blob: 53b435fa9ecd1c54fef889dc994cb8bb0b61d916 [file] [log] [blame]
 #include #ifdef BN_MP_REDUCE_2K_L_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@gmail.com, http://math.libtomcrypt.com */ /* reduces a modulo n where n is of the form 2**p - d This differs from reduce_2k since "d" can be larger than a single digit. */ int mp_reduce_2k_l(mp_int *a, mp_int *n, mp_int *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; } /* q = q * d */ if ((res = mp_mul(&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 /* \$Source: /cvs/libtom/libtommath/bn_mp_reduce_2k_l.c,v \$ */ /* \$Revision: 1.3 \$ */ /* \$Date: 2006/03/31 14:18:44 \$ */