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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, 2006 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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#define PY_SSIZE_T_CLEAN
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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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#include "util.h"
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#include "bitmanipulation.h"
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#include "compat.h"
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static char mpatch_doc[] = "Efficient binary patching.";
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static PyObject *mpatch_Error;
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struct mpatch_frag {
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int start, end, len;
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const char *data;
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};
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struct mpatch_flist {
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struct mpatch_frag *base, *head, *tail;
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};
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struct mpatch_flist *lalloc(ssize_t size)
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{
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struct mpatch_flist *a = NULL;
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if (size < 1)
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size = 1;
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a = (struct mpatch_flist *)malloc(sizeof(struct mpatch_flist));
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if (a) {
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a->base = (struct mpatch_frag *)malloc(sizeof(struct mpatch_frag) * size);
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if (a->base) {
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a->head = a->tail = a->base;
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return a;
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}
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free(a);
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a = NULL;
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}
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if (!PyErr_Occurred())
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PyErr_NoMemory();
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return NULL;
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}
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void mpatch_lfree(struct mpatch_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 ssize_t lsize(struct mpatch_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 mpatch_flist *dest, struct mpatch_flist *src, int cut,
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int offset)
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{
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struct mpatch_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 mpatch_flist *src, int cut, int offset)
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{
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struct mpatch_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 mpatch_flist *combine(struct mpatch_flist *a,
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struct mpatch_flist *b)
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{
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struct mpatch_flist *c = NULL;
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struct mpatch_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 mpatch_frag) * lsize(a));
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c->tail += lsize(a);
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}
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mpatch_lfree(a);
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mpatch_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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struct mpatch_flist *mpatch_decode(const char *bin, ssize_t len)
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{
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struct mpatch_flist *l;
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struct mpatch_frag *lt;
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int pos = 0;
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/* assume worst case size, we won't have many of these lists */
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l = lalloc(len / 12 + 1);
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if (!l)
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return NULL;
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lt = l->tail;
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while (pos >= 0 && pos < len) {
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lt->start = getbe32(bin + pos);
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lt->end = getbe32(bin + pos + 4);
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lt->len = getbe32(bin + pos + 8);
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lt->data = bin + pos + 12;
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pos += 12 + lt->len;
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if (lt->start > lt->end || lt->len < 0)
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break; /* sanity check */
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lt++;
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}
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if (pos != len) {
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if (!PyErr_Occurred())
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PyErr_SetString(mpatch_Error, "patch cannot be decoded");
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mpatch_lfree(l);
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return NULL;
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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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ssize_t mpatch_calcsize(ssize_t len, struct mpatch_flist *l)
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{
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ssize_t outlen = 0, last = 0;
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struct mpatch_frag *f = l->head;
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while (f != l->tail) {
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if (f->start < last || f->end > len) {
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if (!PyErr_Occurred())
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PyErr_SetString(mpatch_Error,
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"invalid patch");
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return -1;
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}
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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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int mpatch_apply(char *buf, const char *orig, ssize_t len,
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struct mpatch_flist *l)
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{
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struct mpatch_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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if (f->start < last || f->end > len) {
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if (!PyErr_Occurred())
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PyErr_SetString(mpatch_Error,
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"invalid patch");
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return 0;
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}
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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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return 1;
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}
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/* recursively generate a patch of all bins between start and end */
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struct mpatch_flist *mpatch_fold(PyObject *bins, ssize_t start,
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ssize_t end)
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{
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ssize_t len, blen;
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const char *buffer;
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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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if (PyObject_AsCharBuffer(tmp, &buffer, &blen))
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return NULL;
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return mpatch_decode(buffer, blen);
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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(mpatch_fold(bins, start, start + len),
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mpatch_fold(bins, start + len, end));
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}
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