largefiles: make scheme regex a bytes regex
# skip-blame just a b prefix
Differential Revision: https://phab.mercurial-scm.org/D2338
/*
mpatch.c - efficient binary patching for Mercurial
This implements a patch algorithm that's O(m + nlog n) where m is the
size of the output and n is the number of patches.
Given a list of binary patches, it unpacks each into a hunk list,
then combines the hunk lists with a treewise recursion to form a
single hunk list. This hunk list is then applied to the original
text.
The text (or binary) fragments are copied directly from their source
Python objects into a preallocated output string to avoid the
allocation of intermediate Python objects. Working memory is about 2x
the total number of hunks.
Copyright 2005, 2006 Matt Mackall <mpm@selenic.com>
This software may be used and distributed according to the terms
of the GNU General Public License, incorporated herein by reference.
*/
#include <stdlib.h>
#include <string.h>
#include "bitmanipulation.h"
#include "compat.h"
#include "mpatch.h"
static struct mpatch_flist *lalloc(ssize_t size)
{
struct mpatch_flist *a = NULL;
if (size < 1)
size = 1;
a = (struct mpatch_flist *)malloc(sizeof(struct mpatch_flist));
if (a) {
a->base = (struct mpatch_frag *)malloc(
sizeof(struct mpatch_frag) * size);
if (a->base) {
a->head = a->tail = a->base;
return a;
}
free(a);
}
return NULL;
}
void mpatch_lfree(struct mpatch_flist *a)
{
if (a) {
free(a->base);
free(a);
}
}
static ssize_t lsize(struct mpatch_flist *a)
{
return a->tail - a->head;
}
/* move hunks in source that are less cut to dest, compensating
for changes in offset. the last hunk may be split if necessary.
*/
static int gather(struct mpatch_flist *dest, struct mpatch_flist *src, int cut,
int offset)
{
struct mpatch_frag *d = dest->tail, *s = src->head;
int postend, c, l;
while (s != src->tail) {
if (s->start + offset >= cut)
break; /* we've gone far enough */
postend = offset + s->start + s->len;
if (postend <= cut) {
/* save this hunk */
offset += s->start + s->len - s->end;
*d++ = *s++;
} else {
/* break up this hunk */
c = cut - offset;
if (s->end < c)
c = s->end;
l = cut - offset - s->start;
if (s->len < l)
l = s->len;
offset += s->start + l - c;
d->start = s->start;
d->end = c;
d->len = l;
d->data = s->data;
d++;
s->start = c;
s->len = s->len - l;
s->data = s->data + l;
break;
}
}
dest->tail = d;
src->head = s;
return offset;
}
/* like gather, but with no output list */
static int discard(struct mpatch_flist *src, int cut, int offset)
{
struct mpatch_frag *s = src->head;
int postend, c, l;
while (s != src->tail) {
if (s->start + offset >= cut)
break;
postend = offset + s->start + s->len;
if (postend <= cut) {
offset += s->start + s->len - s->end;
s++;
} else {
c = cut - offset;
if (s->end < c)
c = s->end;
l = cut - offset - s->start;
if (s->len < l)
l = s->len;
offset += s->start + l - c;
s->start = c;
s->len = s->len - l;
s->data = s->data + l;
break;
}
}
src->head = s;
return offset;
}
/* combine hunk lists a and b, while adjusting b for offset changes in a/
this deletes a and b and returns the resultant list. */
static struct mpatch_flist *combine(struct mpatch_flist *a,
struct mpatch_flist *b)
{
struct mpatch_flist *c = NULL;
struct mpatch_frag *bh, *ct;
int offset = 0, post;
if (a && b)
c = lalloc((lsize(a) + lsize(b)) * 2);
if (c) {
for (bh = b->head; bh != b->tail; bh++) {
/* save old hunks */
offset = gather(c, a, bh->start, offset);
/* discard replaced hunks */
post = discard(a, bh->end, offset);
/* insert new hunk */
ct = c->tail;
ct->start = bh->start - offset;
ct->end = bh->end - post;
ct->len = bh->len;
ct->data = bh->data;
c->tail++;
offset = post;
}
/* hold on to tail from a */
memcpy(c->tail, a->head, sizeof(struct mpatch_frag) * lsize(a));
c->tail += lsize(a);
}
mpatch_lfree(a);
mpatch_lfree(b);
return c;
}
/* decode a binary patch into a hunk list */
int mpatch_decode(const char *bin, ssize_t len, struct mpatch_flist **res)
{
struct mpatch_flist *l;
struct mpatch_frag *lt;
int pos = 0;
/* assume worst case size, we won't have many of these lists */
l = lalloc(len / 12 + 1);
if (!l)
return MPATCH_ERR_NO_MEM;
lt = l->tail;
while (pos >= 0 && pos < len) {
lt->start = getbe32(bin + pos);
lt->end = getbe32(bin + pos + 4);
lt->len = getbe32(bin + pos + 8);
lt->data = bin + pos + 12;
pos += 12 + lt->len;
if (lt->start > lt->end || lt->len < 0)
break; /* sanity check */
lt++;
}
if (pos != len) {
mpatch_lfree(l);
return MPATCH_ERR_CANNOT_BE_DECODED;
}
l->tail = lt;
*res = l;
return 0;
}
/* calculate the size of resultant text */
ssize_t mpatch_calcsize(ssize_t len, struct mpatch_flist *l)
{
ssize_t outlen = 0, last = 0;
struct mpatch_frag *f = l->head;
while (f != l->tail) {
if (f->start < last || f->end > len) {
return MPATCH_ERR_INVALID_PATCH;
}
outlen += f->start - last;
last = f->end;
outlen += f->len;
f++;
}
outlen += len - last;
return outlen;
}
int mpatch_apply(char *buf, const char *orig, ssize_t len,
struct mpatch_flist *l)
{
struct mpatch_frag *f = l->head;
int last = 0;
char *p = buf;
while (f != l->tail) {
if (f->start < last || f->end > len) {
return MPATCH_ERR_INVALID_PATCH;
}
memcpy(p, orig + last, f->start - last);
p += f->start - last;
memcpy(p, f->data, f->len);
last = f->end;
p += f->len;
f++;
}
memcpy(p, orig + last, len - last);
return 0;
}
/* recursively generate a patch of all bins between start and end */
struct mpatch_flist *
mpatch_fold(void *bins, struct mpatch_flist *(*get_next_item)(void *, ssize_t),
ssize_t start, ssize_t end)
{
ssize_t len;
if (start + 1 == end) {
/* trivial case, output a decoded list */
return get_next_item(bins, start);
}
/* divide and conquer, memory management is elsewhere */
len = (end - start) / 2;
return combine(mpatch_fold(bins, get_next_item, start, start + len),
mpatch_fold(bins, get_next_item, start + len, end));
}