diff options
Diffstat (limited to 'third_party/heimdal/lib/hcrypto/libtommath/bn_s_mp_add.c')
-rw-r--r-- | third_party/heimdal/lib/hcrypto/libtommath/bn_s_mp_add.c | 91 |
1 files changed, 91 insertions, 0 deletions
diff --git a/third_party/heimdal/lib/hcrypto/libtommath/bn_s_mp_add.c b/third_party/heimdal/lib/hcrypto/libtommath/bn_s_mp_add.c new file mode 100644 index 0000000..c946aa8 --- /dev/null +++ b/third_party/heimdal/lib/hcrypto/libtommath/bn_s_mp_add.c @@ -0,0 +1,91 @@ +#include "tommath_private.h" +#ifdef BN_S_MP_ADD_C +/* LibTomMath, multiple-precision integer library -- Tom St Denis */ +/* SPDX-License-Identifier: Unlicense */ + +/* low level addition, based on HAC pp.594, Algorithm 14.7 */ +mp_err s_mp_add(const mp_int *a, const mp_int *b, mp_int *c) +{ + const mp_int *x; + mp_err err; + int olduse, min, max; + + /* find sizes, we let |a| <= |b| which means we have to sort + * them. "x" will point to the input with the most digits + */ + if (a->used > b->used) { + min = b->used; + max = a->used; + x = a; + } else { + min = a->used; + max = b->used; + x = b; + } + + /* init result */ + if (c->alloc < (max + 1)) { + if ((err = mp_grow(c, max + 1)) != MP_OKAY) { + return err; + } + } + + /* get old used digit count and set new one */ + olduse = c->used; + c->used = max + 1; + + { + mp_digit u, *tmpa, *tmpb, *tmpc; + int i; + + /* alias for digit pointers */ + + /* first input */ + tmpa = a->dp; + + /* second input */ + tmpb = b->dp; + + /* destination */ + tmpc = c->dp; + + /* zero the carry */ + u = 0; + for (i = 0; i < min; i++) { + /* Compute the sum at one digit, T[i] = A[i] + B[i] + U */ + *tmpc = *tmpa++ + *tmpb++ + u; + + /* U = carry bit of T[i] */ + u = *tmpc >> (mp_digit)MP_DIGIT_BIT; + + /* take away carry bit from T[i] */ + *tmpc++ &= MP_MASK; + } + + /* now copy higher words if any, that is in A+B + * if A or B has more digits add those in + */ + if (min != max) { + for (; i < max; i++) { + /* T[i] = X[i] + U */ + *tmpc = x->dp[i] + u; + + /* U = carry bit of T[i] */ + u = *tmpc >> (mp_digit)MP_DIGIT_BIT; + + /* take away carry bit from T[i] */ + *tmpc++ &= MP_MASK; + } + } + + /* add carry */ + *tmpc++ = u; + + /* clear digits above oldused */ + MP_ZERO_DIGITS(tmpc, olduse - c->used); + } + + mp_clamp(c); + return MP_OKAY; +} +#endif |