| #include <tommath.h> |

| #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 $ */ |