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1 /* inffast.c -- fast decoding |
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2 * Copyright (C) 1995-2004 Mark Adler |
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3 * For conditions of distribution and use, see copyright notice in zlib.h |
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4 */ |
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5 |
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6 #include "zutil.h" |
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7 #include "inftrees.h" |
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8 #include "inflate.h" |
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9 #include "inffast.h" |
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10 |
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11 #ifndef ASMINF |
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12 |
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13 /* Allow machine dependent optimization for post-increment or pre-increment. |
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14 Based on testing to date, |
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15 Pre-increment preferred for: |
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16 - PowerPC G3 (Adler) |
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17 - MIPS R5000 (Randers-Pehrson) |
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18 Post-increment preferred for: |
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19 - none |
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20 No measurable difference: |
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21 - Pentium III (Anderson) |
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22 - M68060 (Nikl) |
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23 */ |
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24 #ifdef POSTINC |
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25 # define OFF 0 |
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26 # define PUP(a) *(a)++ |
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27 #else |
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28 # define OFF 1 |
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29 # define PUP(a) *++(a) |
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30 #endif |
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31 |
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32 /* |
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33 Decode literal, length, and distance codes and write out the resulting |
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34 literal and match bytes until either not enough input or output is |
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35 available, an end-of-block is encountered, or a data error is encountered. |
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36 When large enough input and output buffers are supplied to inflate(), for |
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37 example, a 16K input buffer and a 64K output buffer, more than 95% of the |
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38 inflate execution time is spent in this routine. |
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39 |
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40 Entry assumptions: |
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41 |
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42 state->mode == LEN |
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43 strm->avail_in >= 6 |
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44 strm->avail_out >= 258 |
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45 start >= strm->avail_out |
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46 state->bits < 8 |
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47 |
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48 On return, state->mode is one of: |
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49 |
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50 LEN -- ran out of enough output space or enough available input |
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51 TYPE -- reached end of block code, inflate() to interpret next block |
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52 BAD -- error in block data |
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53 |
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54 Notes: |
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55 |
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56 - The maximum input bits used by a length/distance pair is 15 bits for the |
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57 length code, 5 bits for the length extra, 15 bits for the distance code, |
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58 and 13 bits for the distance extra. This totals 48 bits, or six bytes. |
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59 Therefore if strm->avail_in >= 6, then there is enough input to avoid |
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60 checking for available input while decoding. |
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61 |
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62 - The maximum bytes that a single length/distance pair can output is 258 |
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63 bytes, which is the maximum length that can be coded. inflate_fast() |
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64 requires strm->avail_out >= 258 for each loop to avoid checking for |
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65 output space. |
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66 */ |
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67 void inflate_fast(strm, start) |
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68 z_streamp strm; |
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69 unsigned start; /* inflate()'s starting value for strm->avail_out */ |
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70 { |
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71 struct inflate_state FAR *state; |
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72 unsigned char FAR *in; /* local strm->next_in */ |
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73 unsigned char FAR *last; /* while in < last, enough input available */ |
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74 unsigned char FAR *out; /* local strm->next_out */ |
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75 unsigned char FAR *beg; /* inflate()'s initial strm->next_out */ |
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76 unsigned char FAR *end; /* while out < end, enough space available */ |
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77 #ifdef INFLATE_STRICT |
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78 unsigned dmax; /* maximum distance from zlib header */ |
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79 #endif |
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80 unsigned wsize; /* window size or zero if not using window */ |
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81 unsigned whave; /* valid bytes in the window */ |
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82 unsigned write; /* window write index */ |
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83 unsigned char FAR *window; /* allocated sliding window, if wsize != 0 */ |
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84 unsigned long hold; /* local strm->hold */ |
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85 unsigned bits; /* local strm->bits */ |
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86 code const FAR *lcode; /* local strm->lencode */ |
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87 code const FAR *dcode; /* local strm->distcode */ |
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88 unsigned lmask; /* mask for first level of length codes */ |
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89 unsigned dmask; /* mask for first level of distance codes */ |
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90 code this; /* retrieved table entry */ |
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91 unsigned op; /* code bits, operation, extra bits, or */ |
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92 /* window position, window bytes to copy */ |
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93 unsigned len; /* match length, unused bytes */ |
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94 unsigned dist; /* match distance */ |
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95 unsigned char FAR *from; /* where to copy match from */ |
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96 |
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97 /* copy state to local variables */ |
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98 state = (struct inflate_state FAR *)strm->state; |
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99 in = strm->next_in - OFF; |
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100 last = in + (strm->avail_in - 5); |
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101 out = strm->next_out - OFF; |
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102 beg = out - (start - strm->avail_out); |
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103 end = out + (strm->avail_out - 257); |
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104 #ifdef INFLATE_STRICT |
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105 dmax = state->dmax; |
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106 #endif |
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107 wsize = state->wsize; |
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108 whave = state->whave; |
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109 write = state->write; |
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110 window = state->window; |
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111 hold = state->hold; |
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112 bits = state->bits; |
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113 lcode = state->lencode; |
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114 dcode = state->distcode; |
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115 lmask = (1U << state->lenbits) - 1; |
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116 dmask = (1U << state->distbits) - 1; |
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117 |
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118 /* decode literals and length/distances until end-of-block or not enough |
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119 input data or output space */ |
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120 do { |
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121 if (bits < 15) { |
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122 hold += (unsigned long)(PUP(in)) << bits; |
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123 bits += 8; |
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124 hold += (unsigned long)(PUP(in)) << bits; |
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125 bits += 8; |
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126 } |
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127 this = lcode[hold & lmask]; |
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128 dolen: |
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129 op = (unsigned)(this.bits); |
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130 hold >>= op; |
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131 bits -= op; |
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132 op = (unsigned)(this.op); |
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133 if (op == 0) { /* literal */ |
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134 Tracevv((stderr, this.val >= 0x20 && this.val < 0x7f ? |
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135 "inflate: literal '%c'\n" : |
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136 "inflate: literal 0x%02x\n", this.val)); |
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137 PUP(out) = (unsigned char)(this.val); |
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138 } |
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139 else if (op & 16) { /* length base */ |
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140 len = (unsigned)(this.val); |
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141 op &= 15; /* number of extra bits */ |
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142 if (op) { |
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143 if (bits < op) { |
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144 hold += (unsigned long)(PUP(in)) << bits; |
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145 bits += 8; |
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146 } |
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147 len += (unsigned)hold & ((1U << op) - 1); |
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148 hold >>= op; |
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149 bits -= op; |
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150 } |
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151 Tracevv((stderr, "inflate: length %u\n", len)); |
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152 if (bits < 15) { |
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153 hold += (unsigned long)(PUP(in)) << bits; |
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154 bits += 8; |
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155 hold += (unsigned long)(PUP(in)) << bits; |
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156 bits += 8; |
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157 } |
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158 this = dcode[hold & dmask]; |
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159 dodist: |
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160 op = (unsigned)(this.bits); |
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161 hold >>= op; |
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162 bits -= op; |
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163 op = (unsigned)(this.op); |
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164 if (op & 16) { /* distance base */ |
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165 dist = (unsigned)(this.val); |
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166 op &= 15; /* number of extra bits */ |
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167 if (bits < op) { |
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168 hold += (unsigned long)(PUP(in)) << bits; |
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169 bits += 8; |
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170 if (bits < op) { |
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171 hold += (unsigned long)(PUP(in)) << bits; |
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172 bits += 8; |
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173 } |
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174 } |
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175 dist += (unsigned)hold & ((1U << op) - 1); |
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176 #ifdef INFLATE_STRICT |
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177 if (dist > dmax) { |
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178 strm->msg = (char *)"invalid distance too far back"; |
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179 state->mode = BAD; |
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180 break; |
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181 } |
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182 #endif |
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183 hold >>= op; |
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184 bits -= op; |
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185 Tracevv((stderr, "inflate: distance %u\n", dist)); |
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186 op = (unsigned)(out - beg); /* max distance in output */ |
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187 if (dist > op) { /* see if copy from window */ |
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188 op = dist - op; /* distance back in window */ |
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189 if (op > whave) { |
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190 strm->msg = (char *)"invalid distance too far back"; |
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191 state->mode = BAD; |
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192 break; |
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193 } |
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194 from = window - OFF; |
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195 if (write == 0) { /* very common case */ |
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196 from += wsize - op; |
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197 if (op < len) { /* some from window */ |
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198 len -= op; |
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199 do { |
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200 PUP(out) = PUP(from); |
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201 } while (--op); |
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202 from = out - dist; /* rest from output */ |
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203 } |
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204 } |
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205 else if (write < op) { /* wrap around window */ |
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206 from += wsize + write - op; |
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207 op -= write; |
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208 if (op < len) { /* some from end of window */ |
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209 len -= op; |
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210 do { |
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211 PUP(out) = PUP(from); |
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212 } while (--op); |
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213 from = window - OFF; |
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214 if (write < len) { /* some from start of window */ |
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215 op = write; |
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216 len -= op; |
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217 do { |
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218 PUP(out) = PUP(from); |
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219 } while (--op); |
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220 from = out - dist; /* rest from output */ |
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221 } |
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222 } |
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223 } |
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224 else { /* contiguous in window */ |
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225 from += write - op; |
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226 if (op < len) { /* some from window */ |
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227 len -= op; |
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228 do { |
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229 PUP(out) = PUP(from); |
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230 } while (--op); |
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231 from = out - dist; /* rest from output */ |
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232 } |
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233 } |
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234 while (len > 2) { |
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235 PUP(out) = PUP(from); |
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236 PUP(out) = PUP(from); |
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237 PUP(out) = PUP(from); |
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238 len -= 3; |
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239 } |
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240 if (len) { |
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241 PUP(out) = PUP(from); |
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242 if (len > 1) |
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243 PUP(out) = PUP(from); |
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244 } |
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245 } |
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246 else { |
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247 from = out - dist; /* copy direct from output */ |
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248 do { /* minimum length is three */ |
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249 PUP(out) = PUP(from); |
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250 PUP(out) = PUP(from); |
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251 PUP(out) = PUP(from); |
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252 len -= 3; |
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253 } while (len > 2); |
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254 if (len) { |
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255 PUP(out) = PUP(from); |
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256 if (len > 1) |
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257 PUP(out) = PUP(from); |
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258 } |
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259 } |
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260 } |
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261 else if ((op & 64) == 0) { /* 2nd level distance code */ |
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262 this = dcode[this.val + (hold & ((1U << op) - 1))]; |
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263 goto dodist; |
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264 } |
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265 else { |
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266 strm->msg = (char *)"invalid distance code"; |
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267 state->mode = BAD; |
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268 break; |
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269 } |
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270 } |
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271 else if ((op & 64) == 0) { /* 2nd level length code */ |
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272 this = lcode[this.val + (hold & ((1U << op) - 1))]; |
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273 goto dolen; |
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274 } |
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275 else if (op & 32) { /* end-of-block */ |
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276 Tracevv((stderr, "inflate: end of block\n")); |
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277 state->mode = TYPE; |
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278 break; |
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279 } |
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280 else { |
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281 strm->msg = (char *)"invalid literal/length code"; |
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282 state->mode = BAD; |
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283 break; |
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284 } |
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285 } while (in < last && out < end); |
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286 |
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287 /* return unused bytes (on entry, bits < 8, so in won't go too far back) */ |
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288 len = bits >> 3; |
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289 in -= len; |
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290 bits -= len << 3; |
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291 hold &= (1U << bits) - 1; |
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292 |
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293 /* update state and return */ |
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294 strm->next_in = in + OFF; |
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295 strm->next_out = out + OFF; |
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296 strm->avail_in = (unsigned)(in < last ? 5 + (last - in) : 5 - (in - last)); |
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297 strm->avail_out = (unsigned)(out < end ? |
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298 257 + (end - out) : 257 - (out - end)); |
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299 state->hold = hold; |
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300 state->bits = bits; |
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301 return; |
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302 } |
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303 |
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304 /* |
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305 inflate_fast() speedups that turned out slower (on a PowerPC G3 750CXe): |
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306 - Using bit fields for code structure |
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307 - Different op definition to avoid & for extra bits (do & for table bits) |
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308 - Three separate decoding do-loops for direct, window, and write == 0 |
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309 - Special case for distance > 1 copies to do overlapped load and store copy |
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310 - Explicit branch predictions (based on measured branch probabilities) |
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311 - Deferring match copy and interspersed it with decoding subsequent codes |
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312 - Swapping literal/length else |
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313 - Swapping window/direct else |
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314 - Larger unrolled copy loops (three is about right) |
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315 - Moving len -= 3 statement into middle of loop |
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316 */ |
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317 |
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318 #endif /* !ASMINF */ |