text: /*
   * Copyright 2016 Ferry Toth, Exalon Delft BV, The Netherlands
   *  This software is provided 'as-is', without any express or implied
   * warranty.  In no event will the author be held liable for any damages
   * arising from the use of this software.
   *  Permission is granted to anyone to use this software for any purpose,
   * including commercial applications, and to alter it and redistribute it
   * freely, subject to the following restrictions:
   *  1. The origin of this software must not be misrepresented; you must not
   *   claim that you wrote the original software. If you use this software
   *   in a product, an acknowledgment in the product documentation would be
   *   appreciated but is not required.
   * 2. Altered source versions must be plainly marked as such, and must not be
   *   misrepresented as being the original software.
   * 3. This notice may not be removed or altered from any source distribution.
   *  Ferry Toth
   * ftoth@exalondelft.nl
   *
   * https://github.com/htot/crc32c
   *
   * Modified by Facebook
   *
   * Original intel whitepaper:
   * "Fast CRC Computation for iSCSI Polynomial Using CRC32 Instruction"
   * https://www.intel.com/content/dam/www/public/us/en/documents/white-papers/crc-iscsi-polynomial-crc32-instruction-paper.pdf
   *
   * 32-bit support dropped
   * use intrinsics instead of inline asm
   * other code cleanup
   */
  
  #include <stdexcept>
  
  #include <folly/hash/detail/ChecksumDetail.h>
  
  #include <folly/CppAttributes.h>
  
  #include <boost/preprocessor/arithmetic/add.hpp>
  #include <boost/preprocessor/arithmetic/sub.hpp>
  #include <boost/preprocessor/repetition/repeat_from_to.hpp>
  
  namespace folly {
  namespace detail {
  
  #if defined(FOLLY_X64) && FOLLY_SSE_PREREQ(4, 2)
  
  namespace crc32_detail {
  
  #define CRCtriplet(crc, buf, offset)                  \
    crc##0 = _mm_crc32_u64(crc##0, *(buf##0 + offset)); \
    crc##1 = _mm_crc32_u64(crc##1, *(buf##1 + offset)); \
    crc##2 = _mm_crc32_u64(crc##2, *(buf##2 + offset)); \
    FOLLY_FALLTHROUGH;
  
  #define CRCduplet(crc, buf, offset)                   \
    crc##0 = _mm_crc32_u64(crc##0, *(buf##0 + offset)); \
    crc##1 = _mm_crc32_u64(crc##1, *(buf##1 + offset));
  
  #define CRCsinglet(crc, buf, offset)                    \
    crc = _mm_crc32_u64(crc, *(uint64_t*)(buf + offset)); \
    FOLLY_FALLTHROUGH;
  
  #define CASEREPEAT_TRIPLET(unused, count, total)    \
    case BOOST_PP_ADD(1, BOOST_PP_SUB(total, count)): \
      CRCtriplet(crc, next, -BOOST_PP_ADD(1, BOOST_PP_SUB(total, count)));
  
  #define CASEREPEAT_SINGLET(unused, count, total) \
    case BOOST_PP_SUB(total, count):               \
      CRCsinglet(crc0, next, -BOOST_PP_SUB(total, count) * 8);
  
  // Numbers taken directly from intel whitepaper.
  // clang-format off
  const uint64_t clmul_constants[] = {
      0x14cd00bd6, 0x105ec76f0, 0x0ba4fc28e, 0x14cd00bd6,
      0x1d82c63da, 0x0f20c0dfe, 0x09e4addf8, 0x0ba4fc28e,
      0x039d3b296, 0x1384aa63a, 0x102f9b8a2, 0x1d82c63da,
      0x14237f5e6, 0x01c291d04, 0x00d3b6092, 0x09e4addf8,
      0x0c96cfdc0, 0x0740eef02, 0x18266e456, 0x039d3b296,
      0x0daece73e, 0x0083a6eec, 0x0ab7aff2a, 0x102f9b8a2,
      0x1248ea574, 0x1c1733996, 0x083348832, 0x14237f5e6,
      0x12c743124, 0x02ad91c30, 0x0b9e02b86, 0x00d3b6092,
      0x018b33a4e, 0x06992cea2, 0x1b331e26a, 0x0c96cfdc0,
      0x17d35ba46, 0x07e908048, 0x1bf2e8b8a, 0x18266e456,
      0x1a3e0968a, 0x11ed1f9d8, 0x0ce7f39f4, 0x0daece73e,
      0x061d82e56, 0x0f1d0f55e, 0x0d270f1a2, 0x0ab7aff2a,
      0x1c3f5f66c, 0x0a87ab8a8, 0x12ed0daac, 0x1248ea574,
      0x065863b64, 0x08462d800, 0x11eef4f8e, 0x083348832,
      0x1ee54f54c, 0x071d111a8, 0x0b3e32c28, 0x12c743124,
      0x0064f7f26, 0x0ffd852c6, 0x0dd7e3b0c, 0x0b9e02b86,
      0x0f285651c, 0x0dcb17aa4, 0x010746f3c, 0x018b33a4e,
      0x1c24afea4, 0x0f37c5aee, 0x0271d9844, 0x1b331e26a,
      0x08e766a0c, 0x06051d5a2, 0x093a5f730, 0x17d35ba46,
      0x06cb08e5c, 0x11d5ca20e, 0x06b749fb2, 0x1bf2e8b8a,
      0x1167f94f2, 0x021f3d99c, 0x0cec3662e, 0x1a3e0968a,
      0x19329634a, 0x08f158014, 0x0e6fc4e6a, 0x0ce7f39f4,
      0x08227bb8a, 0x1a5e82106, 0x0b0cd4768, 0x061d82e56,
      0x13c2b89c4, 0x188815ab2, 0x0d7a4825c, 0x0d270f1a2,
      0x10f5ff2ba, 0x105405f3e, 0x00167d312, 0x1c3f5f66c,
      0x0f6076544, 0x0e9adf796, 0x026f6a60a, 0x12ed0daac,
      0x1a2adb74e, 0x096638b34, 0x19d34af3a, 0x065863b64,
      0x049c3cc9c, 0x1e50585a0, 0x068bce87a, 0x11eef4f8e,
      0x1524fa6c6, 0x19f1c69dc, 0x16cba8aca, 0x1ee54f54c,
      0x042d98888, 0x12913343e, 0x1329d9f7e, 0x0b3e32c28,
      0x1b1c69528, 0x088f25a3a, 0x02178513a, 0x0064f7f26,
      0x0e0ac139e, 0x04e36f0b0, 0x0170076fa, 0x0dd7e3b0c,
      0x141a1a2e2, 0x0bd6f81f8, 0x16ad828b4, 0x0f285651c,
      0x041d17b64, 0x19425cbba, 0x1fae1cc66, 0x010746f3c,
      0x1a75b4b00, 0x18db37e8a, 0x0f872e54c, 0x1c24afea4,
      0x01e41e9fc, 0x04c144932, 0x086d8e4d2, 0x0271d9844,
      0x160f7af7a, 0x052148f02, 0x05bb8f1bc, 0x08e766a0c,
      0x0a90fd27a, 0x0a3c6f37a, 0x0b3af077a, 0x093a5f730,
      0x04984d782, 0x1d22c238e, 0x0ca6ef3ac, 0x06cb08e5c,
      0x0234e0b26, 0x063ded06a, 0x1d88abd4a, 0x06b749fb2,
      0x04597456a, 0x04d56973c, 0x0e9e28eb4, 0x1167f94f2,
      0x07b3ff57a, 0x19385bf2e, 0x0c9c8b782, 0x0cec3662e,
      0x13a9cba9e, 0x0e417f38a, 0x093e106a4, 0x19329634a,
      0x167001a9c, 0x14e727980, 0x1ddffc5d4, 0x0e6fc4e6a,
      0x00df04680, 0x0d104b8fc, 0x02342001e, 0x08227bb8a,
      0x00a2a8d7e, 0x05b397730, 0x168763fa6, 0x0b0cd4768,
      0x1ed5a407a, 0x0e78eb416, 0x0d2c3ed1a, 0x13c2b89c4,
      0x0995a5724, 0x1641378f0, 0x19b1afbc4, 0x0d7a4825c,
      0x109ffedc0, 0x08d96551c, 0x0f2271e60, 0x10f5ff2ba,
      0x00b0bf8ca, 0x00bf80dd2, 0x123888b7a, 0x00167d312,
      0x1e888f7dc, 0x18dcddd1c, 0x002ee03b2, 0x0f6076544,
      0x183e8d8fe, 0x06a45d2b2, 0x133d7a042, 0x026f6a60a,
      0x116b0f50c, 0x1dd3e10e8, 0x05fabe670, 0x1a2adb74e,
      0x130004488, 0x0de87806c, 0x000bcf5f6, 0x19d34af3a,
      0x18f0c7078, 0x014338754, 0x017f27698, 0x049c3cc9c,
      0x058ca5f00, 0x15e3e77ee, 0x1af900c24, 0x068bce87a,
      0x0b5cfca28, 0x0dd07448e, 0x0ded288f8, 0x1524fa6c6,
      0x059f229bc, 0x1d8048348, 0x06d390dec, 0x16cba8aca,
      0x037170390, 0x0a3e3e02c, 0x06353c1cc, 0x042d98888,
      0x0c4584f5c, 0x0d73c7bea, 0x1f16a3418, 0x1329d9f7e,
      0x0531377e2, 0x185137662, 0x1d8d9ca7c, 0x1b1c69528,
      0x0b25b29f2, 0x18a08b5bc, 0x19fb2a8b0, 0x02178513a,
      0x1a08fe6ac, 0x1da758ae0, 0x045cddf4e, 0x0e0ac139e,
      0x1a91647f2, 0x169cf9eb0, 0x1a0f717c4, 0x0170076fa,
  };
  // clang-format on
  
  /*
   * CombineCRC performs pclmulqdq multiplication of 2 partial CRC's and a well
   * chosen constant and xor's these with the remaining CRC.
   */
  uint64_t CombineCRC(
      size_t block_size,
      uint64_t crc0,
      uint64_t crc1,
      uint64_t crc2,
      const uint64_t* next2) {
    const auto multiplier =
        *(reinterpret_cast<const __m128i*>(clmul_constants) + block_size - 1);
    const auto crc0_xmm = _mm_set_epi64x(0, crc0);
    const auto res0 = _mm_clmulepi64_si128(crc0_xmm, multiplier, 0x00);
    const auto crc1_xmm = _mm_set_epi64x(0, crc1);
    const auto res1 = _mm_clmulepi64_si128(crc1_xmm, multiplier, 0x10);
    const auto res = _mm_xor_si128(res0, res1);
    crc0 = _mm_cvtsi128_si64(res);
    crc0 = crc0 ^ *((uint64_t*)next2 - 1);
    crc2 = _mm_crc32_u64(crc2, crc0);
    return crc2;
  }
  
  // Generates a block that will crc up to 7 bytes of unaligned data.
  // Always inline to avoid overhead on small crc sizes.
  FOLLY_ALWAYS_INLINE void align_to_8(
      size_t align,
      uint64_t& crc0, // crc so far, updated on return
      const unsigned char*& next) { // next data pointer, updated on return
    uint32_t crc32bit = static_cast<uint32_t>(crc0);
    if (align & 0x04) {
      crc32bit = _mm_crc32_u32(crc32bit, *(uint32_t*)next);
      next += sizeof(uint32_t);
    }
    if (align & 0x02) {
      crc32bit = _mm_crc32_u16(crc32bit, *(uint16_t*)next);
      next += sizeof(uint16_t);
    }
    if (align & 0x01) {
      crc32bit = _mm_crc32_u8(crc32bit, *(next));
      next++;
    }
    crc0 = crc32bit;
  }
  
  // The main loop for large crc sizes. Generates three crc32c
  // streams, of varying block sizes, using a duff's device.
  void triplet_loop(
      size_t block_size,
      uint64_t& crc0, // crc so far, updated on return
      const unsigned char*& next, // next data pointer, updated on return
      size_t n) { // block count
    uint64_t crc1 = 0, crc2 = 0;
    // points to the first byte of the next block
    const uint64_t* next0 = (uint64_t*)next + block_size;
    const uint64_t* next1 = next0 + block_size;
    const uint64_t* next2 = next1 + block_size;
  
    // Use Duff's device, a for() loop inside a switch()
    // statement. This needs to execute at least once, round len
    // down to nearest triplet multiple
    switch (block_size) {
      case 128:
        do {
          // jumps here for a full block of len 128
          CRCtriplet(crc, next, -128);
  
          // Generates case statements from 127 to 2 of form:
          // case 127:
          //    CRCtriplet(crc, next, -127);
          //
          // MSVC has a max preprocessor expansion depth of 255, which is
          // exceeded if this is a single statement.
          BOOST_PP_REPEAT_FROM_TO(0, 64, CASEREPEAT_TRIPLET, 126);
          BOOST_PP_REPEAT_FROM_TO(0, 62, CASEREPEAT_TRIPLET, 62);
  
          // For the last byte, the three crc32c streams must be combined
          // using carry-less multiplication.
          case 1:
            CRCduplet(crc, next, -1); // the final triplet is actually only 2
            crc0 = CombineCRC(block_size, crc0, crc1, crc2, next2);
            if (--n > 0) {
              crc1 = crc2 = 0;
              block_size = 128;
              // points to the first byte of the next block
              next0 = next2 + 128;
              next1 = next0 + 128; // from here on all blocks are 128 long
              next2 = next1 + 128;
            }
            FOLLY_FALLTHROUGH;
          case 0:;
        } while (n > 0);
    }
  
    next = (const unsigned char*)next2;
  }
  
  } // namespace crc32c_detail
  
  /* Compute CRC-32C using the Intel hardware instruction. */
  FOLLY_TARGET_ATTRIBUTE("sse4.2")
  uint32_t crc32c_hw(const uint8_t* buf, size_t len, uint32_t crc) {
    const unsigned char* next = (const unsigned char*)buf;
    size_t count;
    uint64_t crc0;
    crc0 = crc;
  
    if (len >= 8) {
      // if len > 216 then align and use triplets
      if (len > 216) {
        size_t align = (8 - (uintptr_t)next) & 7;
        crc32_detail::align_to_8(align, crc0, next);
        len -= align;
  
        count = len / 24; // number of triplets
        len %= 24; // bytes remaining
        size_t n = count >> 7; // #blocks = first block + full blocks
        size_t block_size = count & 127;
        if (block_size == 0) {
          block_size = 128;
        } else {
          n++;
        }
  
        // This is a separate function call mainly to stop
        // clang from spilling registers.
        crc32_detail::triplet_loop(block_size, crc0, next, n);
      }
  
      size_t count2 = len >> 3;
      len = len & 7;
      next += (count2 * 8);
  
      // Generates a duff device for the last 128 bytes of aligned data.
      switch (count2) {
        // Generates case statements of the form:
        // case 27:
        //   CRCsinglet(crc0, next, -27 * 8);
        BOOST_PP_REPEAT_FROM_TO(0, 27, CASEREPEAT_SINGLET, 27);
        case 0:;
      }
    }
  
    // compute the crc for up to seven trailing bytes
    crc32_detail::align_to_8(len, crc0, next);
    return (uint32_t)crc0;
  }
  
  #else
  
  uint32_t
  crc32c_hw(const uint8_t* /* buf */, size_t /* len */, uint32_t /* crc */) {
    throw std::runtime_error("crc32_hw is not implemented on this platform");
  }
  
  #endif
  
  } // namespace detail
  } // namespace folly
  