text: #pragma once
  // clang-format off
  /*
    sha-256 implementation for MAVLink based on Heimdal sources, with
    modifications to suit mavlink headers
   */
  /*
   * Copyright (c) 1995 - 2001 Kungliga Tekniska H�gskolan
   * (Royal Institute of Technology, Stockholm, Sweden).
   * All rights reserved.
   * 
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   * 
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   * 
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in the
   *    documentation and/or other materials provided with the distribution.
   * 
   * 3. Neither the name of the Institute nor the names of its contributors
   *    may be used to endorse or promote products derived from this software
   *    without specific prior written permission.
   * 
   * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
   * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
   * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   * SUCH DAMAGE.
   */
  
  /*
    allow implementation to provide their own sha256 with the same API
  */
  #ifndef HAVE_MAVLINK_SHA256
  
  #ifdef MAVLINK_USE_CXX_NAMESPACE
  namespace mavlink {
  #endif
  
  #ifndef MAVLINK_HELPER
  #define MAVLINK_HELPER
  #endif
  
  typedef struct {
    uint32_t sz[2];
    uint32_t counter[8];
    union {
        unsigned char save_bytes[64];
        uint32_t save_u32[16];
    } u;
  } mavlink_sha256_ctx;
  
  #define Ch(x,y,z) (((x) & (y)) ^ ((~(x)) & (z)))
  #define Maj(x,y,z) (((x) & (y)) ^ ((x) & (z)) ^ ((y) & (z)))
  
  #define ROTR(x,n)   (((x)>>(n)) | ((x) << (32 - (n))))
  
  #define Sigma0(x)	(ROTR(x,2)  ^ ROTR(x,13) ^ ROTR(x,22))
  #define Sigma1(x)	(ROTR(x,6)  ^ ROTR(x,11) ^ ROTR(x,25))
  #define sigma0(x)	(ROTR(x,7)  ^ ROTR(x,18) ^ ((x)>>3))
  #define sigma1(x)	(ROTR(x,17) ^ ROTR(x,19) ^ ((x)>>10))
  
  #define A m->counter[0]
  #define B m->counter[1]
  #define C m->counter[2]
  #define D m->counter[3]
  #define E m->counter[4]
  #define F m->counter[5]
  #define G m->counter[6]
  #define H m->counter[7]
  
  static const uint32_t mavlink_sha256_constant_256[64] = {
      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
  };
  
  MAVLINK_HELPER void mavlink_sha256_init(mavlink_sha256_ctx *m)
  {
      m->sz[0] = 0;
      m->sz[1] = 0;
      A = 0x6a09e667;
      B = 0xbb67ae85;
      C = 0x3c6ef372;
      D = 0xa54ff53a;
      E = 0x510e527f;
      F = 0x9b05688c;
      G = 0x1f83d9ab;
      H = 0x5be0cd19;
  }
  
  static inline void mavlink_sha256_calc(mavlink_sha256_ctx *m, uint32_t *in)
  {
      uint32_t AA, BB, CC, DD, EE, FF, GG, HH;
      uint32_t data[64];
      int i;
  
      AA = A;
      BB = B;
      CC = C;
      DD = D;
      EE = E;
      FF = F;
      GG = G;
      HH = H;
  
      for (i = 0; i < 16; ++i)
  	data[i] = in[i];
      for (i = 16; i < 64; ++i)
  	data[i] = sigma1(data[i-2]) + data[i-7] + 
  	    sigma0(data[i-15]) + data[i - 16];
  
      for (i = 0; i < 64; i++) {
  	uint32_t T1, T2;
  
  	T1 = HH + Sigma1(EE) + Ch(EE, FF, GG) + mavlink_sha256_constant_256[i] + data[i];
  	T2 = Sigma0(AA) + Maj(AA,BB,CC);
  			     
  	HH = GG;
  	GG = FF;
  	FF = EE;
  	EE = DD + T1;
  	DD = CC;
  	CC = BB;
  	BB = AA;
  	AA = T1 + T2;
      }
  
      A += AA;
      B += BB;
      C += CC;
      D += DD;
      E += EE;
      F += FF;
      G += GG;
      H += HH;
  }
  
  MAVLINK_HELPER void mavlink_sha256_update(mavlink_sha256_ctx *m, const void *v, uint32_t len)
  {
      const unsigned char *p = (const unsigned char *)v;
      uint32_t old_sz = m->sz[0];
      uint32_t offset;
  
      m->sz[0] += len * 8;
      if (m->sz[0] < old_sz)
  	++m->sz[1];
      offset = (old_sz / 8) % 64;
      while(len > 0){
  	uint32_t l = 64 - offset;
          if (len < l) {
              l = len;
          }
  	memcpy(m->u.save_bytes + offset, p, l);
  	offset += l;
  	p += l;
  	len -= l;
  	if(offset == 64){
  	    int i;
  	    uint32_t current[16];
  	    const uint32_t *u = m->u.save_u32;
  	    for (i = 0; i < 16; i++){
                  const uint8_t *p1 = (const uint8_t *)&u[i];
                  uint8_t *p2 = (uint8_t *)&current[i];
                  p2[0] = p1[3];
                  p2[1] = p1[2];
                  p2[2] = p1[1];
                  p2[3] = p1[0];
  	    }
  	    mavlink_sha256_calc(m, current);
  	    offset = 0;
  	}
      }
  }
  
  /*
    get first 48 bits of final sha256 hash
   */
  MAVLINK_HELPER void mavlink_sha256_final_48(mavlink_sha256_ctx *m, uint8_t result[6])
  {
      unsigned char zeros[72];
      unsigned offset = (m->sz[0] / 8) % 64;
      unsigned int dstart = (120 - offset - 1) % 64 + 1;
      uint8_t *p = (uint8_t *)&m->counter[0];
      
      *zeros = 0x80;
      memset (zeros + 1, 0, sizeof(zeros) - 1);
      zeros[dstart+7] = (m->sz[0] >> 0) & 0xff;
      zeros[dstart+6] = (m->sz[0] >> 8) & 0xff;
      zeros[dstart+5] = (m->sz[0] >> 16) & 0xff;
      zeros[dstart+4] = (m->sz[0] >> 24) & 0xff;
      zeros[dstart+3] = (m->sz[1] >> 0) & 0xff;
      zeros[dstart+2] = (m->sz[1] >> 8) & 0xff;
      zeros[dstart+1] = (m->sz[1] >> 16) & 0xff;
      zeros[dstart+0] = (m->sz[1] >> 24) & 0xff;
  
      mavlink_sha256_update(m, zeros, dstart + 8);
  
      // this ordering makes the result consistent with taking the first
      // 6 bytes of more conventional sha256 functions. It assumes
      // little-endian ordering of m->counter
      result[0] = p[3];
      result[1] = p[2];
      result[2] = p[1];
      result[3] = p[0];
      result[4] = p[7];
      result[5] = p[6];
  }
  
  // prevent conflicts with users of the header
  #undef A
  #undef B
  #undef C
  #undef D
  #undef E
  #undef F
  #undef G
  #undef H
  #undef Ch
  #undef ROTR
  #undef Sigma0
  #undef Sigma1
  #undef sigma0
  #undef sigma1
  
  #ifdef MAVLINK_USE_CXX_NAMESPACE
  } // namespace mavlink
  #endif
  
  #endif // HAVE_MAVLINK_SHA256
  
  // clang-format on