FreeCalypso > hg > freecalypso-reveng

annotate fluid-mnf/lzdecode.c @ 347:21d38dce4d15

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fluid-mnf: removed silly wait for RETURN from no-arguments display
author Mychaela Falconia <falcon@freecalypso.org>
date Fri, 13 Mar 2020 06:27:15 +0000
parents 9cecc930d78f
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
311
9cecc930d78f fluid-mnf: original source from TI,
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1 /*******************************************************************************
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2 *
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3 * Simple LZ77 compressor (c) Texas Instruments, Jesper Pedersem TI-DK
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4 *
9cecc930d78f fluid-mnf: original source from TI,
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5 * File format:
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6 * ---------------------------------------------------
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7 * | Tag | Data | Tag | Data | Tag | Data etc...
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8 * ---------------------------------------------------
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9 *
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10 * Where TAG is 1 bit indicating how to interpret the following data
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11 * (0 = uncompressed, 1 = compressed)
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12 *
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13 * Depending on TAG the Data is:
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14 * 0 : One uncompressed char of raw data
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15 * 1 : A length of and a pointer to a match in the previous data
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16 *
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17 * ----------------------------------------
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18 * Length + pointer = | Length (3 bits) | Position (12 bits) |
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19 * ----------------------------------------
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20 * MSB LSB MSB LSB
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21 *
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22 * Compression threshold is 1 i.e. add 1 to Length to get the actual Length.
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23 *
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24 * It has been found that 5+14 bits is the most optimum for our kind of
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25 * data, but we use only 3+12 bits for improoved speed. Compression is
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26 * almost as good because we can set the threshold at 1 instead of 2 (2 char
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27 * matches can be compressed to 12+3 bits)
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28 *
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29 * With a 12 bit position we can use 4K for the sliding window. Position
9cecc930d78f fluid-mnf: original source from TI,
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30 * indicates where the match exists as an absolute address into the
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31 * window. This way we have a very simple "pseudo sliding window" which
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32 * automatically enables RLE (Run Length Encoding).
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33 *
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34 * The code performs a "lazy" string search i.e. a match will be dropped if
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35 * it prevents an even greater match for the very next string. This yeild
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36 * slightly better compression (approx. 1%) at minor cost of compression
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37 * speed - decompression time is the same! A second order lazy match could
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38 * be implemented, but it gives an insignificant improovement of about 0.1%
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39 * when compressing executeables
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40 *
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41 ******************************************************************************/
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42
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43 #if (TARGET == 0)
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44 #include "fluid.h"
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45 #include <stdlib.h>
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46 #endif
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47
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48 #include "lz.h"
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49
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50
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51 /******************************************************************************
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52 * Globals
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53 ******************************************************************************/
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54
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55
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56 /******************************************************************************
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57 * getchar/putchar
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58 ******************************************************************************/
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59
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60 #define EOF -1
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61
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62 #define LZ_PUTCHAR(data) \
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63 *plz->buffer_out++ = data; \
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64 plz->buffer_out_size++;
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65
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66
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67
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68 /******************************************************************************
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69 * Code
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70 ******************************************************************************/
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71 uint8 get_byte(struct lz_s *plz)
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72 {
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73 plz->buffer_in_size--;
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74 return(*plz->buffer_in++);
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75 }
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76
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77 uint16 get_word(struct lz_s *plz)
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78 {
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79 uint16 tmp;
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80
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81 tmp = (*plz->buffer_in++) << 8;
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82 tmp |= (*plz->buffer_in++);
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83 plz->buffer_in_size -= 2;
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84 return(tmp);
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85 }
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86
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87
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88 void decompress_init(struct lz_s *plz)
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89 {
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90 plz->window_pos = 0;
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91 plz->bitbuf = 0;
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92 plz->bitbuf_size = 0;
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93 }
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94
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95 int decompress(struct lz_s *plz,
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96 unsigned char *outbuf, unsigned char *inbuf, int size)
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97 {
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98 int16 match_pos;
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99 int16 match_len, i;
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100 int8 ch;
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101 uint8 tag_byte;
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102 uint8 tag_pos;
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103 uint16 tmp;
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104
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105
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106 plz->buffer_out = outbuf;
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107 plz->buffer_out_size = 0;
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108 plz->buffer_in = inbuf;
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109 plz->buffer_in_size = size;
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110
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111 while(plz->buffer_in_size > 0)
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112 {
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113 tag_byte = get_byte(plz);
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114
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115 for(tag_pos = 0x80; (plz->buffer_in_size > 0) && (tag_pos > 0x00); tag_pos >>= 0x01)
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116 {
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117 if(tag_byte & tag_pos) // Compressed?
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118 {
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119 tmp = get_word(plz);
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120 match_len = (tmp >> POS_BITS) + THRESHOLD + 1;
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121 match_pos = (tmp & POS_MASK);
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122 for (i = 0; i < match_len; i++)
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123 {
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124 plz->window[plz->window_pos] = plz->window[WINDOW_MASK & (match_pos + i)];
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125 LZ_PUTCHAR(plz->window[plz->window_pos]);
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126 plz->window_pos++;
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127 plz->window_pos &= WINDOW_MASK;
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128 }
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129 }
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130 else
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131 {
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132 ch = get_byte(plz);
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133 plz->window[plz->window_pos] = ch;
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134 LZ_PUTCHAR(ch);
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135 plz->window_pos++;
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136 plz->window_pos &= WINDOW_MASK;
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137 }
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138 }
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139 }
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140 return plz->buffer_out_size;
9cecc930d78f fluid-mnf: original source from TI,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
141 }
9cecc930d78f fluid-mnf: original source from TI,
Mychaela Falconia <falcon@freecalypso.org>
parents:
diff changeset
142