expand_bits

SFL
Version 2.11

`expand_bits`

#include "sflcomp.h"
word
expand_bits (
    const byte *src,
    byte *dst,
    word src_size)

Synopsis

Expands a block of data previously compressed using the compress bits() function. The compressed block is passed in src; the expanded result in dst. Dst must be large enough to accomodate the largest possible decompressed block. Returns the size of the expanded data.

Source Code - (sflcomp.c)

{
    word
        dst_size,                       /*  Size of expanded data            */
        src_scan,                       /*  Scan through source data         */
        length;                         /*  Size of the run or string        */
    byte
        cur_byte;                       /*  Next byte to process             */

    src_scan = 0;
    dst_size = 0;
    while (src_scan < src_size)
      {
        cur_byte = src [src_scan++];

        if (cur_byte < 8)               /*  Single bit in position 0 to 7    */
            dst [dst_size++] = 1 << cur_byte;
        else
        if (cur_byte < 128)             /*  String of 1 to 120 bytes         */
          {
            length = (word) cur_byte - 7;
            memcpy (dst + dst_size, src + src_scan, length);
            src_scan += length;
            dst_size += length;
          }
        else                            /*  Run of 1 or more bytes           */
          {
            switch (cur_byte)
              {
                case 0x80:              /*  381-2^16 binary zeroes           */
                    length   = src [src_scan++];
                    length  += src [src_scan++] << 8;
                    cur_byte = 0;
                    break;
                case 0x81:
                    length = src [src_scan++];
                    if (length == 0xFE) /*  4-255 non-zero bytes             */
                      {
                        length   = src [src_scan++];
                        cur_byte = src [src_scan++];
                      }
                    else
                    if (length == 0xFF) /*  Run of 256-2^15 non-zero bytes   */
                      {
                        length   = src [src_scan++];
                        length  += src [src_scan++] << 8;
                        cur_byte = src [src_scan++];
                      }
                    else
                      {
                        length  += 127;
                        cur_byte = 0;   /*  127 to 380 zeroes                */
                      }
                    break;
                default:                /*  1 to 126 zeroes                  */
                    length   = (cur_byte - 1) & 127;
                    cur_byte = 0;
              }
            memset (dst + dst_size, cur_byte, length);
            dst_size += length;
          }
      }
    return (dst_size);                  /*  Return expanded data size        */
}

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