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/*
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mpatch.c - efficient binary patching for Mercurial
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This implements a patch algorithm that's O(m + nlog n) where m is the
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size of the output and n is the number of patches.
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Given a list of binary patches, it unpacks each into a hunk list,
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then combines the hunk lists with a treewise recursion to form a
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single hunk list. This hunk list is then applied to the original
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text.
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The text (or binary) fragments are copied directly from their source
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Python objects into a preallocated output string to avoid the
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allocation of intermediate Python objects. Working memory is about 2x
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the total number of hunks.
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Copyright 2005 Matt Mackall <mpm@selenic.com>
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This software may be used and distributed according to the terms
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of the GNU General Public License, incorporated herein by reference.
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*/
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#include <Python.h>
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#include <stdlib.h>
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#include <string.h>
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#ifdef _WIN32
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typedef unsigned long uint32_t;
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static uint32_t ntohl(uint32_t x)
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{
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return ((x & 0x000000ffUL) << 24) |
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((x & 0x0000ff00UL) << 8) |
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((x & 0x00ff0000UL) >> 8) |
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((x & 0xff000000UL) >> 24);
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}
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#else
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#include <netinet/in.h>
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#include <sys/types.h>
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#include <stdint.h>
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#endif
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static char mpatch_doc[] = "Efficient binary patching.";
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struct frag {
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int start, end, len;
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char *data;
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};
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struct flist {
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struct frag *base, *head, *tail;
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};
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static struct flist *lalloc(int size)
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{
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struct flist *a = NULL;
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a = malloc(sizeof(struct flist));
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if (a) {
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a->base = malloc(sizeof(struct frag) * size);
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if (!a->base) {
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free(a);
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a = NULL;
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} else
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a->head = a->tail = a->base;
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}
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return a;
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}
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static void lfree(struct flist *a)
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{
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if (a) {
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free(a->base);
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free(a);
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}
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}
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static int lsize(struct flist *a)
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{
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return a->tail - a->head;
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}
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/* move hunks in source that are less cut to dest, compensating
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for changes in offset. the last hunk may be split if necessary.
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*/
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static int gather(struct flist *dest, struct flist *src, int cut, int offset)
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{
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struct frag *d = dest->tail, *s = src->head;
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int postend, c, l;
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while (s != src->tail) {
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if (s->start + offset >= cut)
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break; /* we've gone far enough */
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postend = offset + s->start + s->len;
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if (postend <= cut) {
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/* save this hunk */
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offset += s->start + s->len - s->end;
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*d++ = *s++;
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}
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else {
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/* break up this hunk */
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c = cut - offset;
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if (s->end < c)
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c = s->end;
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l = cut - offset - s->start;
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if (s->len < l)
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l = s->len;
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offset += s->start + l - c;
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d->start = s->start;
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d->end = c;
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d->len = l;
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d->data = s->data;
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d++;
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s->start = c;
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s->len = s->len - l;
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s->data = s->data + l;
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break;
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}
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}
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dest->tail = d;
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src->head = s;
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return offset;
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}
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/* like gather, but with no output list */
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static int discard(struct flist *src, int cut, int offset)
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{
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struct frag *s = src->head;
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int postend, c, l;
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while (s != src->tail) {
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if (s->start + offset >= cut)
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break;
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postend = offset + s->start + s->len;
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if (postend <= cut) {
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offset += s->start + s->len - s->end;
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s++;
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}
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else {
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c = cut - offset;
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if (s->end < c)
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c = s->end;
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l = cut - offset - s->start;
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if (s->len < l)
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l = s->len;
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offset += s->start + l - c;
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s->start = c;
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s->len = s->len - l;
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s->data = s->data + l;
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break;
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}
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}
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src->head = s;
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return offset;
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}
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/* combine hunk lists a and b, while adjusting b for offset changes in a/
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this deletes a and b and returns the resultant list. */
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static struct flist *combine(struct flist *a, struct flist *b)
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{
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struct flist *c = NULL;
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struct frag *bh, *ct;
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int offset = 0, post;
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if (a && b)
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c = lalloc((lsize(a) + lsize(b)) * 2);
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if (c) {
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for (bh = b->head; bh != b->tail; bh++) {
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/* save old hunks */
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offset = gather(c, a, bh->start, offset);
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/* discard replaced hunks */
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post = discard(a, bh->end, offset);
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/* insert new hunk */
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ct = c->tail;
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ct->start = bh->start - offset;
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ct->end = bh->end - post;
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ct->len = bh->len;
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ct->data = bh->data;
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c->tail++;
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offset = post;
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}
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/* hold on to tail from a */
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memcpy(c->tail, a->head, sizeof(struct frag) * lsize(a));
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c->tail += lsize(a);
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}
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lfree(a);
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lfree(b);
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return c;
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}
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/* decode a binary patch into a hunk list */
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static struct flist *decode(char *bin, int len)
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{
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struct flist *l;
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struct frag *lt;
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char *end = bin + len;
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char decode[12]; /* for dealing with alignment issues */
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/* assume worst case size, we won't have many of these lists */
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l = lalloc(len / 12);
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lt = l->tail;
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while (bin < end) {
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memcpy(decode, bin, 12);
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lt->start = ntohl(*(uint32_t *)decode);
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lt->end = ntohl(*(uint32_t *)(decode + 4));
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lt->len = ntohl(*(uint32_t *)(decode + 8));
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lt->data = bin + 12;
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bin += 12 + lt->len;
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lt++;
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}
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l->tail = lt;
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return l;
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}
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/* calculate the size of resultant text */
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static int calcsize(int len, struct flist *l)
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{
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int outlen = 0, last = 0;
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struct frag *f = l->head;
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while (f != l->tail) {
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outlen += f->start - last;
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last = f->end;
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outlen += f->len;
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f++;
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}
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outlen += len - last;
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return outlen;
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}
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static void apply(char *buf, char *orig, int len, struct flist *l)
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{
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struct frag *f = l->head;
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int last = 0;
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char *p = buf;
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while (f != l->tail) {
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memcpy(p, orig + last, f->start - last);
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p += f->start - last;
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memcpy(p, f->data, f->len);
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last = f->end;
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p += f->len;
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f++;
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}
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memcpy(p, orig + last, len - last);
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}
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/* recursively generate a patch of all bins between start and end */
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static struct flist *fold(PyObject *bins, int start, int end)
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{
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int len;
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if (start + 1 == end) {
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/* trivial case, output a decoded list */
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PyObject *tmp = PyList_GetItem(bins, start);
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if (!tmp)
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return NULL;
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return decode(PyString_AsString(tmp), PyString_Size(tmp));
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}
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/* divide and conquer, memory management is elsewhere */
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len = (end - start) / 2;
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return combine(fold(bins, start, start + len),
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fold(bins, start + len, end));
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}
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static PyObject *
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patches(PyObject *self, PyObject *args)
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{
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PyObject *text, *bins, *result;
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struct flist *patch;
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char *in, *out;
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int len, outlen;
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if (!PyArg_ParseTuple(args, "SO:mpatch", &text, &bins))
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return NULL;
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len = PyList_Size(bins);
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if (!len) {
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/* nothing to do */
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Py_INCREF(text);
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return text;
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}
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patch = fold(bins, 0, len);
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if (!patch)
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return PyErr_NoMemory();
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outlen = calcsize(PyString_Size(text), patch);
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result = PyString_FromStringAndSize(NULL, outlen);
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if (result) {
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in = PyString_AsString(text);
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out = PyString_AsString(result);
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apply(out, in, PyString_Size(text), patch);
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}
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lfree(patch);
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return result;
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}
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static PyMethodDef methods[] = {
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{"patches", patches, METH_VARARGS, "apply a series of patches\n"},
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{NULL, NULL}
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};
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PyMODINIT_FUNC
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initmpatch(void)
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{
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Py_InitModule3("mpatch", methods, mpatch_doc);
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}
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