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72
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1 /*
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2 mpatch.c - efficient binary patching for Mercurial
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3
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4 This implements a patch algorithm that's O(m + nlog n) where m is the
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5 size of the output and n is the number of patches.
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6
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7 Given a list of binary patches, it unpacks each into a hunk list,
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8 then combines the hunk lists with a treewise recursion to form a
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9 single hunk list. This hunk list is then applied to the original
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10 text.
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11
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12 The text (or binary) fragments are copied directly from their source
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13 Python objects into a preallocated output string to avoid the
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14 allocation of intermediate Python objects. Working memory is about 2x
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15 the total number of hunks.
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16
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17 Copyright 2005 Matt Mackall <mpm@selenic.com>
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18
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19 This software may be used and distributed according to the terms
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20 of the GNU General Public License, incorporated herein by reference.
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21 */
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22
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23 #include <Python.h>
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24 #include <stdlib.h>
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25 #include <string.h>
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26 #include <netinet/in.h>
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27 #include <sys/types.h>
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28
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29 static char mpatch_doc[] = "Efficient binary patching.";
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30
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31 struct frag {
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32 int start, end, len;
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33 char *data;
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34 };
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35
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36 struct flist {
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37 struct frag *base, *head, *tail;
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38 };
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39
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40 static struct flist *lalloc(int size)
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41 {
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42 struct flist *a;
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43
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44 a = malloc(sizeof(struct flist));
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45 a->head = a->tail = a->base = malloc(sizeof(struct frag) * size);
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46 return a;
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47 }
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48
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49 static void lfree(struct flist *a)
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50 {
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51 free(a->base);
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52 free(a);
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53 }
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54
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55 static int lsize(struct flist *a)
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56 {
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57 return a->tail - a->head;
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58 }
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59
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60 /* move hunks in source that are less cut to dest, compensating
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61 for changes in offset. the last hunk may be split if necessary.
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62 */
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63 static int gather(struct flist *dest, struct flist *src, int cut, int offset)
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64 {
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65 struct frag *d = dest->tail, *s = src->head;
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66 int postend, c, l;
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67
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68 while (s != src->tail) {
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69 if (s->start + offset >= cut)
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70 goto exit; /* we've gone far enough */
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71
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72 postend = offset + s->start + s->len;
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73 if (postend <= cut) {
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74 /* save this hunk */
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75 offset += s->start + s->len - s->end;
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76 *d++ = *s++;
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77 }
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78 else {
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79 /* break up this hunk */
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80 c = cut - offset;
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81 if (s->end < c)
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82 c = s->end;
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83 l = cut - offset - s->start;
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84 if (s->len < l)
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85 l = s->len;
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86
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87 offset += s->start + l - c;
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88
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89 d->start = s->start;
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90 d->end = c;
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91 d->len = l;
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92 d->data = s->data;
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93 d++;
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94 s->start = c;
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95 s->len = s->len - l;
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96 s->data = s->data + l;
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97
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98 goto exit;
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99 }
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100 }
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101
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102 exit:
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103 dest->tail = d;
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104 src->head = s;
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105 return offset;
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106 }
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107
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108 /* like gather, but with no output list */
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109 static int discard(struct flist *src, int cut, int offset)
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110 {
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111 struct frag *s = src->head;
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112 int postend, c, l;
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113
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114 while (s != src->tail) {
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115 if (s->start + offset >= cut)
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116 goto exit;
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117
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118 postend = offset + s->start + s->len;
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119 if (postend <= cut) {
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120 offset += s->start + s->len - s->end;
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121 s++;
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122 }
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123 else {
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124 c = cut - offset;
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125 if (s->end < c)
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126 c = s->end;
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127 l = cut - offset - s->start;
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128 if (s->len < l)
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129 l = s->len;
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130
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131 offset += s->start + l - c;
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132 s->start = c;
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133 s->len = s->len - l;
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134 s->data = s->data + l;
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135
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136 goto exit;
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137 }
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138 }
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139
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140 exit:
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141 src->head = s;
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142 return offset;
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143 }
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144
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145 /* combine hunk lists a and b, while adjusting b for offset changes in a/
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146 this deletes a and b and returns the resultant list. */
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147 static struct flist *combine(struct flist *a, struct flist *b)
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148 {
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149 struct flist *c;
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150 struct frag *bh = b->head, *ct;
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151 int offset = 0, post;
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152
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153 c = lalloc((lsize(a) + lsize(b)) * 2);
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154
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155 while (bh != b->tail) {
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156 /* save old hunks */
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157 offset = gather(c, a, bh->start, offset);
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158
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159 /* discard replaced hunks */
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160 post = discard(a, bh->end, offset);
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161
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162 /* insert new hunk */
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163 ct = c->tail;
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164 ct->start = bh->start - offset;
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165 ct->end = bh->end - post;
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166 ct->len = bh->len;
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167 ct->data = bh->data;
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168 c->tail++;
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169 bh++;
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170 offset = post;
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171 }
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172
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173 /* hold on to tail from a */
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174 memcpy(c->tail, a->head, sizeof(struct frag) * lsize(a));
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175 c->tail += lsize(a);
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176 lfree(a);
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177 lfree(b);
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178 return c;
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179 }
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180
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181 /* decode a binary patch into a hunk list */
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182 static struct flist *decode(char *bin, int len)
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183 {
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184 struct flist *l;
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185 struct frag *lt;
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186 char *end = bin + len;
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187
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188 /* assume worst case size, we won't have many of these lists */
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189 l = lalloc(len / 12);
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190 lt = l->tail;
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191
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192 while (bin < end) {
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193 lt->start = ntohl(*(uint32_t *)bin);
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194 lt->end = ntohl(*(uint32_t *)(bin + 4));
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195 lt->len = ntohl(*(uint32_t *)(bin + 8));
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196 lt->data = bin + 12;
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197 bin += 12 + lt->len;
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198 lt++;
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199 }
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200
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201 l->tail = lt;
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202 return l;
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203 }
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204
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205 /* calculate the size of resultant text */
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206 static int calcsize(int len, struct flist *l)
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207 {
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208 int outlen = 0, last = 0;
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209 struct frag *f = l->head;
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210
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211 while (f != l->tail) {
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212 outlen += f->start - last;
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213 last = f->end;
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214 outlen += f->len;
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215 f++;
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216 }
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217
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218 outlen += len - last;
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219 return outlen;
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220 }
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221
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222 static void apply(char *buf, char *orig, int len, struct flist *l)
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223 {
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224 struct frag *f = l->head;
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225 int last = 0;
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226 char *p = buf;
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227
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228 while (f != l->tail) {
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229 memcpy(p, orig + last, f->start - last);
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230 p += f->start - last;
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231 memcpy(p, f->data, f->len);
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232 last = f->end;
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233 p += f->len;
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234 f++;
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235 }
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236 memcpy(p, orig + last, len - last);
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237 }
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238
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239 /* recursively generate a patch of all bins between start and end */
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240 static struct flist *fold(PyObject *bins, int start, int end)
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241 {
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242 int len;
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243
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244 if (start + 1 == end) {
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245 /* trivial case, output a decoded list */
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246 PyObject *tmp = PyList_GetItem(bins, start);
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247 return decode(PyString_AsString(tmp), PyString_Size(tmp));
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248 }
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249
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250 /* divide and conquer, memory management is elsewhere */
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251 len = (end - start) / 2;
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252 return combine(fold(bins, start, start + len),
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253 fold(bins, start + len, end));
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254 }
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255
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256 static PyObject *
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257 patches(PyObject *self, PyObject *args)
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258 {
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259 PyObject *text, *bins, *result;
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260 struct flist *patch;
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261 char *in, *out;
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262 int len, outlen;
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263
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264 if (!PyArg_ParseTuple(args, "OO:mpatch", &text, &bins))
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265 return NULL;
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266
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267 len = PyList_Size(bins);
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268 if (!len) {
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269 /* nothing to do */
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270 Py_INCREF(text);
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271 return text;
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272 }
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273
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274 patch = fold(bins, 0, len);
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275 outlen = calcsize(PyString_Size(text), patch);
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276 result = PyString_FromStringAndSize(NULL, outlen);
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277 in = PyString_AsString(text);
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278 out = PyString_AsString(result);
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279 apply(out, in, PyString_Size(text), patch);
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280 lfree(patch);
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281
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282 return result;
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283 }
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284
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285 static PyMethodDef methods[] = {
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286 {"patches", patches, METH_VARARGS, "apply a series of patches\n"},
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287 {NULL, NULL}
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288 };
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289
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290 PyMODINIT_FUNC
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291 initmpatch(void)
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292 {
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293 Py_InitModule3("mpatch", methods, mpatch_doc);
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294 }
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295
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