Mercurial > dropbear
view libtommath/bn_mp_reduce_2k.c @ 374:87ae4565679d channel-fix
merge of 'a94c5265558121fe936519b5d9a5eb27f95e9d9d'
and 'd348546b80847bc0d42a7b5208bb31a54f1fdfaf'
author | Matt Johnston <matt@ucc.asn.au> |
---|---|
date | Tue, 05 Dec 2006 13:28:44 +0000 (2006-12-05) |
parents | eed26cff980b |
children | 5ff8218bcee9 |
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#include <tommath.h> #ifdef BN_MP_REDUCE_2K_C /* LibTomMath, multiple-precision integer library -- Tom St Denis * * LibTomMath is a library that provides multiple-precision * integer arithmetic as well as number theoretic functionality. * * The library was designed directly after the MPI library by * Michael Fromberger but has been written from scratch with * additional optimizations in place. * * The library is free for all purposes without any express * guarantee it works. * * Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org */ /* reduces a modulo n where n is of the form 2**p - d */ int mp_reduce_2k(mp_int *a, mp_int *n, mp_digit d) { mp_int q; int p, res; if ((res = mp_init(&q)) != MP_OKAY) { return res; } p = mp_count_bits(n); top: /* q = a/2**p, a = a mod 2**p */ if ((res = mp_div_2d(a, p, &q, a)) != MP_OKAY) { goto ERR; } if (d != 1) { /* q = q * d */ if ((res = mp_mul_d(&q, d, &q)) != MP_OKAY) { goto ERR; } } /* a = a + q */ if ((res = s_mp_add(a, &q, a)) != MP_OKAY) { goto ERR; } if (mp_cmp_mag(a, n) != MP_LT) { s_mp_sub(a, n, a); goto top; } ERR: mp_clear(&q); return res; } #endif