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Overview
Comment:Use intrinsic byte-swapping functions to boost the performance of delta checksums.
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SHA1: 7338b3a9510281e7d49643f55a5c27c24107f083
User & Date: drh 2015-12-31 15:45:10
Context
2015-12-31
15:46
Add MIME types for C# and VB.NET. check-in: 5e81f4c0 user: drh tags: trunk
15:45
Use intrinsic byte-swapping functions to boost the performance of delta checksums. check-in: 7338b3a9 user: drh tags: trunk
15:44
Update the built-in SQLite to 3.10.0 beta for SQLite testing. check-in: ec8394e1 user: drh tags: trunk
15:18
Use intrinsic functions to boost the performance of the delta checksum. Closed-Leaf check-in: 726ab361 user: drh tags: checksum-intrinsics
Changes
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Changes to src/delta.c.

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*/
static int digit_count(int v){
  unsigned int i, x;
  for(i=1, x=64; v>=x; i++, x <<= 6){}
  return i;
}







/*
** Compute a 32-bit checksum on the N-byte buffer.  Return the result.



*/
static unsigned int checksum(const char *zIn, size_t N){

  const unsigned char *z = (const unsigned char *)zIn;






















  unsigned sum0 = 0;
  unsigned sum1 = 0;
  unsigned sum2 = 0;
  unsigned sum3 = 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]);
    sum3 += ((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];
    sum3 += z[3];
    z += 4;
    N -= 4;
  }
  sum3 += (sum2 << 8) + (sum1 << 16) + (sum0 << 24);


  switch(N){
    case 3:   sum3 += (z[2] << 8);
    case 2:   sum3 += (z[1] << 16);
    case 1:   sum3 += (z[0] << 24);
    default:  ;
  }
  return sum3;
}

/*
** Create a new delta.
**
** The delta is written into a preallocated buffer, zDelta, which
** should be at least 60 bytes longer than the target file, zOut.







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*/
static int digit_count(int v){
  unsigned int i, x;
  for(i=1, x=64; v>=x; i++, x <<= 6){}
  return i;
}

#ifdef __GNUC__
# define GCC_VERSION (__GNUC__*1000000+__GNUC_MINOR__*1000+__GNUC_PATCHLEVEL__)
#else
# define GCC_VERSION 0
#endif

/*
** Compute a 32-bit big-endian checksum on the N-byte buffer.  If the
** 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;
  assert( (3&(sqlite3_uint64)z)==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.
**
** The delta is written into a preallocated buffer, zDelta, which
** should be at least 60 bytes longer than the target file, zOut.