/*

 * 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;

#define PARSE_CP_PARAM(bit, var, shift) do { \

			if (cmd & (bit)) { \

				if (data >= top) \

					goto bad_length; \

				var |= ((unsigned) *data++ << (shift)); \

			} } while (0)

			PARSE_CP_PARAM(0x01, cp_off, 0);

			PARSE_CP_PARAM(0x02, cp_off, 8);

			PARSE_CP_PARAM(0x04, cp_off, 16);

			PARSE_CP_PARAM(0x08, cp_off, 24);

			PARSE_CP_PARAM(0x10, cp_size, 0);

			PARSE_CP_PARAM(0x20, cp_size, 8);

			PARSE_CP_PARAM(0x40, cp_size, 16);

#undef PARSE_CP_PARAM

			if (cp_size == 0) cp_size = 0x10000;

			if (unsigned_add_overflows(cp_off, cp_size) ||

			    cp_off + cp_size > src_size ||

			    cp_size > size)

				goto bad_length;

			memcpy(out, (char *) src_buf + cp_off, cp_size);

			out += cp_size;

			size -= cp_size;

		} else if (cmd) {

			if (cmd > size || cmd > top - data)

				goto bad_length;

			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) {

		bad_length:

		error("delta replay has gone wild");

		bad:

		free(dst_buf);

		return NULL;

	}

	*dst_size = out - dst_buf;

	return dst_buf;

}