i31_encode.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_encode(void *dst, size_t len, const uint32_t *x)
{
	unsigned char *buf;
	size_t k, xlen;
	uint32_t acc;
	int acc_len;

	xlen = (x[0] + 31) >> 5;
	if (xlen == 0) {
		memset(dst, 0, len);
		return;
	}
	buf = (unsigned char *)dst + len;
	k = 1;
	acc = 0;
	acc_len = 0;
	while (len != 0) {
		uint32_t w;

		w = (k <= xlen) ? x[k] : 0;
		k ++;
		if (acc_len == 0) {
			acc = w;
			acc_len = 31;
		} else {
			uint32_t z;

			z = acc | (w << acc_len);
			acc_len --;
			acc = w >> (31 - acc_len);
			if (len >= 4) {
				buf -= 4;
				len -= 4;
				br_enc32be(buf, z);
			} else {
				switch (len) {
				case 3:
					buf[-3] = (unsigned char)(z >> 16);
					/* fall through */
				case 2:
					buf[-2] = (unsigned char)(z >> 8);
					/* fall through */
				case 1:
					buf[-1] = (unsigned char)z;
					break;
				}
				return;
			}
		}
	}
}