diff options
Diffstat (limited to 'libtommath/bn_s_mp_sub.c')
| -rw-r--r-- | libtommath/bn_s_mp_sub.c | 122 |
1 files changed, 52 insertions, 70 deletions
diff --git a/libtommath/bn_s_mp_sub.c b/libtommath/bn_s_mp_sub.c index 8091f4a..5672dab 100644 --- a/libtommath/bn_s_mp_sub.c +++ b/libtommath/bn_s_mp_sub.c @@ -1,89 +1,71 @@ -#include <tommath_private.h> +#include "tommath_private.h" #ifdef BN_S_MP_SUB_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, tstdenis82@gmail.com, http://libtom.org - */ +/* LibTomMath, multiple-precision integer library -- Tom St Denis */ +/* SPDX-License-Identifier: Unlicense */ /* low level subtraction (assumes |a| > |b|), HAC pp.595 Algorithm 14.9 */ -int -s_mp_sub (mp_int * a, mp_int * b, mp_int * c) +mp_err s_mp_sub(const mp_int *a, const mp_int *b, mp_int *c) { - int olduse, res, min, max; + int olduse, min, max; + mp_err err; - /* find sizes */ - min = b->used; - max = a->used; + /* find sizes */ + min = b->used; + max = a->used; - /* init result */ - if (c->alloc < max) { - if ((res = mp_grow (c, max)) != MP_OKAY) { - return res; - } - } - olduse = c->used; - c->used = max; + /* init result */ + if (c->alloc < max) { + if ((err = mp_grow(c, max)) != MP_OKAY) { + return err; + } + } + olduse = c->used; + c->used = max; - { - mp_digit u, *tmpa, *tmpb, *tmpc; - int i; + { + mp_digit u, *tmpa, *tmpb, *tmpc; + int i; - /* alias for digit pointers */ - tmpa = a->dp; - tmpb = b->dp; - tmpc = c->dp; + /* alias for digit pointers */ + tmpa = a->dp; + tmpb = b->dp; + tmpc = c->dp; - /* set carry to zero */ - u = 0; - for (i = 0; i < min; i++) { - /* T[i] = A[i] - B[i] - U */ - *tmpc = (*tmpa++ - *tmpb++) - u; + /* set carry to zero */ + u = 0; + for (i = 0; i < min; i++) { + /* T[i] = A[i] - B[i] - U */ + *tmpc = (*tmpa++ - *tmpb++) - u; - /* U = carry bit of T[i] - * Note this saves performing an AND operation since - * if a carry does occur it will propagate all the way to the - * MSB. As a result a single shift is enough to get the carry - */ - u = *tmpc >> ((mp_digit)((CHAR_BIT * sizeof(mp_digit)) - 1)); + /* U = carry bit of T[i] + * Note this saves performing an AND operation since + * if a carry does occur it will propagate all the way to the + * MSB. As a result a single shift is enough to get the carry + */ + u = *tmpc >> (MP_SIZEOF_BITS(mp_digit) - 1u); - /* Clear carry from T[i] */ - *tmpc++ &= MP_MASK; - } + /* Clear carry from T[i] */ + *tmpc++ &= MP_MASK; + } - /* now copy higher words if any, e.g. if A has more digits than B */ - for (; i < max; i++) { - /* T[i] = A[i] - U */ - *tmpc = *tmpa++ - u; + /* now copy higher words if any, e.g. if A has more digits than B */ + for (; i < max; i++) { + /* T[i] = A[i] - U */ + *tmpc = *tmpa++ - u; - /* U = carry bit of T[i] */ - u = *tmpc >> ((mp_digit)((CHAR_BIT * sizeof(mp_digit)) - 1)); + /* U = carry bit of T[i] */ + u = *tmpc >> (MP_SIZEOF_BITS(mp_digit) - 1u); - /* Clear carry from T[i] */ - *tmpc++ &= MP_MASK; - } + /* Clear carry from T[i] */ + *tmpc++ &= MP_MASK; + } - /* clear digits above used (since we may not have grown result above) */ - for (i = c->used; i < olduse; i++) { - *tmpc++ = 0; - } - } + /* clear digits above used (since we may not have grown result above) */ + MP_ZERO_DIGITS(tmpc, olduse - c->used); + } - mp_clamp (c); - return MP_OKAY; + mp_clamp(c); + return MP_OKAY; } #endif - -/* ref: $Format:%D$ */ -/* git commit: $Format:%H$ */ -/* commit time: $Format:%ai$ */ |