text: /*
   * SHA-256 algorithm as described at
   *
   *   http://csrc.nist.gov/cryptval/shs.html
   */
  
  #include "ssh.h"
  #include <assert.h>
  
  /*
   * Start by deciding whether we can support hardware SHA at all.
   */
  #define HW_SHA256_NONE 0
  #define HW_SHA256_NI 1
  #define HW_SHA256_NEON 2
  
  #ifdef _FORCE_SHA_NI
  #   define HW_SHA256 HW_SHA256_NI
  #elif defined(__clang__)
  #   if __has_attribute(target) && __has_include(<wmmintrin.h>) &&       \
      (defined(__x86_64__) || defined(__i386))
  #       define HW_SHA256 HW_SHA256_NI
  #   endif
  #elif defined(__GNUC__)
  #    if (__GNUC__ > 4 || (__GNUC__ == 4 && __GNUC_MINOR__ >= 9)) && \
          (defined(__x86_64__) || defined(__i386))
  #       define HW_SHA256 HW_SHA256_NI
  #    endif
  #elif defined (_MSC_VER)
  #   if (defined(_M_X64) || defined(_M_IX86)) && _MSC_FULL_VER >= 150030729
  #      define HW_SHA256 HW_SHA256_NI
  #   endif
  #endif
  
  #ifdef _FORCE_SHA_NEON
  #   define HW_SHA256 HW_SHA256_NEON
  #elif defined __BYTE_ORDER__ && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
      /* Arm can potentially support both endiannesses, but this code
       * hasn't been tested on anything but little. If anyone wants to
       * run big-endian, they'll need to fix it first. */
  #elif defined __ARM_FEATURE_CRYPTO
      /* If the Arm crypto extension is available already, we can
       * support NEON SHA without having to enable anything by hand */
  #   define HW_SHA256 HW_SHA256_NEON
  #elif defined(__clang__)
  #   if __has_attribute(target) && __has_include(<arm_neon.h>) &&       \
      (defined(__aarch64__))
          /* clang can enable the crypto extension in AArch64 using
           * __attribute__((target)) */
  #       define HW_SHA256 HW_SHA256_NEON
  #       define USE_CLANG_ATTR_TARGET_AARCH64
  #   endif
  #elif defined _MSC_VER
      /* Visual Studio supports the crypto extension when targeting
       * AArch64, but as of VS2017, the AArch32 header doesn't quite
       * manage it (declaring the shae/shad intrinsics without a round
       * key operand). */
  #   if defined _M_ARM64
  #       define HW_SHA256 HW_SHA256_NEON
  #       if defined _M_ARM64
  #           define USE_ARM64_NEON_H /* unusual header name in this case */
  #       endif
  #   endif
  #endif
  
  #if defined _FORCE_SOFTWARE_SHA || !defined HW_SHA256
  #   undef HW_SHA256
  #   define HW_SHA256 HW_SHA256_NONE
  #endif
  
  /*
   * The actual query function that asks if hardware acceleration is
   * available.
   */
  static bool sha256_hw_available(void);
  
  /*
   * The top-level selection function, caching the results of
   * sha256_hw_available() so it only has to run once.
   */
  static bool sha256_hw_available_cached(void)
  {
      static bool initialised = false;
      static bool hw_available;
      if (!initialised) {
          hw_available = sha256_hw_available();
          initialised = true;
      }
      return hw_available;
  }
  
  static ssh_hash *sha256_select(const ssh_hashalg *alg)
  {
      const ssh_hashalg *real_alg =
          sha256_hw_available_cached() ? &ssh_sha256_hw : &ssh_sha256_sw;
  
      return ssh_hash_new(real_alg);
  }
  
  const ssh_hashalg ssh_sha256 = {
      .new = sha256_select,
      .hlen = 32,
      .blocklen = 64,
      HASHALG_NAMES_ANNOTATED("SHA-256", "dummy selector vtable"),
  };
  
  /* ----------------------------------------------------------------------
   * Definitions likely to be helpful to multiple implementations.
   */
  
  static const uint32_t sha256_initial_state[] = {
      0x6a09e667, 0xbb67ae85, 0x3c6ef372, 0xa54ff53a,
      0x510e527f, 0x9b05688c, 0x1f83d9ab, 0x5be0cd19,
  };
  
  static const uint32_t sha256_round_constants[] = {
      0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5,
      0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
      0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3,
      0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
      0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc,
      0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
      0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7,
      0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
      0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13,
      0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
      0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3,
      0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
      0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5,
      0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
      0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208,
      0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2,
  };
  
  #define SHA256_ROUNDS 64
  
  typedef struct sha256_block sha256_block;
  struct sha256_block {
      uint8_t block[64];
      size_t used;
      uint64_t len;
  };
  
  static inline void sha256_block_setup(sha256_block *blk)
  {
      blk->used = 0;
      blk->len = 0;
  }
  
  static inline bool sha256_block_write(
      sha256_block *blk, const void **vdata, size_t *len)
  {
      size_t blkleft = sizeof(blk->block) - blk->used;
      size_t chunk = *len < blkleft ? *len : blkleft;
  
      const uint8_t *p = *vdata;
      memcpy(blk->block + blk->used, p, chunk);
      *vdata = p + chunk;
      *len -= chunk;
      blk->used += chunk;
      blk->len += chunk;
  
      if (blk->used == sizeof(blk->block)) {
          blk->used = 0;
          return true;
      }
  
      return false;
  }
  
  static inline void sha256_block_pad(sha256_block *blk, BinarySink *bs)
  {
      uint64_t final_len = blk->len << 3;
      size_t pad = 1 + (63 & (55 - blk->used));
  
      put_byte(bs, 0x80);
      for (size_t i = 1; i < pad; i++)
          put_byte(bs, 0);
      put_uint64(bs, final_len);
  
      assert(blk->used == 0 && "Should have exactly hit a block boundary");
  }
  
  /* ----------------------------------------------------------------------
   * Software implementation of SHA-256.
   */
  
  static inline uint32_t ror(uint32_t x, unsigned y)
  {
      return (x << (31 & -y)) | (x >> (31 & y));
  }
  
  static inline uint32_t Ch(uint32_t ctrl, uint32_t if1, uint32_t if0)
  {
      return if0 ^ (ctrl & (if1 ^ if0));
  }
  
  static inline uint32_t Maj(uint32_t x, uint32_t y, uint32_t z)
  {
      return (x & y) | (z & (x | y));
  }
  
  static inline uint32_t Sigma_0(uint32_t x)
  {
      return ror(x,2) ^ ror(x,13) ^ ror(x,22);
  }
  
  static inline uint32_t Sigma_1(uint32_t x)
  {
      return ror(x,6) ^ ror(x,11) ^ ror(x,25);
  }
  
  static inline uint32_t sigma_0(uint32_t x)
  {
      return ror(x,7) ^ ror(x,18) ^ (x >> 3);
  }
  
  static inline uint32_t sigma_1(uint32_t x)
  {
      return ror(x,17) ^ ror(x,19) ^ (x >> 10);
  }
  
  static inline void sha256_sw_round(
      unsigned round_index, const uint32_t *schedule,
      uint32_t *a, uint32_t *b, uint32_t *c, uint32_t *d,
      uint32_t *e, uint32_t *f, uint32_t *g, uint32_t *h)
  {
      uint32_t t1 = *h + Sigma_1(*e) + Ch(*e,*f,*g) +
          sha256_round_constants[round_index] + schedule[round_index];
  
      uint32_t t2 = Sigma_0(*a) + Maj(*a,*b,*c);
  
      *d += t1;
      *h = t1 + t2;
  }
  
  static void sha256_sw_block(uint32_t *core, const uint8_t *block)
  {
      uint32_t w[SHA256_ROUNDS];
      uint32_t a,b,c,d,e,f,g,h;
  
      for (size_t t = 0; t < 16; t++)
          w[t] = GET_32BIT_MSB_FIRST(block + 4*t);
  
      for (size_t t = 16; t < SHA256_ROUNDS; t++)
          w[t] = sigma_1(w[t-2]) + w[t-7] + sigma_0(w[t-15]) + w[t-16];
  
      a = core[0]; b = core[1]; c = core[2]; d = core[3];
      e = core[4]; f = core[5]; g = core[6]; h = core[7];
  
      for (size_t t = 0; t < SHA256_ROUNDS; t += 8) {
          sha256_sw_round(t+0, w, &a,&b,&c,&d,&e,&f,&g,&h);
          sha256_sw_round(t+1, w, &h,&a,&b,&c,&d,&e,&f,&g);
          sha256_sw_round(t+2, w, &g,&h,&a,&b,&c,&d,&e,&f);
          sha256_sw_round(t+3, w, &f,&g,&h,&a,&b,&c,&d,&e);
          sha256_sw_round(t+4, w, &e,&f,&g,&h,&a,&b,&c,&d);
          sha256_sw_round(t+5, w, &d,&e,&f,&g,&h,&a,&b,&c);
          sha256_sw_round(t+6, w, &c,&d,&e,&f,&g,&h,&a,&b);
          sha256_sw_round(t+7, w, &b,&c,&d,&e,&f,&g,&h,&a);
      }
  
      core[0] += a; core[1] += b; core[2] += c; core[3] += d;
      core[4] += e; core[5] += f; core[6] += g; core[7] += h;
  
      smemclr(w, sizeof(w));
  }
  
  typedef struct sha256_sw {
      uint32_t core[8];
      sha256_block blk;
      BinarySink_IMPLEMENTATION;
      ssh_hash hash;
  } sha256_sw;
  
  static void sha256_sw_write(BinarySink *bs, const void *vp, size_t len);
  
  static ssh_hash *sha256_sw_new(const ssh_hashalg *alg)
  {
      sha256_sw *s = snew(sha256_sw);
  
      s->hash.vt = alg;
      BinarySink_INIT(s, sha256_sw_write);
      BinarySink_DELEGATE_INIT(&s->hash, s);
      return &s->hash;
  }
  
  static void sha256_sw_reset(ssh_hash *hash)
  {
      sha256_sw *s = container_of(hash, sha256_sw, hash);
  
      memcpy(s->core, sha256_initial_state, sizeof(s->core));
      sha256_block_setup(&s->blk);
  }
  
  static void sha256_sw_copyfrom(ssh_hash *hcopy, ssh_hash *horig)
  {
      sha256_sw *copy = container_of(hcopy, sha256_sw, hash);
      sha256_sw *orig = container_of(horig, sha256_sw, hash);
  
      memcpy(copy, orig, sizeof(*copy));
      BinarySink_COPIED(copy);
      BinarySink_DELEGATE_INIT(&copy->hash, copy);
  }
  
  static void sha256_sw_free(ssh_hash *hash)
  {
      sha256_sw *s = container_of(hash, sha256_sw, hash);
  
      smemclr(s, sizeof(*s));
      sfree(s);
  }
  
  static void sha256_sw_write(BinarySink *bs, const void *vp, size_t len)
  {
      sha256_sw *s = BinarySink_DOWNCAST(bs, sha256_sw);
  
      while (len > 0)
          if (sha256_block_write(&s->blk, &vp, &len))
              sha256_sw_block(s->core, s->blk.block);
  }
  
  static void sha256_sw_digest(ssh_hash *hash, uint8_t *digest)
  {
      sha256_sw *s = container_of(hash, sha256_sw, hash);
  
      sha256_block_pad(&s->blk, BinarySink_UPCAST(s));
      for (size_t i = 0; i < 8; i++)
          PUT_32BIT_MSB_FIRST(digest + 4*i, s->core[i]);
  }
  
  const ssh_hashalg ssh_sha256_sw = {
      .new = sha256_sw_new,
      .reset = sha256_sw_reset,
      .copyfrom = sha256_sw_copyfrom,
      .digest = sha256_sw_digest,
      .free = sha256_sw_free,
      .hlen = 32,
      .blocklen = 64,
      HASHALG_NAMES_ANNOTATED("SHA-256", "unaccelerated"),
  };
  
  /* ----------------------------------------------------------------------
   * Hardware-accelerated implementation of SHA-256 using x86 SHA-NI.
   */
  
  #if HW_SHA256 == HW_SHA256_NI
  
  /*
   * Set target architecture for Clang and GCC
   */
  #if defined(__clang__) || defined(__GNUC__)
  #    define FUNC_ISA __attribute__ ((target("sse4.1,sha")))
  #if !defined(__clang__)
  #    pragma GCC target("sha")
  #    pragma GCC target("sse4.1")
  #endif
  #else
  #    define FUNC_ISA
  #endif
  
  #include <wmmintrin.h>
  #include <smmintrin.h>
  #include <immintrin.h>
  #if defined(__clang__) || defined(__GNUC__)
  #include <shaintrin.h>
  #endif
  
  #if defined(__clang__) || defined(__GNUC__)
  #include <cpuid.h>
  #define GET_CPU_ID_0(out)                               \
      __cpuid(0, (out)[0], (out)[1], (out)[2], (out)[3])
  #define GET_CPU_ID_7(out)                                       \
      __cpuid_count(7, 0, (out)[0], (out)[1], (out)[2], (out)[3])
  #else
  #define GET_CPU_ID_0(out) __cpuid(out, 0)
  #define GET_CPU_ID_7(out) __cpuidex(out, 7, 0)
  #endif
  
  static bool sha256_hw_available(void)
  {
      unsigned int CPUInfo[4];
      GET_CPU_ID_0(CPUInfo);
      if (CPUInfo[0] < 7)
          return false;
  
      GET_CPU_ID_7(CPUInfo);
      return CPUInfo[1] & (1 << 29); /* Check SHA */
  }
  
  /* SHA256 implementation using new instructions
     The code is based on Jeffrey Walton's SHA256 implementation:
     https://github.com/noloader/SHA-Intrinsics
  */
  FUNC_ISA
  static inline void sha256_ni_block(__m128i *core, const uint8_t *p)
  {
      __m128i STATE0, STATE1;
      __m128i MSG, TMP;
      __m128i MSG0, MSG1, MSG2, MSG3;
      const __m128i *block = (const __m128i *)p;
      const __m128i MASK = _mm_set_epi64x(
          0x0c0d0e0f08090a0bULL, 0x0405060700010203ULL);
  
      /* Load initial values */
      STATE0 = core[0];
      STATE1 = core[1];
  
      /* Rounds 0-3 */
      MSG = _mm_loadu_si128(block);
      MSG0 = _mm_shuffle_epi8(MSG, MASK);
      MSG = _mm_add_epi32(MSG0, _mm_set_epi64x(
                              0xE9B5DBA5B5C0FBCFULL, 0x71374491428A2F98ULL));
      STATE1 = _mm_sha256rnds2_epu32(STATE1, STATE0, MSG);
      MSG = _mm_shuffle_epi32(MSG, 0x0E);
      STATE0 = _mm_sha256rnds2_epu32(STATE0, STATE1, MSG);
  
      /* Rounds 4-7 */
      MSG1 = _mm_loadu_si128(block + 1);
      MSG1 = _mm_shuffle_epi8(MSG1, MASK);
      MSG = _mm_add_epi32(MSG1, _mm_set_epi64x(
                              0xAB1C5ED5923F82A4ULL, 0x59F111F13956C25BULL));
      STATE1 = _mm_sha256rnds2_epu32(STATE1, STATE0, MSG);
      MSG = _mm_shuffle_epi32(MSG, 0x0E);
      STATE0 = _mm_sha256rnds2_epu32(STATE0, STATE1, MSG);
      MSG0 = _mm_sha256msg1_epu32(MSG0, MSG1);
  
      /* Rounds 8-11 */
      MSG2 = _mm_loadu_si128(block + 2);
      MSG2 = _mm_shuffle_epi8(MSG2, MASK);
      MSG = _mm_add_epi32(MSG2, _mm_set_epi64x(
                              0x550C7DC3243185BEULL, 0x12835B01D807AA98ULL));
      STATE1 = _mm_sha256rnds2_epu32(STATE1, STATE0, MSG);
      MSG = _mm_shuffle_epi32(MSG, 0x0E);
      STATE0 = _mm_sha256rnds2_epu32(STATE0, STATE1, MSG);
      MSG1 = _mm_sha256msg1_epu32(MSG1, MSG2);
  
      /* Rounds 12-15 */
      MSG3 = _mm_loadu_si128(block + 3);
      MSG3 = _mm_shuffle_epi8(MSG3, MASK);
      MSG = _mm_add_epi32(MSG3, _mm_set_epi64x(
                              0xC19BF1749BDC06A7ULL, 0x80DEB1FE72BE5D74ULL));
      STATE1 = _mm_sha256rnds2_epu32(STATE1, STATE0, MSG);
      TMP = _mm_alignr_epi8(MSG3, MSG2, 4);
      MSG0 = _mm_add_epi32(MSG0, TMP);
      MSG0 = _mm_sha256msg2_epu32(MSG0, MSG3);
      MSG = _mm_shuffle_epi32(MSG, 0x0E);
      STATE0 = _mm_sha256rnds2_epu32(STATE0, STATE1, MSG);
      MSG2 = _mm_sha256msg1_epu32(MSG2, MSG3);
  
      /* Rounds 16-19 */
      MSG = _mm_add_epi32(MSG0, _mm_set_epi64x(
                              0x240CA1CC0FC19DC6ULL, 0xEFBE4786E49B69C1ULL));
      STATE1 = _mm_sha256rnds2_epu32(STATE1, STATE0, MSG);
      TMP = _mm_alignr_epi8(MSG0, MSG3, 4);
      MSG1 = _mm_add_epi32(MSG1, TMP);
      MSG1 = _mm_sha256msg2_epu32(MSG1, MSG0);
      MSG = _mm_shuffle_epi32(MSG, 0x0E);
      STATE0 = _mm_sha256rnds2_epu32(STATE0, STATE1, MSG);
      MSG3 = _mm_sha256msg1_epu32(MSG3, MSG0);
  
      /* Rounds 20-23 */
      MSG = _mm_add_epi32(MSG1, _mm_set_epi64x(
                              0x76F988DA5CB0A9DCULL, 0x4A7484AA2DE92C6FULL));
      STATE1 = _mm_sha256rnds2_epu32(STATE1, STATE0, MSG);
      TMP = _mm_alignr_epi8(MSG1, MSG0, 4);
      MSG2 = _mm_add_epi32(MSG2, TMP);
      MSG2 = _mm_sha256msg2_epu32(MSG2, MSG1);
      MSG = _mm_shuffle_epi32(MSG, 0x0E);
      STATE0 = _mm_sha256rnds2_epu32(STATE0, STATE1, MSG);
      MSG0 = _mm_sha256msg1_epu32(MSG0, MSG1);
  
      /* Rounds 24-27 */
      MSG = _mm_add_epi32(MSG2, _mm_set_epi64x(
                              0xBF597FC7B00327C8ULL, 0xA831C66D983E5152ULL));
      STATE1 = _mm_sha256rnds2_epu32(STATE1, STATE0, MSG);
      TMP = _mm_alignr_epi8(MSG2, MSG1, 4);
      MSG3 = _mm_add_epi32(MSG3, TMP);
      MSG3 = _mm_sha256msg2_epu32(MSG3, MSG2);
      MSG = _mm_shuffle_epi32(MSG, 0x0E);
      STATE0 = _mm_sha256rnds2_epu32(STATE0, STATE1, MSG);
      MSG1 = _mm_sha256msg1_epu32(MSG1, MSG2);
  
      /* Rounds 28-31 */
      MSG = _mm_add_epi32(MSG3, _mm_set_epi64x(
                              0x1429296706CA6351ULL,  0xD5A79147C6E00BF3ULL));
      STATE1 = _mm_sha256rnds2_epu32(STATE1, STATE0, MSG);
      TMP = _mm_alignr_epi8(MSG3, MSG2, 4);
      MSG0 = _mm_add_epi32(MSG0, TMP);
      MSG0 = _mm_sha256msg2_epu32(MSG0, MSG3);
      MSG = _mm_shuffle_epi32(MSG, 0x0E);
      STATE0 = _mm_sha256rnds2_epu32(STATE0, STATE1, MSG);
      MSG2 = _mm_sha256msg1_epu32(MSG2, MSG3);
  
      /* Rounds 32-35 */
      MSG = _mm_add_epi32(MSG0, _mm_set_epi64x(
                              0x53380D134D2C6DFCULL, 0x2E1B213827B70A85ULL));
      STATE1 = _mm_sha256rnds2_epu32(STATE1, STATE0, MSG);
      TMP = _mm_alignr_epi8(MSG0, MSG3, 4);
      MSG1 = _mm_add_epi32(MSG1, TMP);
      MSG1 = _mm_sha256msg2_epu32(MSG1, MSG0);
      MSG = _mm_shuffle_epi32(MSG, 0x0E);
      STATE0 = _mm_sha256rnds2_epu32(STATE0, STATE1, MSG);
      MSG3 = _mm_sha256msg1_epu32(MSG3, MSG0);
  
      /* Rounds 36-39 */
      MSG = _mm_add_epi32(MSG1, _mm_set_epi64x(
                              0x92722C8581C2C92EULL, 0x766A0ABB650A7354ULL));
      STATE1 = _mm_sha256rnds2_epu32(STATE1, STATE0, MSG);
      TMP = _mm_alignr_epi8(MSG1, MSG0, 4);
      MSG2 = _mm_add_epi32(MSG2, TMP);
      MSG2 = _mm_sha256msg2_epu32(MSG2, MSG1);
      MSG = _mm_shuffle_epi32(MSG, 0x0E);
      STATE0 = _mm_sha256rnds2_epu32(STATE0, STATE1, MSG);
      MSG0 = _mm_sha256msg1_epu32(MSG0, MSG1);
  
      /* Rounds 40-43 */
      MSG = _mm_add_epi32(MSG2, _mm_set_epi64x(
                              0xC76C51A3C24B8B70ULL, 0xA81A664BA2BFE8A1ULL));
      STATE1 = _mm_sha256rnds2_epu32(STATE1, STATE0, MSG);
      TMP = _mm_alignr_epi8(MSG2, MSG1, 4);
      MSG3 = _mm_add_epi32(MSG3, TMP);
      MSG3 = _mm_sha256msg2_epu32(MSG3, MSG2);
      MSG = _mm_shuffle_epi32(MSG, 0x0E);
      STATE0 = _mm_sha256rnds2_epu32(STATE0, STATE1, MSG);
      MSG1 = _mm_sha256msg1_epu32(MSG1, MSG2);
  
      /* Rounds 44-47 */
      MSG = _mm_add_epi32(MSG3, _mm_set_epi64x(
                              0x106AA070F40E3585ULL, 0xD6990624D192E819ULL));
      STATE1 = _mm_sha256rnds2_epu32(STATE1, STATE0, MSG);
      TMP = _mm_alignr_epi8(MSG3, MSG2, 4);
      MSG0 = _mm_add_epi32(MSG0, TMP);
      MSG0 = _mm_sha256msg2_epu32(MSG0, MSG3);
      MSG = _mm_shuffle_epi32(MSG, 0x0E);
      STATE0 = _mm_sha256rnds2_epu32(STATE0, STATE1, MSG);
      MSG2 = _mm_sha256msg1_epu32(MSG2, MSG3);
  
      /* Rounds 48-51 */
      MSG = _mm_add_epi32(MSG0, _mm_set_epi64x(
                              0x34B0BCB52748774CULL, 0x1E376C0819A4C116ULL));
      STATE1 = _mm_sha256rnds2_epu32(STATE1, STATE0, MSG);
      TMP = _mm_alignr_epi8(MSG0, MSG3, 4);
      MSG1 = _mm_add_epi32(MSG1, TMP);
      MSG1 = _mm_sha256msg2_epu32(MSG1, MSG0);
      MSG = _mm_shuffle_epi32(MSG, 0x0E);
      STATE0 = _mm_sha256rnds2_epu32(STATE0, STATE1, MSG);
      MSG3 = _mm_sha256msg1_epu32(MSG3, MSG0);
  
      /* Rounds 52-55 */
      MSG = _mm_add_epi32(MSG1, _mm_set_epi64x(
                              0x682E6FF35B9CCA4FULL, 0x4ED8AA4A391C0CB3ULL));
      STATE1 = _mm_sha256rnds2_epu32(STATE1, STATE0, MSG);
      TMP = _mm_alignr_epi8(MSG1, MSG0, 4);
      MSG2 = _mm_add_epi32(MSG2, TMP);
      MSG2 = _mm_sha256msg2_epu32(MSG2, MSG1);
      MSG = _mm_shuffle_epi32(MSG, 0x0E);
      STATE0 = _mm_sha256rnds2_epu32(STATE0, STATE1, MSG);
  
      /* Rounds 56-59 */
      MSG = _mm_add_epi32(MSG2, _mm_set_epi64x(
                              0x8CC7020884C87814ULL, 0x78A5636F748F82EEULL));
      STATE1 = _mm_sha256rnds2_epu32(STATE1, STATE0, MSG);
      TMP = _mm_alignr_epi8(MSG2, MSG1, 4);
      MSG3 = _mm_add_epi32(MSG3, TMP);
      MSG3 = _mm_sha256msg2_epu32(MSG3, MSG2);
      MSG = _mm_shuffle_epi32(MSG, 0x0E);
      STATE0 = _mm_sha256rnds2_epu32(STATE0, STATE1, MSG);
  
      /* Rounds 60-63 */
      MSG = _mm_add_epi32(MSG3, _mm_set_epi64x(
                              0xC67178F2BEF9A3F7ULL, 0xA4506CEB90BEFFFAULL));
      STATE1 = _mm_sha256rnds2_epu32(STATE1, STATE0, MSG);
      MSG = _mm_shuffle_epi32(MSG, 0x0E);
      STATE0 = _mm_sha256rnds2_epu32(STATE0, STATE1, MSG);
  
      /* Combine state */
      core[0] = _mm_add_epi32(STATE0, core[0]);
      core[1] = _mm_add_epi32(STATE1, core[1]);
  }
  
  typedef struct sha256_ni {
      /*
       * These two vectors store the 8 words of the SHA-256 state, but
       * not in the same order they appear in the spec: the first word
       * holds A,B,E,F and the second word C,D,G,H.
       */
      __m128i core[2];
      sha256_block blk;
      void *pointer_to_free;
      BinarySink_IMPLEMENTATION;
      ssh_hash hash;
  } sha256_ni;
  
  static void sha256_ni_write(BinarySink *bs, const void *vp, size_t len);
  
  static sha256_ni *sha256_ni_alloc(void)
  {
      /*
       * The __m128i variables in the context structure need to be
       * 16-byte aligned, but not all malloc implementations that this
       * code has to work with will guarantee to return a 16-byte
       * aligned pointer. So we over-allocate, manually realign the
       * pointer ourselves, and store the original one inside the
       * context so we know how to free it later.
       */
      void *allocation = smalloc(sizeof(sha256_ni) + 15);
      uintptr_t alloc_address = (uintptr_t)allocation;
      uintptr_t aligned_address = (alloc_address + 15) & ~15;
      sha256_ni *s = (sha256_ni *)aligned_address;
      s->pointer_to_free = allocation;
      return s;
  }
  
  static ssh_hash *sha256_ni_new(const ssh_hashalg *alg)
  {
      if (!sha256_hw_available_cached())
          return NULL;
  
      sha256_ni *s = sha256_ni_alloc();
  
      s->hash.vt = alg;
      BinarySink_INIT(s, sha256_ni_write);
      BinarySink_DELEGATE_INIT(&s->hash, s);
  
      return &s->hash;
  }
  
  FUNC_ISA static void sha256_ni_reset(ssh_hash *hash)
  {
      sha256_ni *s = container_of(hash, sha256_ni, hash);
  
      /* Initialise the core vectors in their storage order */
      s->core[0] = _mm_set_epi64x(
          0x6a09e667bb67ae85ULL, 0x510e527f9b05688cULL);
      s->core[1] = _mm_set_epi64x(
          0x3c6ef372a54ff53aULL, 0x1f83d9ab5be0cd19ULL);
  
      sha256_block_setup(&s->blk);
  }
  
  static void sha256_ni_copyfrom(ssh_hash *hcopy, ssh_hash *horig)
  {
      sha256_ni *copy = container_of(hcopy, sha256_ni, hash);
      sha256_ni *orig = container_of(horig, sha256_ni, hash);
  
      void *ptf_save = copy->pointer_to_free;
      *copy = *orig; /* structure copy */
      copy->pointer_to_free = ptf_save;
  
      BinarySink_COPIED(copy);
      BinarySink_DELEGATE_INIT(&copy->hash, copy);
  }
  
  static void sha256_ni_free(ssh_hash *hash)
  {
      sha256_ni *s = container_of(hash, sha256_ni, hash);
  
      void *ptf = s->pointer_to_free;
      smemclr(s, sizeof(*s));
      sfree(ptf);
  }
  
  static void sha256_ni_write(BinarySink *bs, const void *vp, size_t len)
  {
      sha256_ni *s = BinarySink_DOWNCAST(bs, sha256_ni);
  
      while (len > 0)
          if (sha256_block_write(&s->blk, &vp, &len))
              sha256_ni_block(s->core, s->blk.block);
  }
  
  FUNC_ISA static void sha256_ni_digest(ssh_hash *hash, uint8_t *digest)
  {
      sha256_ni *s = container_of(hash, sha256_ni, hash);
  
      sha256_block_pad(&s->blk, BinarySink_UPCAST(s));
  
      /* Rearrange the words into the output order */
      __m128i feba = _mm_shuffle_epi32(s->core[0], 0x1B);
      __m128i dchg = _mm_shuffle_epi32(s->core[1], 0xB1);
      __m128i dcba = _mm_blend_epi16(feba, dchg, 0xF0);
      __m128i hgfe = _mm_alignr_epi8(dchg, feba, 8);
  
      /* Byte-swap them into the output endianness */
      const __m128i mask = _mm_setr_epi8(3,2,1,0,7,6,5,4,11,10,9,8,15,14,13,12);
      dcba = _mm_shuffle_epi8(dcba, mask);
      hgfe = _mm_shuffle_epi8(hgfe, mask);
  
      /* And store them */
      __m128i *output = (__m128i *)digest;
      _mm_storeu_si128(output, dcba);
      _mm_storeu_si128(output+1, hgfe);
  }
  
  const ssh_hashalg ssh_sha256_hw = {
      .new = sha256_ni_new,
      .reset = sha256_ni_reset,
      .copyfrom = sha256_ni_copyfrom,
      .digest = sha256_ni_digest,
      .free = sha256_ni_free,
      .hlen = 32,
      .blocklen = 64,
      HASHALG_NAMES_ANNOTATED("SHA-256", "SHA-NI accelerated"),
  };
  
  /* ----------------------------------------------------------------------
   * Hardware-accelerated implementation of SHA-256 using Arm NEON.
   */
  
  #elif HW_SHA256 == HW_SHA256_NEON
  
  /*
   * Manually set the target architecture, if we decided above that we
   * need to.
   */
  #ifdef USE_CLANG_ATTR_TARGET_AARCH64
  /*
   * A spot of cheating: redefine some ACLE feature macros before
   * including arm_neon.h. Otherwise we won't get the SHA intrinsics
   * defined by that header, because it will be looking at the settings
   * for the whole translation unit rather than the ones we're going to
   * put on some particular functions using __attribute__((target)).
   */
  #define __ARM_NEON 1
  #define __ARM_FEATURE_CRYPTO 1
  #define FUNC_ISA __attribute__ ((target("neon,crypto")))
  #endif /* USE_CLANG_ATTR_TARGET_AARCH64 */
  
  #ifndef FUNC_ISA
  #define FUNC_ISA
  #endif
  
  #ifdef USE_ARM64_NEON_H
  #include <arm64_neon.h>
  #else
  #include <arm_neon.h>
  #endif
  
  static bool sha256_hw_available(void)
  {
      /*
       * For Arm, we delegate to a per-platform detection function (see
       * explanation in sshaes.c).
       */
      return platform_sha256_hw_available();
  }
  
  typedef struct sha256_neon_core sha256_neon_core;
  struct sha256_neon_core {
      uint32x4_t abcd, efgh;
  };
  
  FUNC_ISA
  static inline uint32x4_t sha256_neon_load_input(const uint8_t *p)
  {
      return vreinterpretq_u32_u8(vrev32q_u8(vld1q_u8(p)));
  }
  
  FUNC_ISA
  static inline uint32x4_t sha256_neon_schedule_update(
      uint32x4_t m4, uint32x4_t m3, uint32x4_t m2, uint32x4_t m1)
  {
      return vsha256su1q_u32(vsha256su0q_u32(m4, m3), m2, m1);
  }
  
  FUNC_ISA
  static inline sha256_neon_core sha256_neon_round4(
      sha256_neon_core old, uint32x4_t sched, unsigned round)
  {
      sha256_neon_core new;
  
      uint32x4_t round_input = vaddq_u32(
          sched, vld1q_u32(sha256_round_constants + round));
      new.abcd = vsha256hq_u32 (old.abcd, old.efgh, round_input);
      new.efgh = vsha256h2q_u32(old.efgh, old.abcd, round_input);
      return new;
  }
  
  FUNC_ISA
  static inline void sha256_neon_block(sha256_neon_core *core, const uint8_t *p)
  {
      uint32x4_t s0, s1, s2, s3;
      sha256_neon_core cr = *core;
  
      s0 = sha256_neon_load_input(p);
      cr = sha256_neon_round4(cr, s0, 0);
      s1 = sha256_neon_load_input(p+16);
      cr = sha256_neon_round4(cr, s1, 4);
      s2 = sha256_neon_load_input(p+32);
      cr = sha256_neon_round4(cr, s2, 8);
      s3 = sha256_neon_load_input(p+48);
      cr = sha256_neon_round4(cr, s3, 12);
      s0 = sha256_neon_schedule_update(s0, s1, s2, s3);
      cr = sha256_neon_round4(cr, s0, 16);
      s1 = sha256_neon_schedule_update(s1, s2, s3, s0);
      cr = sha256_neon_round4(cr, s1, 20);
      s2 = sha256_neon_schedule_update(s2, s3, s0, s1);
      cr = sha256_neon_round4(cr, s2, 24);
      s3 = sha256_neon_schedule_update(s3, s0, s1, s2);
      cr = sha256_neon_round4(cr, s3, 28);
      s0 = sha256_neon_schedule_update(s0, s1, s2, s3);
      cr = sha256_neon_round4(cr, s0, 32);
      s1 = sha256_neon_schedule_update(s1, s2, s3, s0);
      cr = sha256_neon_round4(cr, s1, 36);
      s2 = sha256_neon_schedule_update(s2, s3, s0, s1);
      cr = sha256_neon_round4(cr, s2, 40);
      s3 = sha256_neon_schedule_update(s3, s0, s1, s2);
      cr = sha256_neon_round4(cr, s3, 44);
      s0 = sha256_neon_schedule_update(s0, s1, s2, s3);
      cr = sha256_neon_round4(cr, s0, 48);
      s1 = sha256_neon_schedule_update(s1, s2, s3, s0);
      cr = sha256_neon_round4(cr, s1, 52);
      s2 = sha256_neon_schedule_update(s2, s3, s0, s1);
      cr = sha256_neon_round4(cr, s2, 56);
      s3 = sha256_neon_schedule_update(s3, s0, s1, s2);
      cr = sha256_neon_round4(cr, s3, 60);
  
      core->abcd = vaddq_u32(core->abcd, cr.abcd);
      core->efgh = vaddq_u32(core->efgh, cr.efgh);
  }
  
  typedef struct sha256_neon {
      sha256_neon_core core;
      sha256_block blk;
      BinarySink_IMPLEMENTATION;
      ssh_hash hash;
  } sha256_neon;
  
  static void sha256_neon_write(BinarySink *bs, const void *vp, size_t len);
  
  static ssh_hash *sha256_neon_new(const ssh_hashalg *alg)
  {
      if (!sha256_hw_available_cached())
          return NULL;
  
      sha256_neon *s = snew(sha256_neon);
  
      s->hash.vt = alg;
      BinarySink_INIT(s, sha256_neon_write);
      BinarySink_DELEGATE_INIT(&s->hash, s);
      return &s->hash;
  }
  
  static void sha256_neon_reset(ssh_hash *hash)
  {
      sha256_neon *s = container_of(hash, sha256_neon, hash);
  
      s->core.abcd = vld1q_u32(sha256_initial_state);
      s->core.efgh = vld1q_u32(sha256_initial_state + 4);
  
      sha256_block_setup(&s->blk);
  }
  
  static void sha256_neon_copyfrom(ssh_hash *hcopy, ssh_hash *horig)
  {
      sha256_neon *copy = container_of(hcopy, sha256_neon, hash);
      sha256_neon *orig = container_of(horig, sha256_neon, hash);
  
      *copy = *orig; /* structure copy */
  
      BinarySink_COPIED(copy);
      BinarySink_DELEGATE_INIT(&copy->hash, copy);
  }
  
  static void sha256_neon_free(ssh_hash *hash)
  {
      sha256_neon *s = container_of(hash, sha256_neon, hash);
      smemclr(s, sizeof(*s));
      sfree(s);
  }
  
  static void sha256_neon_write(BinarySink *bs, const void *vp, size_t len)
  {
      sha256_neon *s = BinarySink_DOWNCAST(bs, sha256_neon);
  
      while (len > 0)
          if (sha256_block_write(&s->blk, &vp, &len))
              sha256_neon_block(&s->core, s->blk.block);
  }
  
  static void sha256_neon_digest(ssh_hash *hash, uint8_t *digest)
  {
      sha256_neon *s = container_of(hash, sha256_neon, hash);
  
      sha256_block_pad(&s->blk, BinarySink_UPCAST(s));
      vst1q_u8(digest,      vrev32q_u8(vreinterpretq_u8_u32(s->core.abcd)));
      vst1q_u8(digest + 16, vrev32q_u8(vreinterpretq_u8_u32(s->core.efgh)));
  }
  
  const ssh_hashalg ssh_sha256_hw = {
      .new = sha256_neon_new,
      .reset = sha256_neon_reset,
      .copyfrom = sha256_neon_copyfrom,
      .digest = sha256_neon_digest,
      .free = sha256_neon_free,
      .hlen = 32,
      .blocklen = 64,
      HASHALG_NAMES_ANNOTATED("SHA-256", "NEON accelerated"),
  };
  
  /* ----------------------------------------------------------------------
   * Stub functions if we have no hardware-accelerated SHA-256. In this
   * case, sha256_hw_new returns NULL (though it should also never be
   * selected by sha256_select, so the only thing that should even be
   * _able_ to call it is testcrypt). As a result, the remaining vtable
   * functions should never be called at all.
   */
  
  #elif HW_SHA256 == HW_SHA256_NONE
  
  static bool sha256_hw_available(void)
  {
      return false;
  }
  
  static ssh_hash *sha256_stub_new(const ssh_hashalg *alg)
  {
      return NULL;
  }
  
  #define STUB_BODY { unreachable("Should never be called"); }
  
  static void sha256_stub_reset(ssh_hash *hash) STUB_BODY
  static void sha256_stub_copyfrom(ssh_hash *hash, ssh_hash *orig) STUB_BODY
  static void sha256_stub_free(ssh_hash *hash) STUB_BODY
  static void sha256_stub_digest(ssh_hash *hash, uint8_t *digest) STUB_BODY
  
  const ssh_hashalg ssh_sha256_hw = {
      .new = sha256_stub_new,
      .reset = sha256_stub_reset,
      .copyfrom = sha256_stub_copyfrom,
      .digest = sha256_stub_digest,
      .free = sha256_stub_free,
      .hlen = 32,
      .blocklen = 64,
      HASHALG_NAMES_ANNOTATED("SHA-256", "!NONEXISTENT ACCELERATED VERSION!"),
  };
  
  #endif /* HW_SHA256 */
  