root/patch-delta.c

DEFINITIONS

1. patch_delta

/*
 * patch-delta.c:
 * recreate a buffer from a source and the delta produced by diff-delta.c
 *
 * (C) 2005 Nicolas Pitre <nico@fluxnic.net>
 *
 * This code is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */

#include "git-compat-util.h"
#include "delta.h"

void *patch_delta(const void *src_buf, unsigned long src_size,
                  const void *delta_buf, unsigned long delta_size,
                  unsigned long *dst_size)
{
        const unsigned char *data, *top;
        unsigned char *dst_buf, *out, cmd;
        unsigned long size;

        if (delta_size < DELTA_SIZE_MIN)
                return NULL;

        data = delta_buf;
        top = (const unsigned char *) delta_buf + delta_size;

        /* make sure the orig file size matches what we expect */
        size = get_delta_hdr_size(&data, top);
        if (size != src_size)
                return NULL;

        /* now the result size */
        size = get_delta_hdr_size(&data, top);
        dst_buf = xmallocz(size);

        out = dst_buf;
        while (data < top) {
                cmd = *data++;
                if (cmd & 0x80) {
                        unsigned long cp_off = 0, cp_size = 0;
                        if (cmd & 0x01) cp_off = *data++;
                        if (cmd & 0x02) cp_off |= (*data++ << 8);
                        if (cmd & 0x04) cp_off |= (*data++ << 16);
                        if (cmd & 0x08) cp_off |= ((unsigned) *data++ << 24);
                        if (cmd & 0x10) cp_size = *data++;
                        if (cmd & 0x20) cp_size |= (*data++ << 8);
                        if (cmd & 0x40) cp_size |= (*data++ << 16);
                        if (cp_size == 0) cp_size = 0x10000;
                        if (unsigned_add_overflows(cp_off, cp_size) ||
                            cp_off + cp_size > src_size ||
                            cp_size > size)
                                break;
                        memcpy(out, (char *) src_buf + cp_off, cp_size);
                        out += cp_size;
                        size -= cp_size;
                } else if (cmd) {
                        if (cmd > size)
                                break;
                        memcpy(out, data, cmd);
                        out += cmd;
                        data += cmd;
                        size -= cmd;
                } else {
                        /*
                         * cmd == 0 is reserved for future encoding
                         * extensions. In the mean time we must fail when
                         * encountering them (might be data corruption).
                         */
                        error("unexpected delta opcode 0");
                        goto bad;
                }
        }

        /* sanity check */
        if (data != top || size != 0) {
                error("delta replay has gone wild");
                bad:
                free(dst_buf);
                return NULL;
        }

        *dst_size = out - dst_buf;
        return dst_buf;
}