TempleOS-Rijn/LT/OSMain/Compress.CPZ

// The following algorithm came from a magazine
// and I implimented it when I worked for Ticketmaster.

void ArcCompressBuf(ArcCs *c)
//Use $LK,"CompressBuf","MN:CompressBuf"$() unless you are doing
//more than one buffer.
{
  ArcTableEntry *temp,*temp1;
  U8 basecode;
  U1 *src_ptr,*src_limit,ch;

  src_ptr=c->src_buf+c->src_pos;
  src_limit=c->src_buf+c->src_size;

  if (c->saved_basecode==0xFFFFFFFF)
    basecode=*src_ptr++;
  else
    basecode=c->saved_basecode;

  while (src_ptr<src_limit &&
    c->dst_pos+c->cur_bits_in_use<=c->dst_size) {
    ArcGetTableEntry(c);

    arc_start_loop1:
      if (src_ptr>=src_limit) goto arc_done_compression;
      ch=*src_ptr++;
      if (temp=c->hash[basecode])
	do {
	  if (temp->ch==ch) {
	    basecode=(temp-&c->compress[0])>>4;
#assert sizeof(ArcTableEntry)==16

	    goto arc_start_loop1;
	  }
	} while (temp=temp->next);

    OrU4BitField(c->dst_buf,c->dst_pos,basecode);
    c->dst_pos+=c->cur_bits_in_use;

    c->entry_used=TRUE;
    temp=c->cur_entry;
    temp->basecode=basecode;
    temp->ch=ch;
    temp1=&c->hash[basecode];
    temp->next=temp1->next;
    temp1->next=temp;

    basecode=ch;
  }
arc_done_compression:
  c->saved_basecode=basecode;
  c->src_pos=src_ptr-c->src_buf;
}

void ArcFinishCompression(ArcCs *c)
{
  if (c->dst_pos+c->cur_bits_in_use<=c->dst_size) {
    OrU4BitField(c->dst_buf,c->dst_pos,c->saved_basecode);
    c->dst_pos+=c->cur_bits_in_use;
  }
}

void ArcExpandBuf(ArcCs *c)
//Use $LK,"ExpandBuf","MN:ExpandBuf"$() unless you know what
//you're doing.  I forgot why I made this
//"public".
{
  U1 *dst_ptr,*dst_limit;
  U8 basecode,lastcode,code;
  ArcTableEntry *temp,*temp1;

  dst_ptr=c->dst_buf+c->dst_pos;
  dst_limit=c->dst_buf+c->dst_size;

  while (dst_ptr<dst_limit &&
	 c->stack_ptr!=c->stack_base)
    *dst_ptr++ = * -- c->stack_ptr;

  if (c->stack_ptr==c->stack_base && dst_ptr<dst_limit) {
    if (c->saved_basecode==0xFFFFFFFF) {
      lastcode=ExtractU4BitField(c->src_buf,c->src_pos,
	 c->next_bits_in_use);
      c->src_pos+=c->next_bits_in_use;
      *dst_ptr++=lastcode;
      ArcGetTableEntry(c);
      c->last_ch=lastcode;
    } else
      lastcode=c->saved_basecode;
    while (dst_ptr<dst_limit &&
      c->src_pos+c->next_bits_in_use<=c->src_size) {
      basecode=ExtractU4BitField(c->src_buf,c->src_pos,
	 c->next_bits_in_use);
      c->src_pos+=c->next_bits_in_use;
      if (c->cur_entry==&c->compress[basecode]) {
	*c->stack_ptr++=c->last_ch;
	code=lastcode;
      } else
	code=basecode;
      while (code>=c->min_table_entry) {
	*c->stack_ptr++=c->compress[code].ch;
	code=c->compress[code].basecode;
      }
      *c->stack_ptr++=code;
      c->last_ch=code;

      c->entry_used=TRUE;
      temp=c->cur_entry;
      temp->basecode=lastcode;
      temp->ch=c->last_ch;
      temp1=&c->hash[lastcode];
      temp->next=temp1->next;
      temp1->next=temp;

      ArcGetTableEntry(c);
      while (dst_ptr<dst_limit && c->stack_ptr!=c->stack_base)
	*dst_ptr++ = * -- c->stack_ptr;
      lastcode=basecode;
    }
    c->saved_basecode=lastcode;
  }
  c->dst_pos=dst_ptr-c->dst_buf;
}

ArcCs *NewArcCs(BoolU4 expand,BoolU4 text_only)
{
  ArcCs *c;
  c=MAllocZ(sizeof(ArcCs));
  if (expand) {
    c->stack_base=MAlloc(ARC_MAX_TABLE_ENTRY+1);
    c->stack_ptr=c->stack_base;
  }
  if (text_only)
    c->min_bits=7;
  else
    c->min_bits=8;
  c->min_table_entry=1<<c->min_bits;
  c->free_index=c->min_table_entry;
  c->next_bits_in_use=c->min_bits+1;
  c->free_limit=1<<c->next_bits_in_use;
  c->saved_basecode=0xFFFFFFFF;
  c->entry_used=TRUE;
  ArcGetTableEntry(c);
  c->entry_used=TRUE;
  return c;
}

void DelArcCs(ArcCs *c)
{
  Free(c->stack_base);
  Free(c);
}


ArcCompressStruct *CompressBuf(U1 *src,U8 size,
		U8 flags=0)
{
  U8 size_out;
  ArcCompressStruct *result;
  BoolU4 text_only=(ArcDetermineCompressionType(src,size)==CT_7_BIT);
  ArcCs *c=NewArcCs(FALSE,text_only);
  c->src_size=size;
  c->src_buf=src;
  c->dst_size=(size+sizeof(ArcCompressStruct)-1)<<3;
  c->dst_buf=MAllocZ(c->dst_size>>3);
  c->dst_pos=(sizeof(ArcCompressStruct)-1)<<3;
  ArcCompressBuf(c);
  ArcFinishCompression(c);
  if (c->src_pos==c->src_size) {
    size_out=(c->dst_pos+7)>>3;
    result=MAlloc(size_out);
    MemCpy(result,c->dst_buf,size_out);
    result->compression_type=(text_only) ? CT_7_BIT:CT_8_BIT;
    result->compressed_size=size_out;
  } else {
    result=MAlloc(size+sizeof(ArcCompressStruct)-1);
    MemCpy(result->body,src,size);
    result->compression_type=CT_NONE;
    result->compressed_size=size+sizeof(ArcCompressStruct)-1;
  }
  result->expanded_size=size;
  result->flags=flags;
  Free(c->dst_buf);
  DelArcCs(c);
  return result;
}

U1 *ExpandBuf(ArcCompressStruct *r)
{
  ArcCs *c;
  U1 *result;
  BoolU4 text_only;
  result=MAlloc(r->expanded_size+1);
  result[r->expanded_size]=0; //terminate

  text_only=(r->compression_type==CT_7_BIT);
  if (r->compression_type==CT_NONE) {
    MemCpy(result,r->body,r->expanded_size);
    goto expand_end;
  }
  c=NewArcCs(TRUE,text_only);
  c->src_size=r->compressed_size<<3;
  c->src_pos=(sizeof(ArcCompressStruct)-1)<<3;
  c->src_buf=r;
  c->dst_size=r->expanded_size;
  c->dst_buf=result;
  c->dst_pos=0;
  ArcExpandBuf(c);
  DelArcCs(c);

expand_end:
  return result;
}