xref: /freebsd/contrib/bearssl/src/int/i15_rshift.c (revision 2aaf9152a852aba9eb2036b95f4948ee77988826)
1*0957b409SSimon J. Gerraty /*
2*0957b409SSimon J. Gerraty  * Copyright (c) 2017 Thomas Pornin <pornin@bolet.org>
3*0957b409SSimon J. Gerraty  *
4*0957b409SSimon J. Gerraty  * Permission is hereby granted, free of charge, to any person obtaining
5*0957b409SSimon J. Gerraty  * a copy of this software and associated documentation files (the
6*0957b409SSimon J. Gerraty  * "Software"), to deal in the Software without restriction, including
7*0957b409SSimon J. Gerraty  * without limitation the rights to use, copy, modify, merge, publish,
8*0957b409SSimon J. Gerraty  * distribute, sublicense, and/or sell copies of the Software, and to
9*0957b409SSimon J. Gerraty  * permit persons to whom the Software is furnished to do so, subject to
10*0957b409SSimon J. Gerraty  * the following conditions:
11*0957b409SSimon J. Gerraty  *
12*0957b409SSimon J. Gerraty  * The above copyright notice and this permission notice shall be
13*0957b409SSimon J. Gerraty  * included in all copies or substantial portions of the Software.
14*0957b409SSimon J. Gerraty  *
15*0957b409SSimon J. Gerraty  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
16*0957b409SSimon J. Gerraty  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
17*0957b409SSimon J. Gerraty  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
18*0957b409SSimon J. Gerraty  * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
19*0957b409SSimon J. Gerraty  * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
20*0957b409SSimon J. Gerraty  * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
21*0957b409SSimon J. Gerraty  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
22*0957b409SSimon J. Gerraty  * SOFTWARE.
23*0957b409SSimon J. Gerraty  */
24*0957b409SSimon J. Gerraty 
25*0957b409SSimon J. Gerraty #include "inner.h"
26*0957b409SSimon J. Gerraty 
27*0957b409SSimon J. Gerraty /* see inner.h */
28*0957b409SSimon J. Gerraty void
br_i15_rshift(uint16_t * x,int count)29*0957b409SSimon J. Gerraty br_i15_rshift(uint16_t *x, int count)
30*0957b409SSimon J. Gerraty {
31*0957b409SSimon J. Gerraty 	size_t u, len;
32*0957b409SSimon J. Gerraty 	unsigned r;
33*0957b409SSimon J. Gerraty 
34*0957b409SSimon J. Gerraty 	len = (x[0] + 15) >> 4;
35*0957b409SSimon J. Gerraty 	if (len == 0) {
36*0957b409SSimon J. Gerraty 		return;
37*0957b409SSimon J. Gerraty 	}
38*0957b409SSimon J. Gerraty 	r = x[1] >> count;
39*0957b409SSimon J. Gerraty 	for (u = 2; u <= len; u ++) {
40*0957b409SSimon J. Gerraty 		unsigned w;
41*0957b409SSimon J. Gerraty 
42*0957b409SSimon J. Gerraty 		w = x[u];
43*0957b409SSimon J. Gerraty 		x[u - 1] = ((w << (15 - count)) | r) & 0x7FFF;
44*0957b409SSimon J. Gerraty 		r = w >> count;
45*0957b409SSimon J. Gerraty 	}
46*0957b409SSimon J. Gerraty 	x[len] = r;
47*0957b409SSimon J. Gerraty }
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