static FASTLZ_INLINE int FASTLZ_COMPRESSOR()

in fastlz/fastlz.c [166:418]

• 192 lines of code
• 44 McCabe index (conditional complexity)

static FASTLZ_INLINE int FASTLZ_COMPRESSOR(const void* input, int length, void* output)
{
  const flzuint8* ip = (const flzuint8*) input;
  const flzuint8* ip_bound = ip + length - 2;
  const flzuint8* ip_limit = ip + length - 12;
  flzuint8* op = (flzuint8*) output;

  const flzuint8* htab[HASH_SIZE];
  const flzuint8** hslot;
  flzuint32 hval;

  flzuint32 copy;

  /* sanity check */
  if(FASTLZ_UNEXPECT_CONDITIONAL(length < 4))
  {
    if(length)
    {
      /* create literal copy only */
      *op++ = length-1;
      ip_bound++;
      while(ip <= ip_bound)
        *op++ = *ip++;
      return length+1;
    }
    else
      return 0;
  }

  /* initializes hash table */
  for (hslot = htab; hslot < htab + HASH_SIZE; hslot++)
    *hslot = ip;

  /* we start with literal copy */
  copy = 2;
  *op++ = MAX_COPY-1;
  *op++ = *ip++;
  *op++ = *ip++;

  /* main loop */
  while(FASTLZ_EXPECT_CONDITIONAL(ip < ip_limit))
  {
    const flzuint8* ref;
    flzuint32 distance;

    /* minimum match length */
    flzuint32 len = 3;

    /* comparison starting-point */
    const flzuint8* anchor = ip;

    /* check for a run */
#if FASTLZ_LEVEL==2
    if(ip[0] == ip[-1] && FASTLZ_READU16(ip-1)==FASTLZ_READU16(ip+1))
    {
      distance = 1;
      ip += 3;
      ref = anchor - 1 + 3;
      goto match;
    }
#endif

    /* find potential match */
    HASH_FUNCTION(hval,ip);
    hslot = htab + hval;
    ref = htab[hval];

    /* calculate distance to the match */
    distance = anchor - ref;

    /* update hash table */
    *hslot = anchor;

    /* is this a match? check the first 3 bytes */
    if(distance==0 || 
#if FASTLZ_LEVEL==1
    (distance >= MAX_DISTANCE) ||
#else
    (distance >= MAX_FARDISTANCE) ||
#endif
    *ref++ != *ip++ || *ref++!=*ip++ || *ref++!=*ip++)
      goto literal;

#if FASTLZ_LEVEL==2
    /* far, needs at least 5-byte match */
    if(distance >= MAX_DISTANCE)
    {
      if(*ip++ != *ref++ || *ip++!= *ref++) 
        goto literal;
      len += 2;
    }
    
    match:
#endif

    /* last matched byte */
    ip = anchor + len;

    /* distance is biased */
    distance--;

    if(!distance)
    {
      /* zero distance means a run */
      flzuint8 x = ip[-1];
      while(ip < ip_bound)
        if(*ref++ != x) break; else ip++;
    }
    else
    for(;;)
    {
      /* safe because the outer check against ip limit */
      if(*ref++ != *ip++) break;
      if(*ref++ != *ip++) break;
      if(*ref++ != *ip++) break;
      if(*ref++ != *ip++) break;
      if(*ref++ != *ip++) break;
      if(*ref++ != *ip++) break;
      if(*ref++ != *ip++) break;
      if(*ref++ != *ip++) break;
      while(ip < ip_bound)
        if(*ref++ != *ip++) break;
      break;
    }

    /* if we have copied something, adjust the copy count */
    if(copy)
      /* copy is biased, '0' means 1 byte copy */
      *(op-copy-1) = copy-1;
    else
      /* back, to overwrite the copy count */
      op--;

    /* reset literal counter */
    copy = 0;

    /* length is biased, '1' means a match of 3 bytes */
    ip -= 3;
    len = ip - anchor;

    /* encode the match */
#if FASTLZ_LEVEL==2
    if(distance < MAX_DISTANCE)
    {
      if(len < 7)
      {
        *op++ = (len << 5) + (distance >> 8);
        *op++ = (distance & 255);
      }
      else
      {
        *op++ = (7 << 5) + (distance >> 8);
        for(len-=7; len >= 255; len-= 255)
          *op++ = 255;
        *op++ = len;
        *op++ = (distance & 255);
      }
    }
    else
    {
      /* far away, but not yet in the another galaxy... */
      if(len < 7)
      {
        distance -= MAX_DISTANCE;
        *op++ = (len << 5) + 31;
        *op++ = 255;
        *op++ = distance >> 8;
        *op++ = distance & 255;
      }
      else
      {
        distance -= MAX_DISTANCE;
        *op++ = (7 << 5) + 31;
        for(len-=7; len >= 255; len-= 255)
          *op++ = 255;
        *op++ = len;
        *op++ = 255;
        *op++ = distance >> 8;
        *op++ = distance & 255;
      }
    }
#else

    if(FASTLZ_UNEXPECT_CONDITIONAL(len > MAX_LEN-2))
      while(len > MAX_LEN-2)
      {
        *op++ = (7 << 5) + (distance >> 8);
        *op++ = MAX_LEN - 2 - 7 -2; 
        *op++ = (distance & 255);
        len -= MAX_LEN-2;
      }

    if(len < 7)
    {
      *op++ = (len << 5) + (distance >> 8);
      *op++ = (distance & 255);
    }
    else
    {
      *op++ = (7 << 5) + (distance >> 8);
      *op++ = len - 7;
      *op++ = (distance & 255);
    }
#endif

    /* update the hash at match boundary */
    HASH_FUNCTION(hval,ip);
    htab[hval] = ip++;
    HASH_FUNCTION(hval,ip);
    htab[hval] = ip++;

    /* assuming literal copy */
    *op++ = MAX_COPY-1;

    continue;

    literal:
      *op++ = *anchor++;
      ip = anchor;
      copy++;
      if(FASTLZ_UNEXPECT_CONDITIONAL(copy == MAX_COPY))
      {
        copy = 0;
        *op++ = MAX_COPY-1;
      }
  }

  /* left-over as literal copy */
  ip_bound++;
  while(ip <= ip_bound)
  {
    *op++ = *ip++;
    copy++;
    if(copy == MAX_COPY)
    {
      copy = 0;
      *op++ = MAX_COPY-1;
    }
  }

  /* if we have copied something, adjust the copy length */
  if(copy)
    *(op-copy-1) = copy-1;
  else
    op--;

#if FASTLZ_LEVEL==2
  /* marker for fastlz2 */
  *(flzuint8*)output |= (1 << 5);
#endif

  return op - (flzuint8*)output;
}