ARM Shanghai IoT Team (Internal) / newMiniTLS-GPL

change some parameters in the library to meet the needs of the website httpbin.org

Fork of MiniTLS-GPL by Donatien Garnier

math/mont/fp_montgomery_setup.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 /* setups the montgomery reduction */
MiniTLS 0:35aa5be3b78d 13 int fp_montgomery_setup(fp_int *a, fp_digit *rho)
MiniTLS 0:35aa5be3b78d 14 {
MiniTLS 0:35aa5be3b78d 15 fp_digit x, b;
MiniTLS 0:35aa5be3b78d 16
MiniTLS 0:35aa5be3b78d 17 /* fast inversion mod 2**k
MiniTLS 0:35aa5be3b78d 18 *
MiniTLS 0:35aa5be3b78d 19 * Based on the fact that
MiniTLS 0:35aa5be3b78d 20 *
MiniTLS 0:35aa5be3b78d 21 * XA = 1 (mod 2**n) => (X(2-XA)) A = 1 (mod 2**2n)
MiniTLS 0:35aa5be3b78d 22 * => 2*X*A - X*X*A*A = 1
MiniTLS 0:35aa5be3b78d 23 * => 2*(1) - (1) = 1
MiniTLS 0:35aa5be3b78d 24 */
MiniTLS 0:35aa5be3b78d 25 b = a->dp[0];
MiniTLS 0:35aa5be3b78d 26
MiniTLS 0:35aa5be3b78d 27 if ((b & 1) == 0) {
MiniTLS 0:35aa5be3b78d 28 return FP_VAL;
MiniTLS 0:35aa5be3b78d 29 }
MiniTLS 0:35aa5be3b78d 30
MiniTLS 0:35aa5be3b78d 31 x = (((b + 2) & 4) << 1) + b; /* here x*a==1 mod 2**4 */
MiniTLS 0:35aa5be3b78d 32 x *= 2 - b * x; /* here x*a==1 mod 2**8 */
MiniTLS 0:35aa5be3b78d 33 x *= 2 - b * x; /* here x*a==1 mod 2**16 */
MiniTLS 0:35aa5be3b78d 34 x *= 2 - b * x; /* here x*a==1 mod 2**32 */
MiniTLS 0:35aa5be3b78d 35 #ifdef FP_64BIT
MiniTLS 0:35aa5be3b78d 36 x *= 2 - b * x; /* here x*a==1 mod 2**64 */
MiniTLS 0:35aa5be3b78d 37 #endif
MiniTLS 0:35aa5be3b78d 38
MiniTLS 0:35aa5be3b78d 39 /* rho = -1/m mod b */
MiniTLS 0:35aa5be3b78d 40 *rho = (((fp_word) 1 << ((fp_word) DIGIT_BIT)) - ((fp_word)x));
MiniTLS 0:35aa5be3b78d 41
MiniTLS 0:35aa5be3b78d 42 return FP_OKAY;
MiniTLS 0:35aa5be3b78d 43 }
MiniTLS 0:35aa5be3b78d 44
MiniTLS 0:35aa5be3b78d 45
MiniTLS 0:35aa5be3b78d 46 /* $Source: /cvs/libtom/tomsfastmath/src/mont/fp_montgomery_setup.c,v $ */
MiniTLS 0:35aa5be3b78d 47 /* $Revision: 1.1 $ */
MiniTLS 0:35aa5be3b78d 48 /* $Date: 2006/12/31 21:25:53 $ */