ARM Shanghai IoT Team (Internal) / newMiniTLS-GPL

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Fork of MiniTLS-GPL by Donatien Garnier

math/bit/fp_div_2.c@0:35aa5be3b78d, 2014-06-06 (annotated)

Committer:
MiniTLS
Date:
Fri Jun 06 10:49:02 2014 +0000
Revision:
0:35aa5be3b78d
Initial commit

Who changed what in which revision?

UserRevisionLine numberNew contents of line
MiniTLS 0:35aa5be3b78d 1 /* TomsFastMath, a fast ISO C bignum library.
MiniTLS 0:35aa5be3b78d 2 *
MiniTLS 0:35aa5be3b78d 3 * This project is meant to fill in where LibTomMath
MiniTLS 0:35aa5be3b78d 4 * falls short. That is speed ;-)
MiniTLS 0:35aa5be3b78d 5 *
MiniTLS 0:35aa5be3b78d 6 * This project is public domain and free for all purposes.
MiniTLS 0:35aa5be3b78d 7 *
MiniTLS 0:35aa5be3b78d 8 * Tom St Denis, tomstdenis@gmail.com
MiniTLS 0:35aa5be3b78d 9 */
MiniTLS 0:35aa5be3b78d 10 #include <tfm.h>
MiniTLS 0:35aa5be3b78d 11
MiniTLS 0:35aa5be3b78d 12 /* b = a/2 */
MiniTLS 0:35aa5be3b78d 13 void fp_div_2(fp_int * a, fp_int * b)
MiniTLS 0:35aa5be3b78d 14 {
MiniTLS 0:35aa5be3b78d 15 int x, oldused;
MiniTLS 0:35aa5be3b78d 16
MiniTLS 0:35aa5be3b78d 17 oldused = b->used;
MiniTLS 0:35aa5be3b78d 18 b->used = a->used;
MiniTLS 0:35aa5be3b78d 19 {
MiniTLS 0:35aa5be3b78d 20 register fp_digit r, rr, *tmpa, *tmpb;
MiniTLS 0:35aa5be3b78d 21
MiniTLS 0:35aa5be3b78d 22 /* source alias */
MiniTLS 0:35aa5be3b78d 23 tmpa = a->dp + b->used - 1;
MiniTLS 0:35aa5be3b78d 24
MiniTLS 0:35aa5be3b78d 25 /* dest alias */
MiniTLS 0:35aa5be3b78d 26 tmpb = b->dp + b->used - 1;
MiniTLS 0:35aa5be3b78d 27
MiniTLS 0:35aa5be3b78d 28 /* carry */
MiniTLS 0:35aa5be3b78d 29 r = 0;
MiniTLS 0:35aa5be3b78d 30 for (x = b->used - 1; x >= 0; x--) {
MiniTLS 0:35aa5be3b78d 31 /* get the carry for the next iteration */
MiniTLS 0:35aa5be3b78d 32 rr = *tmpa & 1;
MiniTLS 0:35aa5be3b78d 33
MiniTLS 0:35aa5be3b78d 34 /* shift the current digit, add in carry and store */
MiniTLS 0:35aa5be3b78d 35 *tmpb-- = (*tmpa-- >> 1) | (r << (DIGIT_BIT - 1));
MiniTLS 0:35aa5be3b78d 36
MiniTLS 0:35aa5be3b78d 37 /* forward carry to next iteration */
MiniTLS 0:35aa5be3b78d 38 r = rr;
MiniTLS 0:35aa5be3b78d 39 }
MiniTLS 0:35aa5be3b78d 40
MiniTLS 0:35aa5be3b78d 41 /* zero excess digits */
MiniTLS 0:35aa5be3b78d 42 tmpb = b->dp + b->used;
MiniTLS 0:35aa5be3b78d 43 for (x = b->used; x < oldused; x++) {
MiniTLS 0:35aa5be3b78d 44 *tmpb++ = 0;
MiniTLS 0:35aa5be3b78d 45 }
MiniTLS 0:35aa5be3b78d 46 }
MiniTLS 0:35aa5be3b78d 47 b->sign = a->sign;
MiniTLS 0:35aa5be3b78d 48 fp_clamp (b);
MiniTLS 0:35aa5be3b78d 49 }
MiniTLS 0:35aa5be3b78d 50
MiniTLS 0:35aa5be3b78d 51 /* $Source: /cvs/libtom/tomsfastmath/src/bit/fp_div_2.c,v $ */
MiniTLS 0:35aa5be3b78d 52 /* $Revision: 1.1 $ */
MiniTLS 0:35aa5be3b78d 53 /* $Date: 2006/12/31 21:25:53 $ */