i31_decode.c

/*
 * Copyright (c) 2016 Thomas Pornin <[email protected]>
 *
 * Permission is hereby granted, free of charge, to any person obtaining 
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice shall be 
 * included in all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND 
 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#include "inner.h"

/* see inner.h */
void
br_i31_decode(uint32_t *x, const void *src, size_t len)
{
	const unsigned char *buf;
	size_t u, v;
	uint32_t acc;
	int acc_len;

	buf = src;
	u = len;
	v = 1;
	acc = 0;
	acc_len = 0;
	while (u -- > 0) {
		uint32_t b;

		b = buf[u];
		acc |= (b << acc_len);
		acc_len += 8;
		if (acc_len >= 31) {
			x[v ++] = acc & (uint32_t)0x7FFFFFFF;
			acc_len -= 31;
			acc = b >> (8 - acc_len);
		}
	}
	if (acc_len != 0) {
		x[v ++] = acc;
	}
	x[0] = br_i31_bit_length(x + 1, v - 1);
}