      // When testing illegal names, we pass a byte array directly.
      if (string instanceof Array) {
        this.emit_u32v(string.length);
        this.emit_bytes(string);
        return;
      }
  
      // This is the hacky way to convert a JavaScript string to a UTF8 encoded
      // string only containing single-byte characters.
      let string_utf8 = unescape(encodeURIComponent(string));
      this.emit_u32v(string_utf8.length);
      for (let i = 0; i < string_utf8.length; i++) {
        this.emit_u8(string_utf8.charCodeAt(i));
      }
    }
  
    emit_type(type) {
      if ((typeof type) == 'number') {
        this.emit_u8(type);
      } else {
        this.emit_u8(type.opcode);
        if ('depth' in type) this.emit_u8(type.depth);
        this.emit_u32v(type.index);
      }
    }
  
    emit_init_expr(expr) {
      switch (expr.kind) {
        case kExprGlobalGet:
          this.emit_u8(kExprGlobalGet);
          this.emit_u32v(expr.value);
          break;
        case kExprI32Const:
          this.emit_bytes(wasmI32Const(expr.value));
          break;
        case kExprI64Const:
          this.emit_bytes(wasmI64Const(expr.value));
          break;
        case kExprF32Const:
          this.emit_bytes(wasmF32Const(expr.value));
          break;
        case kExprF64Const:
          this.emit_bytes(wasmF64Const(expr.value));
          break;
        case kSimdPrefix:
          this.emit_bytes(wasmS128Const(expr.value));
          break;
        case kExprRefFunc:
          this.emit_u8(kExprRefFunc);
          this.emit_u32v(expr.value);
          break;
        case kExprRefNull:
          this.emit_u8(kExprRefNull);
          this.emit_u32v(expr.value);
          break;
      }
      this.emit_u8(kExprEnd);  // end of init expression
    }
  
    emit_header() {
      this.emit_bytes([
        kWasmH0, kWasmH1, kWasmH2, kWasmH3, kWasmV0, kWasmV1, kWasmV2, kWasmV3
      ]);
    }
  
    emit_section(section_code, content_generator) {
      // Emit section name.
      this.emit_u8(section_code);
      // Emit the section to a temporary buffer: its full length isn't know yet.
      const section = new Binary;
      content_generator(section);
      // Emit section length.
      this.emit_u32v(section.length);
      // Copy the temporary buffer.
      // Avoid spread because {section} can be huge.
      this.emit_bytes(section.trunc_buffer());
    }
  }
  
  class WasmFunctionBuilder {
    // Encoding of local names: a string corresponds to a local name,
    // a number n corresponds to n undefined names.
    constructor(module, name, type_index, arg_names) {
      this.module = module;
      this.name = name;
      this.type_index = type_index;
      this.body = [];
      this.locals = [];
      this.local_names = arg_names;
      this.body_offset = undefined;  // Not valid until module is serialized.
    }
  
    numLocalNames() {
      let num_local_names = 0;
      for (let loc_name of this.local_names) {
        if (typeof loc_name == 'string') ++num_local_names;
      }
      return num_local_names;
    }
  
    exportAs(name) {
      this.module.addExport(name, this.index);
      return this;
    }
  
    exportFunc() {
      this.exportAs(this.name);
      return this;
    }
  
    setCompilationHint(strategy, baselineTier, topTier) {
      this.module.setCompilationHint(strategy, baselineTier, topTier, this.index);
      return this;
    }
  
    addBody(body) {
      for (let b of body) {
        if (typeof b !== 'number' || (b & (~0xFF)) !== 0) {
          throw new Error(
              'invalid body (entries must be 8 bit numbers): ' + body);
        }
      }
      this.body = body.slice();
      // Automatically add the end for the function block to the body.
      this.body.push(kExprEnd);
      return this;
    }
  
    addBodyWithEnd(body) {
      this.body = body;
      return this;
    }
  
    getNumLocals() {
      let total_locals = 0;
      for (let l of this.locals) {
        total_locals += l.count
      }
      return total_locals;
    }
  
    addLocals(type, count, names) {
      this.locals.push({type: type, count: count});
      names = names || [];
      if (names.length > count) throw new Error('too many locals names given');
      this.local_names.push(...names);
      if (count > names.length) this.local_names.push(count - names.length);
      return this;
    }
  
    end() {
      return this.module;
    }
  }
  
  class WasmInitExpr {
    static I32Const(value) {
      return {kind: kExprI32Const, value: value};
    }
    static I64Const(value) {
      return {kind: kExprI64Const, value: value};
    }
    static F32Const(value) {
      return {kind: kExprF32Const, value: value};
    }
    static F64Const(value) {
      return {kind: kExprF64Const, value: value};
    }
    static S128Const(value) {
      return {kind: kSimdPrefix, value: value};
    }
    static GlobalGet(index) {
      return {kind: kExprGlobalGet, value: index};
    }
    static RefFunc(index) {
      return {kind: kExprRefFunc, value: index};
    }
    static RefNull(type) {
      return {kind: kExprRefNull, value: type};
    }
  
    static defaultFor(type) {
      switch (type) {
        case kWasmI32:
          return this.I32Const(0);
        case kWasmI64:
          return this.I64Const(0);
        case kWasmF32:
          return this.F32Const(0);
        case kWasmF64:
          return this.F64Const(0);
        case kWasmS128:
          return this.S128Const(new Array(16).fill(0));
        default:
          let heap_type = (typeof type) == 'number' ? type : type.index;
          return this.RefNull(heap_type);
      }
    }
  }
  
  class WasmGlobalBuilder {
    // {init} a pair {type, immediate}. Construct it with WasmInitExpr.
    constructor(module, type, mutable, init) {
      this.module = module;
      this.type = type;
      this.mutable = mutable;
      this.init = init;
    }
  
    exportAs(name) {
      this.module.exports.push(
          {name: name, kind: kExternalGlobal, index: this.index});
      return this;
    }
  }
  
  class WasmTableBuilder {
    constructor(module, type, initial_size, max_size, init_expr) {
      this.module = module;
      this.type = type;
      this.initial_size = initial_size;
      this.has_max = max_size !== undefined;
      this.max_size = max_size;
      this.init_expr = init_expr;
      this.has_init = init_expr !== undefined;
    }
  
    exportAs(name) {
      this.module.exports.push(
          {name: name, kind: kExternalTable, index: this.index});
      return this;
    }
  }
  
  function makeField(type, mutability) {
    if ((typeof mutability) != 'boolean') {
      throw new Error('field mutability must be boolean');
    }
    return {type: type, mutability: mutability};
  }
  
  class WasmStruct {
    constructor(fields) {
      if (!Array.isArray(fields)) {
        throw new Error('struct fields must be an array');
      }
      this.fields = fields;
    }
  }
  
  class WasmArray {
    constructor(type) {
      this.type = type;
    }
  }
  
  class WasmElemSegment {
    constructor(table, offset, type, elements, is_decl) {
      this.table = table;
      this.offset = offset;
      this.type = type;
      this.elements = elements;
      this.is_decl = is_decl;
      // Invariant checks.
      if ((table === undefined) != (offset === undefined)) {
        throw new Error("invalid element segment");
      }
      for (let elem of elements) {
        if (((typeof elem) == 'number') != (type === undefined)) {
          throw new Error("invalid element");
        }
      }
    }
  
    is_active() {
      return this.table !== undefined;
    }
  
    is_passive() {
      return this.table === undefined && !this.is_decl;
    }
  
    is_declarative() {
      return this.table === undefined && this.is_decl;
    }
  
    expressions_as_elements() {
      return this.type !== undefined;
    }
  }
  
  class WasmModuleBuilder {
    constructor() {
      this.types = [];
      this.imports = [];
      this.exports = [];
      this.globals = [];
      this.tables = [];
      this.exceptions = [];
      this.functions = [];
      this.compilation_hints = [];
      this.element_segments = [];
      this.data_segments = [];
      this.explicit = [];
      this.num_imported_funcs = 0;
      this.num_imported_globals = 0;
      this.num_imported_tables = 0;
      this.num_imported_exceptions = 0;
      return this;
    }
  
    addStart(start_index) {
      this.start_index = start_index;
      return this;
    }
  
    addMemory(min, max, exported, shared) {
      this.memory = {
        min: min,
        max: max,
        exported: exported,
        shared: shared || false,
        is_memory64: false
      };
      return this;
    }
  
    addMemory64(min, max, exported) {
      this.memory = {
        min: min,
        max: max,
        exported: exported,
        shared: false,
        is_memory64: true
      };
      return this;
    }
  
    addExplicitSection(bytes) {
      this.explicit.push(bytes);
      return this;
    }
  
    stringToBytes(name) {
      var result = new Binary();
      result.emit_u32v(name.length);
      for (var i = 0; i < name.length; i++) {
        result.emit_u8(name.charCodeAt(i));
      }
      return result.trunc_buffer()
    }
  
    createCustomSection(name, bytes) {
      name = this.stringToBytes(name);
      var section = new Binary();
      section.emit_u8(0);
      section.emit_u32v(name.length + bytes.length);
      section.emit_bytes(name);
      section.emit_bytes(bytes);
      return section.trunc_buffer();
    }
  
    addCustomSection(name, bytes) {
      this.explicit.push(this.createCustomSection(name, bytes));
    }
  
    addType(type) {
      this.types.push(type);
      var pl = type.params.length;   // should have params
      var rl = type.results.length;  // should have results
      return this.types.length - 1;
    }
  
    addStruct(fields) {
      this.types.push(new WasmStruct(fields));
      return this.types.length - 1;
    }
  
    addArray(type) {
      this.types.push(new WasmArray(type));
      return this.types.length - 1;
    }
  
    addGlobal(type, mutable, init) {
      if (init === undefined) init = WasmInitExpr.defaultFor(type);
      let glob = new WasmGlobalBuilder(this, type, mutable, init);
      glob.index = this.globals.length + this.num_imported_globals;
      this.globals.push(glob);
      return glob;
    }
  
    addTable(
        type, initial_size, max_size = undefined, init_expr = undefined) {
      if (type == kWasmI32 || type == kWasmI64 || type == kWasmF32 ||
          type == kWasmF64 || type == kWasmS128 || type == kWasmVoid) {
        throw new Error('Tables must be of a reference type');
      }
      let table = new WasmTableBuilder(
          this, type, initial_size, max_size, init_expr);
      table.index = this.tables.length + this.num_imported_tables;
      this.tables.push(table);
      return table;
    }
  
    addException(type) {
      let type_index = (typeof type) == 'number' ? type : this.addType(type);
      let except_index = this.exceptions.length + this.num_imported_exceptions;
      this.exceptions.push(type_index);
      return except_index;
    }
  
    addFunction(name, type, arg_names) {
      arg_names = arg_names || [];
      let type_index = (typeof type) == 'number' ? type : this.addType(type);
      let num_args = this.types[type_index].params.length;
      if (num_args < arg_names.length)
        throw new Error('too many arg names provided');
      if (num_args > arg_names.length)
        arg_names.push(num_args - arg_names.length);
      let func = new WasmFunctionBuilder(this, name, type_index, arg_names);
      func.index = this.functions.length + this.num_imported_funcs;
      this.functions.push(func);
      return func;
    }
  
    addImport(module, name, type) {
      if (this.functions.length != 0) {
        throw new Error('Imported functions must be declared before local ones');
      }
      let type_index = (typeof type) == 'number' ? type : this.addType(type);
      this.imports.push({
        module: module,
        name: name,
        kind: kExternalFunction,
        type_index: type_index
      });
      return this.num_imported_funcs++;
    }
  
    addImportedGlobal(module, name, type, mutable = false) {
      if (this.globals.length != 0) {
        throw new Error('Imported globals must be declared before local ones');
      }
      let o = {
        module: module,
        name: name,
        kind: kExternalGlobal,
        type: type,
        mutable: mutable
      };
      this.imports.push(o);
      return this.num_imported_globals++;
    }
  
    addImportedMemory(module, name, initial = 0, maximum, shared) {
      let o = {
        module: module,
        name: name,
        kind: kExternalMemory,
        initial: initial,
        maximum: maximum,
        shared: shared
      };
      this.imports.push(o);
      return this;
    }
  
    addImportedTable(module, name, initial, maximum, type) {
      if (this.tables.length != 0) {
        throw new Error('Imported tables must be declared before local ones');
      }
      let o = {
        module: module,
        name: name,
        kind: kExternalTable,
        initial: initial,
        maximum: maximum,
        type: type || kWasmFuncRef
      };
      this.imports.push(o);
      return this.num_imported_tables++;
    }
  
    addImportedException(module, name, type) {
      if (this.exceptions.length != 0) {
        throw new Error('Imported exceptions must be declared before local ones');
      }
      let type_index = (typeof type) == 'number' ? type : this.addType(type);
      let o = {
        module: module,
        name: name,
        kind: kExternalException,
        type_index: type_index
      };
      this.imports.push(o);
      return this.num_imported_exceptions++;
    }
  
    addExport(name, index) {
      this.exports.push({name: name, kind: kExternalFunction, index: index});
      return this;
    }
  
    addExportOfKind(name, kind, index) {
      if (index === undefined && kind != kExternalTable &&
          kind != kExternalMemory) {
        throw new Error(
            'Index for exports other than tables/memories must be provided');
      }
      if (index !== undefined && (typeof index) != 'number') {
        throw new Error('Index for exports must be a number')
      }
      this.exports.push({name: name, kind: kind, index: index});
      return this;
    }
  
    setCompilationHint(strategy, baselineTier, topTier, index) {
      this.compilation_hints[index] = {
        strategy: strategy,
        baselineTier: baselineTier,
        topTier: topTier
      };
      return this;
    }
  
    addDataSegment(addr, data, is_global = false) {
      this.data_segments.push(
          {addr: addr, data: data, is_global: is_global, is_active: true});
      return this.data_segments.length - 1;
    }
  
    addPassiveDataSegment(data) {
      this.data_segments.push({data: data, is_active: false});
      return this.data_segments.length - 1;
    }
  
    exportMemoryAs(name) {
      this.exports.push({name: name, kind: kExternalMemory, index: 0});
    }
  
    // {offset} is an initializer expression.
    // If {type} is undefined, then {elements} are function indices. Otherwise,
    // they are initializer expressions.
    addActiveElementSegment(table, offset, elements, type) {
      this.element_segments.push(
          new WasmElemSegment(table, offset, type, elements, false));
      return this.element_segments.length - 1;
    }
  
    // If {type} is undefined, then {elements} are function indices. Otherwise,
    // they are initializer expressions.
    addPassiveElementSegment(elements, type) {
      this.element_segments.push(
        new WasmElemSegment(undefined, undefined, type, elements, false));
      return this.element_segments.length - 1;
    }
  
    // If {type} is undefined, then {elements} are function indices. Otherwise,
    // they are initializer expressions.
    addDeclarativeElementSegment(elements, type) {
      this.element_segments.push(
        new WasmElemSegment(undefined, undefined, type, elements, true));
      return this.element_segments.length - 1;
    }
  
    appendToTable(array) {
      for (let n of array) {
        if (typeof n != 'number')
          throw new Error('invalid table (entries have to be numbers): ' + array);
      }
      if (this.tables.length == 0) {
        this.addTable(kWasmAnyFunc, 0);
      }
      // Adjust the table to the correct size.
      let table = this.tables[0];
      const base = table.initial_size;
      const table_size = base + array.length;
      table.initial_size = table_size;
      if (table.has_max && table_size > table.max_size) {
        table.max_size = table_size;
      }
      return this.addActiveElementSegment(0, WasmInitExpr.I32Const(base), array);
    }
  
    setTableBounds(min, max = undefined) {
      if (this.tables.length != 0) {
        throw new Error('The table bounds of table \'0\' have already been set.');
      }
      this.addTable(kWasmAnyFunc, min, max);
      return this;
    }
  
    setName(name) {
      this.name = name;
      return this;
    }
  
    toBuffer(debug = false) {
      let binary = new Binary;
      let wasm = this;
  
      // Add header
      binary.emit_header();
  
      // Add type section
      if (wasm.types.length > 0) {
        if (debug) print('emitting types @ ' + binary.length);
        binary.emit_section(kTypeSectionCode, section => {
          section.emit_u32v(wasm.types.length);
          for (let type of wasm.types) {
            if (type instanceof WasmStruct) {
              section.emit_u8(kWasmStructTypeForm);
              section.emit_u32v(type.fields.length);
              for (let field of type.fields) {
                section.emit_type(field.type);
                section.emit_u8(field.mutability ? 1 : 0);
              }
            } else if (type instanceof WasmArray) {
              section.emit_u8(kWasmArrayTypeForm);
              section.emit_type(type.type);
              section.emit_u8(1);  // Only mutable arrays supported currently.
            } else {
              section.emit_u8(kWasmFunctionTypeForm);
              section.emit_u32v(type.params.length);
              for (let param of type.params) {
                section.emit_type(param);
              }
              section.emit_u32v(type.results.length);
              for (let result of type.results) {
                section.emit_type(result);
              }
            }
          }
        });
      }
  
      // Add imports section
      if (wasm.imports.length > 0) {
        if (debug) print('emitting imports @ ' + binary.length);
        binary.emit_section(kImportSectionCode, section => {
          section.emit_u32v(wasm.imports.length);
          for (let imp of wasm.imports) {
            section.emit_string(imp.module);
            section.emit_string(imp.name || '');
            section.emit_u8(imp.kind);
            if (imp.kind == kExternalFunction) {
              section.emit_u32v(imp.type_index);
            } else if (imp.kind == kExternalGlobal) {
              section.emit_type(imp.type);
              section.emit_u8(imp.mutable);
            } else if (imp.kind == kExternalMemory) {
              var has_max = (typeof imp.maximum) != 'undefined';
              var is_shared = (typeof imp.shared) != 'undefined';
              if (is_shared) {
                section.emit_u8(has_max ? 3 : 2);  // flags
              } else {
                section.emit_u8(has_max ? 1 : 0);  // flags
              }
              section.emit_u32v(imp.initial);               // initial
              if (has_max) section.emit_u32v(imp.maximum);  // maximum
            } else if (imp.kind == kExternalTable) {
              section.emit_type(imp.type);
              var has_max = (typeof imp.maximum) != 'undefined';
              section.emit_u8(has_max ? 1 : 0);             // flags
              section.emit_u32v(imp.initial);               // initial
              if (has_max) section.emit_u32v(imp.maximum);  // maximum
            } else if (imp.kind == kExternalException) {
              section.emit_u32v(kExceptionAttribute);
              section.emit_u32v(imp.type_index);
            } else {
              throw new Error('unknown/unsupported import kind ' + imp.kind);
            }
          }
        });
      }
  
      // Add functions declarations
      if (wasm.functions.length > 0) {
        if (debug) print('emitting function decls @ ' + binary.length);
        binary.emit_section(kFunctionSectionCode, section => {
          section.emit_u32v(wasm.functions.length);
          for (let func of wasm.functions) {
            section.emit_u32v(func.type_index);
          }
        });
      }
  
      // Add table section
      if (wasm.tables.length > 0) {
        if (debug) print('emitting tables @ ' + binary.length);
        binary.emit_section(kTableSectionCode, section => {
          section.emit_u32v(wasm.tables.length);
          for (let table of wasm.tables) {
            section.emit_type(table.type);
            section.emit_u8(table.has_max);
            section.emit_u32v(table.initial_size);
            if (table.has_max) section.emit_u32v(table.max_size);
            if (table.has_init) {
              section.emit_init_expr(table.init_expr);
            }
          }
        });
      }
  
      // Add memory section
      if (wasm.memory !== undefined) {
        if (debug) print('emitting memory @ ' + binary.length);
        binary.emit_section(kMemorySectionCode, section => {
          section.emit_u8(1);  // one memory entry
          const has_max = wasm.memory.max !== undefined;
          if (wasm.memory.is_memory64) {
            if (wasm.memory.shared) {
              throw new Error('sharing memory64 is not supported (yet)');
            }
            section.emit_u8(
                has_max ? kLimitsMemory64WithMaximum : kLimitsMemory64NoMaximum);
            section.emit_u64v(wasm.memory.min);
            if (has_max) section.emit_u64v(wasm.memory.max);
          } else {
            section.emit_u8(
                wasm.memory.shared ?
                    (has_max ? kLimitsSharedWithMaximum :
                               kLimitsSharedNoMaximum) :
                    (has_max ? kLimitsWithMaximum : kLimitsNoMaximum));
            section.emit_u32v(wasm.memory.min);
            if (has_max) section.emit_u32v(wasm.memory.max);
          }
        });
      }
  
      // Add event section.
      if (wasm.exceptions.length > 0) {
        if (debug) print('emitting events @ ' + binary.length);
        binary.emit_section(kExceptionSectionCode, section => {
          section.emit_u32v(wasm.exceptions.length);
          for (let type_index of wasm.exceptions) {
            section.emit_u32v(kExceptionAttribute);
            section.emit_u32v(type_index);
          }
        });
      }
  
      // Add global section.
      if (wasm.globals.length > 0) {
        if (debug) print('emitting globals @ ' + binary.length);
        binary.emit_section(kGlobalSectionCode, section => {
          section.emit_u32v(wasm.globals.length);
          for (let global of wasm.globals) {
            section.emit_type(global.type);
            section.emit_u8(global.mutable);
            section.emit_init_expr(global.init);
          }
        });
      }
  
      // Add export table.
      var mem_export = (wasm.memory !== undefined && wasm.memory.exported);
      var exports_count = wasm.exports.length + (mem_export ? 1 : 0);
      if (exports_count > 0) {
        if (debug) print('emitting exports @ ' + binary.length);
        binary.emit_section(kExportSectionCode, section => {
          section.emit_u32v(exports_count);
          for (let exp of wasm.exports) {
            section.emit_string(exp.name);
            section.emit_u8(exp.kind);
            section.emit_u32v(exp.index);
          }
          if (mem_export) {
            section.emit_string('memory');
            section.emit_u8(kExternalMemory);
            section.emit_u8(0);
          }
        });
      }
  
      // Add start function section.
      if (wasm.start_index !== undefined) {
        if (debug) print('emitting start function @ ' + binary.length);
        binary.emit_section(kStartSectionCode, section => {
          section.emit_u32v(wasm.start_index);
        });
      }
  
      // Add element segments
      if (wasm.element_segments.length > 0) {
        if (debug) print('emitting element segments @ ' + binary.length);
        binary.emit_section(kElementSectionCode, section => {
          var segments = wasm.element_segments;
          section.emit_u32v(segments.length);
  
          for (let segment of segments) {
            // Emit flag and header.
            // Each case below corresponds to a flag from
            // https://webassembly.github.io/spec/core/binary/modules.html#element-section
            // (not in increasing order).
            if (segment.is_active()) {
              if (segment.table == 0 && segment.type === undefined) {
                if (segment.expressions_as_elements()) {
                  section.emit_u8(0x04);
                  section.emit_init_expr(segment.offset);
                } else {
                  section.emit_u8(0x00)
                  section.emit_init_expr(segment.offset);
                }
              } else {
                if (segment.expressions_as_elements()) {
                  section.emit_u8(0x06);
                  section.emit_u32v(segment.table);
                  section.emit_init_expr(segment.offset);
                  section.emit_type(segment.type);
                } else {
                  section.emit_u8(0x02);
                  section.emit_u32v(segment.table);
                  section.emit_init_expr(segment.offset);
                  section.emit_u8(kExternalFunction);
                }
              }
            } else {
              if (segment.expressions_as_elements()) {
                if (segment.is_passive()) {
                  section.emit_u8(0x05);
                } else {
                  section.emit_u8(0x07);
                }
                section.emit_type(segment.type);
              } else {
                if (segment.is_passive()) {
                  section.emit_u8(0x01);
                } else {
                  section.emit_u8(0x03);
                }
                section.emit_u8(kExternalFunction);
              }
            }
  
            // Emit elements.
            section.emit_u32v(segment.elements.length);
            for (let element of segment.elements) {
              if (segment.expressions_as_elements()) {
                section.emit_init_expr(element);
              } else {
                section.emit_u32v(element);
              }
            }
          }
        })
      }
  
      // If there are any passive data segments, add the DataCount section.
      if (wasm.data_segments.some(seg => !seg.is_active)) {
        binary.emit_section(kDataCountSectionCode, section => {
          section.emit_u32v(wasm.data_segments.length);
        });
      }
  
      // If there are compilation hints add a custom section 'compilationHints'
      // after the function section and before the code section.
      if (wasm.compilation_hints.length > 0) {
        if (debug) print('emitting compilation hints @ ' + binary.length);
        // Build custom section payload.
        let payloadBinary = new Binary();
        let implicit_compilation_hints_count = wasm.functions.length;
        payloadBinary.emit_u32v(implicit_compilation_hints_count);
  
        // Defaults to the compiler's choice if no better hint was given (0x00).
        let defaultHintByte = kCompilationHintStrategyDefault |
            (kCompilationHintTierDefault << 2) |
            (kCompilationHintTierDefault << 4);
  
        // Emit hint byte for every function defined in this module.
        for (let i = 0; i < implicit_compilation_hints_count; i++) {
          let index = wasm.num_imported_funcs + i;
          var hintByte;
          if (index in wasm.compilation_hints) {
            let hint = wasm.compilation_hints[index];
            hintByte =
                hint.strategy | (hint.baselineTier << 2) | (hint.topTier << 4);
          } else {
            hintByte = defaultHintByte;
          }
          payloadBinary.emit_u8(hintByte);
        }
  
        // Finalize as custom section.
        let name = 'compilationHints';
        let bytes = this.createCustomSection(name, payloadBinary.trunc_buffer());
        binary.emit_bytes(bytes);
      }
  
      // Add function bodies.
      if (wasm.functions.length > 0) {
        // emit function bodies
        if (debug) print('emitting code @ ' + binary.length);
        let section_length = 0;
        binary.emit_section(kCodeSectionCode, section => {
          section.emit_u32v(wasm.functions.length);
          let header = new Binary;
          for (let func of wasm.functions) {
            header.reset();
            // Function body length will be patched later.
            let local_decls = func.locals || [];
            header.emit_u32v(local_decls.length);
            for (let decl of local_decls) {
              header.emit_u32v(decl.count);
              header.emit_type(decl.type);
            }
            section.emit_u32v(header.length + func.body.length);
            section.emit_bytes(header.trunc_buffer());
            // Set to section offset for now, will update.
            func.body_offset = section.length;
            section.emit_bytes(func.body);
          }
          section_length = section.length;
        });
        for (let func of wasm.functions) {
          func.body_offset += binary.length - section_length;
        }
      }
  
      // Add data segments.
      if (wasm.data_segments.length > 0) {
        if (debug) print('emitting data segments @ ' + binary.length);
        binary.emit_section(kDataSectionCode, section => {
          section.emit_u32v(wasm.data_segments.length);
          for (let seg of wasm.data_segments) {
            if (seg.is_active) {
              section.emit_u8(0);  // linear memory index 0 / flags
              if (seg.is_global) {
                // initializer is a global variable
                section.emit_u8(kExprGlobalGet);
                section.emit_u32v(seg.addr);
              } else {
                // initializer is a constant
                section.emit_u8(kExprI32Const);
                section.emit_u32v(seg.addr);
              }
              section.emit_u8(kExprEnd);
            } else {
              section.emit_u8(kPassive);  // flags
            }
            section.emit_u32v(seg.data.length);
            section.emit_bytes(seg.data);
          }
        });
      }
  
      // Add any explicitly added sections
      for (let exp of wasm.explicit) {
        if (debug) print('emitting explicit @ ' + binary.length);
        binary.emit_bytes(exp);
      }
  
      // Add names.
      let num_function_names = 0;
      let num_functions_with_local_names = 0;
      for (let func of wasm.functions) {
        if (func.name !== undefined) ++num_function_names;
        if (func.numLocalNames() > 0) ++num_functions_with_local_names;
      }
      if (num_function_names > 0 || num_functions_with_local_names > 0 ||
          wasm.name !== undefined) {
        if (debug) print('emitting names @ ' + binary.length);
        binary.emit_section(kUnknownSectionCode, section => {
          section.emit_string('name');
          // Emit module name.
          if (wasm.name !== undefined) {
            section.emit_section(kModuleNameCode, name_section => {
              name_section.emit_string(wasm.name);
            });
          }
          // Emit function names.
          if (num_function_names > 0) {
            section.emit_section(kFunctionNamesCode, name_section => {
              name_section.emit_u32v(num_function_names);
              for (let func of wasm.functions) {
                if (func.name === undefined) continue;
                name_section.emit_u32v(func.index);
                name_section.emit_string(func.name);
              }
            });
          }
          // Emit local names.
          if (num_functions_with_local_names > 0) {
            section.emit_section(kLocalNamesCode, name_section => {
              name_section.emit_u32v(num_functions_with_local_names);
              for (let func of wasm.functions) {
                if (func.numLocalNames() == 0) continue;
                name_section.emit_u32v(func.index);
                name_section.emit_u32v(func.numLocalNames());
                let name_index = 0;
                for (let i = 0; i < func.local_names.length; ++i) {
                  if (typeof func.local_names[i] == 'string') {
                    name_section.emit_u32v(name_index);
                    name_section.emit_string(func.local_names[i]);
                    name_index++;
                  } else {
                    name_index += func.local_names[i];
                  }
                }
              }
            });
          }
        });
      }
  
      return binary.trunc_buffer();
    }
  
    toArray(debug = false) {
      return Array.from(this.toBuffer(debug));
    }
  
    instantiate(ffi) {
      let module = this.toModule();
      let instance = new WebAssembly.Instance(module, ffi);
      return instance;
    }
  
    asyncInstantiate(ffi) {
      return WebAssembly.instantiate(this.toBuffer(), ffi)
          .then(({module, instance}) => instance);
    }
  
    toModule(debug = false) {
      return new WebAssembly.Module(this.toBuffer(debug));
    }
  }
  
  function wasmSignedLeb(val, max_len = 5) {
    let res = [];
    for (let i = 0; i < max_len; ++i) {
      let v = val & 0x7f;
      // If {v} sign-extended from 7 to 32 bits is equal to val, we are done.
      if (((v << 25) >> 25) == val) {
        res.push(v);
        return res;
      }
      res.push(v | 0x80);
      val = val >> 7;
    }
    throw new Error(
        'Leb value <' + val + '> exceeds maximum length of ' + max_len);
  }
  
  function wasmI32Const(val) {
    return [kExprI32Const, ...wasmSignedLeb(val, 5)];
  }
  
  // Note: Since {val} is a JS number, the generated constant only has 53 bits of
  // precision.
  function wasmI64Const(val) {
    return [kExprI64Const, ...wasmSignedLeb(val, 10)];
  }
  
  function wasmF32Const(f) {
    // Write in little-endian order at offset 0.
    data_view.setFloat32(0, f, true);
    return [
      kExprF32Const, byte_view[0], byte_view[1], byte_view[2], byte_view[3]
    ];
  }
  
  function wasmF64Const(f) {
    // Write in little-endian order at offset 0.
    data_view.setFloat64(0, f, true);
    return [
      kExprF64Const, byte_view[0], byte_view[1], byte_view[2], byte_view[3],
      byte_view[4], byte_view[5], byte_view[6], byte_view[7]
    ];
  }
  
  function wasmS128Const(f) {
    // Write in little-endian order at offset 0.
    return [kSimdPrefix, kExprS128Const, ...f];
  }
  
  function getOpcodeName(opcode) {
    return globalThis.kWasmOpcodeNames?.[opcode] ?? 'unknown';
  }
  