core/rllpack.c

   1 /* ----------------------------------------------------------------------- *
   2  *
   3  *   Copyright 2007-2009 H. Peter Anvin - All Rights Reserved
   4  *   Copyright 2009 Intel Corporation; author: H. Peter Anvin
   5  *
   6  *   This program is free software; you can redistribute it and/or modify
   7  *   it under the terms of the GNU General Public License as published by
   8  *   the Free Software Foundation, Inc., 51 Franklin St, Fifth Floor,
   9  *   Boston MA 02110-1301, USA; either version 2 of the License, or
  10  *   (at your option) any later version; incorporated herein by reference.
  11  *
  12  * ----------------------------------------------------------------------- */
  13
  14 /*
  15  * rllpack.inc
  16  *
  17  * Very simple RLL compressor/decompressor, used to pack binary structures
  18  * together.
  19  *
  20  * Format of leading byte
  21  * 1-128        = x verbatim bytes follow
  22  * 129-223      = (x-126) times subsequent byte
  23  * 224-255      = (x-224)*256+(next byte) times the following byte
  24  * 0            = end of data
  25  *
  26  * These structures are stored *in reverse order* in high memory.
  27  * High memory pointers point to one byte beyond the end.
  28  */
  29
  30 #include <com32.h>
  31 #include <stddef.h>
  32 #include <string.h>
  33
  34 void rllpack(com32sys_t * regs)
  35 {
  36     uint8_t *i = (uint8_t *) (regs->esi.l);
  37     uint8_t *o = (uint8_t *) (regs->edi.l);
  38     size_t cnt = regs->ecx.l;
  39     size_t run, vrun, tcnt;
  40     uint8_t *hdr = NULL;
  41     uint8_t c;
  42
  43     vrun = (size_t)-1;
  44     while (cnt) {
  45         c = *i;
  46
  47         run = 1;
  48         tcnt = (cnt > 8191) ? 8191 : cnt;
  49         while (run < tcnt && i[run] == c)
  50             run++;
  51
  52         if (run < 3) {
  53             if (vrun >= 128) {
  54                 hdr = --o;
  55                 vrun = 0;
  56             }
  57             *--o = c;
  58             *hdr = ++vrun;
  59             i++;
  60             cnt--;
  61         } else {
  62             if (run < 224 - 126) {
  63                 *--o = run + 126;
  64             } else {
  65                 o -= 2;
  66                 *(uint16_t *) o = run + (224 << 8);
  67             }
  68             *--o = c;
  69             vrun = (size_t)-1;
  70             i += run;
  71             cnt -= run;
  72         }
  73     }
  74     *--o = 0;
  75
  76     regs->esi.l = (size_t)i;
  77     regs->edi.l = (size_t)o;
  78 }
  79
  80 void rllunpack(com32sys_t * regs)
  81 {
  82     uint8_t *i = (uint8_t *) regs->esi.l;
  83     uint8_t *o = (uint8_t *) regs->edi.l;
  84     uint8_t c;
  85     size_t n;
  86
  87     while ((c = *--i)) {
  88         if (c <= 128) {
  89             while (c--)
  90                 *o++ = *--i;
  91         } else {
  92             if (c < 224)
  93                 n = c - 126;
  94             else
  95                 n = ((c - 224) << 8) + *--i;
  96             c = *--i;
  97             while (n--)
  98                 *o++ = c;
  99         }
 100     }
 101
 102     regs->esi.l = (size_t)i;
 103     regs->ecx.l = (size_t)o - regs->edi.l;
 104     regs->edi.l = (size_t)o;
 105 }