// SPDX-License-Identifiler: WTFPL
#include <stdio.h>
#include <string.h>
#include <stdint.h>
#include "bzcomp.h"

int32_t bz_uncompress(uint8_t *dst, uint8_t *src, int32_t dlen, int32_t slen)
{
	uint32_t i, c, n, spos, dpos, xpos, xlen;

	if (dst == NULL) dlen = 1U << 31;

	for (spos = dpos = 0;
	     spos < slen && dpos < dlen; spos += n, dpos += xlen) {
		c = src[spos] & 0xf0;
		if (c == 0x00 || c == 0x10) {
			xlen = (src[spos] & 0x1f) + 1;
			n = xlen + 1;
			if (slen - spos < n) goto error;
			if (dst != NULL) {
				if (dlen - dpos < xlen) goto error;
				memcpy(dst + dpos, src + spos + 1, xlen);
			}
		} else {
			n = (c == 0xf0) ? 3 : 2;
			if (slen - spos < n) goto error;
			if (c == 0xf0) {
				xlen = (((src[spos] & 0x0f) << 4) |
					((src[spos + 1] & 0xf0) >> 4)) + 1;
				xpos = ((src[spos + 1] & 0x0f) << 8) |
					src[spos + 2];
			} else {
				xlen = ((src[spos] & 0xf0) >> 4) + 1;
				xpos = ((src[spos] & 0x0f) << 8) |
					src[spos + 1];
			}
			if (!xpos || xpos > dpos)
				goto error;
			if (dst != NULL) {
				if (dlen - dpos < xlen) goto error;
				/* do not use memcpy() and memmove() */
				for (i = 0; i < xlen; i++)
					dst[dpos + i] = dst[dpos - xpos + i];
			}
		}
	}

	return (int32_t)dpos;

error:
	return -1;
}