Fossil

** buffer is not a multiple of 4 bytes length, compute the sum that would
** have occurred if the buffer was padded with zeros to the next multiple
** of four bytes.
*/
static unsigned int checksum(const char *zIn, size_t N){
  static const int byteOrderTest = 1;
  const unsigned char *z = (const unsigned char *)zIn;
  const unsigned char *zEnd = (const unsigned char*)&zIn[N&~3];
  unsigned sum = 0;
  if( N>0 ){
    const unsigned char *zEnd = (const unsigned char*)&zIn[N&~3];
  assert( (z - (const unsigned char*)0)%4==0 );  /* Four-byte alignment */
  if( 0==*(char*)&byteOrderTest ){
    /* This is a big-endian machine */
    while( z<zEnd ){
      sum += *(unsigned*)z;
      z += 4;
    }
  }else{
    /* A little-endian machine */
#if GCC_VERSION>=4003000
    while( z<zEnd ){
      sum += __builtin_bswap32(*(unsigned*)z);
      z += 4;
    }
#elif defined(_MSC_VER) && _MSC_VER>=1300
    while( z<zEnd ){
      sum += _byteswap_ulong(*(unsigned*)z);
      z += 4;
    }
#else
    unsigned sum0 = 0;
    unsigned sum1 = 0;
    unsigned sum2 = 0;
    while(N >= 16){
      sum0 += ((unsigned)z[0] + z[4] + z[8] + z[12]);
      sum1 += ((unsigned)z[1] + z[5] + z[9] + z[13]);
      sum2 += ((unsigned)z[2] + z[6] + z[10]+ z[14]);
      sum  += ((unsigned)z[3] + z[7] + z[11]+ z[15]);
      z += 16;
      N -= 16;
    }
    while(N >= 4){
      sum0 += z[0];
      sum1 += z[1];
      sum2 += z[2];
      sum  += z[3];
      z += 4;
      N -= 4;
    }
    sum += (sum2 << 8) + (sum1 << 16) + (sum0 << 24);
#endif
  }
  switch(N&3){
    case 3:   sum += (z[2] << 8);
    case 2:   sum += (z[1] << 16);
    case 1:   sum += (z[0] << 24);
    default:  ;
    assert( (z - (const unsigned char*)0)%4==0 );  /* Four-byte alignment */
    if( 0==*(char*)&byteOrderTest ){
      /* This is a big-endian machine */
      while( z<zEnd ){
        sum += *(unsigned*)z;
        z += 4;
      }
    }else{
      /* A little-endian machine */
  #if GCC_VERSION>=4003000
      while( z<zEnd ){
        sum += __builtin_bswap32(*(unsigned*)z);
        z += 4;
      }
  #elif defined(_MSC_VER) && _MSC_VER>=1300
      while( z<zEnd ){
        sum += _byteswap_ulong(*(unsigned*)z);
        z += 4;
      }
  #else
      unsigned sum0 = 0;
      unsigned sum1 = 0;
      unsigned sum2 = 0;
      while(N >= 16){
        sum0 += ((unsigned)z[0] + z[4] + z[8] + z[12]);
        sum1 += ((unsigned)z[1] + z[5] + z[9] + z[13]);
        sum2 += ((unsigned)z[2] + z[6] + z[10]+ z[14]);
        sum  += ((unsigned)z[3] + z[7] + z[11]+ z[15]);
        z += 16;
        N -= 16;
      }
      while(N >= 4){
        sum0 += z[0];
        sum1 += z[1];
        sum2 += z[2];
        sum  += z[3];
        z += 4;
        N -= 4;
      }
      sum += (sum2 << 8) + (sum1 << 16) + (sum0 << 24);
  #endif
    }
    switch(N&3){
      case 3:   sum += (z[2] << 8);
      case 2:   sum += (z[1] << 16);
      case 1:   sum += (z[0] << 24);
      default:  ;
    }
  }
  return sum;
}

/*
** Create a new delta.
**