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1 /* |
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2 bdiff.c - efficient binary diff extension for Mercurial |
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3 |
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4 Copyright 2005 Matt Mackall <mpm@selenic.com> |
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5 |
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6 This software may be used and distributed according to the terms of |
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7 the GNU General Public License, incorporated herein by reference. |
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8 |
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9 Based roughly on Python difflib |
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10 */ |
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11 |
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12 #include <Python.h> |
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13 #include <stdlib.h> |
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14 #include <string.h> |
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15 #include <netinet/in.h> |
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16 #include <sys/types.h> |
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17 |
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18 struct line { |
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19 int h, len, n; |
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20 const char *l; |
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21 }; |
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22 |
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23 struct hunk { |
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24 int a1, a2, b1, b2; |
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25 }; |
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26 |
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27 struct hunklist { |
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28 struct hunk *base, *head; |
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29 }; |
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30 |
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31 static inline uint32_t rol32(uint32_t word, unsigned int shift) |
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32 { |
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33 return (word << shift) | (word >> (32 - shift)); |
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34 } |
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35 |
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36 int splitlines(const char *a, int len, struct line **lr) |
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37 { |
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38 int h, i; |
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39 const char *p, *b = a; |
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40 struct line *l; |
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41 |
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42 /* count the lines */ |
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43 i = 1; /* extra line for sentinel */ |
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44 for (p = a; p < a + len; p++) |
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45 if (*p == '\n' || p == a + len - 1) |
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46 i++; |
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47 |
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48 *lr = l = malloc(sizeof(struct line) * i); |
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49 if (!l) |
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50 return -1; |
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51 |
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52 /* build the line array and calculate hashes */ |
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53 h = 0; |
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54 for (p = a; p < a + len; p++) { |
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55 h = *p + rol32(h, 7); /* a simple hash from GNU diff */ |
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56 if (*p == '\n' || p == a + len - 1) { |
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57 l->len = p - b + 1; |
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58 l->h = h; |
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59 l->l = b; |
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60 l->n = -1; |
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61 l++; |
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62 b = p + 1; |
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63 h = 0; |
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64 } |
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65 } |
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66 |
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67 /* set up a sentinel */ |
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68 l->h = l->len = 0; |
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69 l->l = a + len; |
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70 return i - 1; |
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71 } |
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72 |
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73 int inline cmp(struct line *a, struct line *b) |
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74 { |
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75 return a->len != b->len || memcmp(a->l, b->l, a->len); |
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76 } |
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77 |
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78 static int equatelines(struct line *a, int an, struct line *b, int bn) |
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79 { |
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80 int i, j, buckets = 1, t, *h, *l; |
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81 |
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82 /* build a hash table of the next highest power of 2 */ |
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83 while (buckets < bn + 1) |
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84 buckets *= 2; |
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85 |
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86 h = malloc(buckets * sizeof(int)); |
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87 l = calloc(buckets, sizeof(int)); |
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88 buckets = buckets - 1; |
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89 if (!h || !l) { |
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90 free(h); |
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91 return 0; |
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92 } |
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93 |
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94 /* clear the hash table */ |
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95 for (i = 0; i <= buckets; i++) |
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96 h[i] = -1; |
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97 |
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98 /* add lines to the hash table chains */ |
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99 for (i = bn - 1; i >= 0; i--) { |
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100 /* find the equivalence class */ |
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101 for (j = b[i].h & buckets; h[j] != -1; j = (j + 1) & buckets) |
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102 if (!cmp(b + i, b + h[j])) |
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103 break; |
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104 |
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105 /* add to the head of the equivalence class */ |
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106 b[i].n = h[j]; |
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107 b[i].h = j; |
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108 h[j] = i; |
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109 l[j]++; /* keep track of popularity */ |
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110 } |
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111 |
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112 /* compute popularity threshold */ |
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113 t = (bn >= 200) ? bn / 100 : bn + 1; |
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114 |
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115 /* match items in a to their equivalence class in b */ |
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116 for (i = 0; i < an; i++) { |
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117 /* find the equivalence class */ |
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118 for (j = a[i].h & buckets; h[j] != -1; j = (j + 1) & buckets) |
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119 if (!cmp(a + i, b + h[j])) |
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120 break; |
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121 |
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122 a[i].h = j; /* use equivalence class for quick compare */ |
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123 if(l[j] <= t) |
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124 a[i].n = h[j]; /* point to head of match list */ |
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125 else |
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126 a[i].n = -1; /* too popular */ |
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127 } |
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128 |
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129 /* discard hash tables */ |
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130 free(h); |
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131 free(l); |
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132 return 1; |
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133 } |
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134 |
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135 static int longest_match(struct line *a, struct line *b, int *jpos, int *jlen, |
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136 int a1, int a2, int b1, int b2, int *omi, int *omj) |
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137 { |
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138 int mi = a1, mj = b1, mk = 0, mb = 0, i, j, k; |
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139 |
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140 for (i = a1; i < a2; i++) { |
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141 /* skip things before the current block */ |
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142 for (j = a[i].n; j != -1 && j < b1; j = b[j].n) |
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143 ; |
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144 |
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145 /* loop through all lines match a[i] in b */ |
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146 for (; j != -1 && j < b2; j = b[j].n) { |
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147 /* does this extend an earlier match? */ |
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148 if (i > a1 && j > b1 && jpos[j - 1] == i) |
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149 k = jlen[j - 1] + 1; |
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150 else |
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151 k = 1; |
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152 jpos[j] = i + 1; |
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153 jlen[j] = k; |
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154 |
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155 /* best match so far? */ |
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156 if (k > mk) { |
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157 mi = i; |
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158 mj = j; |
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159 mk = k; |
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160 } |
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161 } |
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162 } |
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163 |
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164 if (mk) { |
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165 mi = mi - mk + 1; |
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166 mj = mj - mk + 1; |
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167 } |
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168 |
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169 /* expand match to include neighboring popular lines */ |
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170 while (mi - mb > a1 && mj - mb > b1 && |
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171 a[mi - mb - 1].h == b[mj - mb - 1].h) |
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172 mb++; |
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173 while (mi + mk < a2 && mj + mk < b2 && |
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174 a[mi + mk].h == b[mj + mk].h) |
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175 mk++; |
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176 |
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177 *omi = mi - mb; |
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178 *omj = mj - mb; |
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179 return mk + mb; |
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180 } |
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181 |
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182 static void recurse(struct line *a, struct line *b, int *jpos, int *jlen, |
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183 int a1, int a2, int b1, int b2, struct hunklist *l) |
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184 { |
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185 int i, j, k; |
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186 |
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187 /* find the longest match in this chunk */ |
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188 k = longest_match(a, b, jpos, jlen, a1, a2, b1, b2, &i, &j); |
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189 if (!k) |
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190 return; |
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191 |
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192 /* and recurse on the remaining chunks on either side */ |
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193 recurse(a, b, jpos, jlen, a1, i, b1, j, l); |
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194 l->head->a1 = i; |
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195 l->head->a2 = i + k; |
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196 l->head->b1 = j; |
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197 l->head->b2 = j + k; |
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198 l->head++; |
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199 recurse(a, b, jpos, jlen, i + k, a2, j + k, b2, l); |
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200 } |
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201 |
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202 static PyObject *bdiff(PyObject *self, PyObject *args) |
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203 { |
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204 PyObject *sa, *sb, *result = NULL; |
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205 struct hunklist l; |
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206 struct hunk *h; |
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207 struct line *al, *bl; |
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208 char encode[12], *rb; |
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209 int an, bn, len = 0, t, la = 0, lb = 0, *jpos, *jlen; |
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210 |
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211 if (!PyArg_ParseTuple(args, "SS:bdiff", &sa, &sb)) |
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212 return NULL; |
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213 |
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214 /* allocate and fill arrays */ |
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215 an = splitlines(PyString_AsString(sa), PyString_Size(sa), &al); |
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216 bn = splitlines(PyString_AsString(sb), PyString_Size(sb), &bl); |
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217 t = equatelines(al, an, bl, bn); |
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218 jpos = calloc(bn, sizeof(int)); |
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219 jlen = calloc(bn, sizeof(int)); |
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220 l.head = l.base = malloc(sizeof(struct hunk) * ((an + bn) / 4 + 2)); |
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221 if (!al || !bl || !jpos || !jlen || !l.base || !t) |
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222 goto nomem; |
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223 |
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224 /* generate the matching block list */ |
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225 recurse(al, bl, jpos, jlen, 0, an, 0, bn, &l); |
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226 l.head->a1 = an; |
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227 l.head->b1 = bn; |
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228 l.head++; |
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229 |
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230 /* calculate length of output */ |
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231 for(h = l.base; h != l.head; h++) { |
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232 if (h->a1 != la || h->b1 != lb) |
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233 len += 12 + bl[h->b1].l - bl[lb].l; |
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234 la = h->a2; |
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235 lb = h->b2; |
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236 } |
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237 |
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238 result = PyString_FromStringAndSize(NULL, len); |
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239 if (!result) |
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240 goto nomem; |
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241 |
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242 /* build binary patch */ |
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243 rb = PyString_AsString(result); |
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244 la = lb = 0; |
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245 |
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246 for(h = l.base; h != l.head; h++) { |
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247 if (h->a1 != la || h->b1 != lb) { |
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248 len = bl[h->b1].l - bl[lb].l; |
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249 *(uint32_t *)(encode) = htonl(al[la].l - al->l); |
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250 *(uint32_t *)(encode + 4) = htonl(al[h->a1].l - al->l); |
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251 *(uint32_t *)(encode + 8) = htonl(len); |
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252 memcpy(rb, encode, 12); |
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253 memcpy(rb + 12, bl[lb].l, len); |
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254 rb += 12 + len; |
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255 } |
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256 la = h->a2; |
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257 lb = h->b2; |
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258 } |
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259 |
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260 nomem: |
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261 free(al); |
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262 free(bl); |
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263 free(jpos); |
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264 free(jlen); |
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265 free(l.base); |
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266 return result ? result : PyErr_NoMemory(); |
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267 } |
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268 |
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269 static char mdiff_doc[] = "Efficient binary diff."; |
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270 |
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271 static PyMethodDef methods[] = { |
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272 {"bdiff", bdiff, METH_VARARGS, "calculate a binary diff\n"}, |
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273 {NULL, NULL} |
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274 }; |
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275 |
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276 PyMODINIT_FUNC initbdiff(void) |
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277 { |
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278 Py_InitModule3("bdiff", methods, mdiff_doc); |
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279 } |