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author | Kevin B Kenny <kennykb@acm.org> | 2005-01-19 22:41:26 (GMT) |
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committer | Kevin B Kenny <kennykb@acm.org> | 2005-01-19 22:41:26 (GMT) |
commit | b9cf65a08e6a59e434685e894e3189c201ac6791 (patch) | |
tree | 1f0868ef44c9f17d83d10dc94343df7b8cfe1842 /libtommath/bn_s_mp_add.c | |
parent | c6a259aeeca4814a97cf6694814c63e74e4e18fa (diff) | |
download | tcl-b9cf65a08e6a59e434685e894e3189c201ac6791.zip tcl-b9cf65a08e6a59e434685e894e3189c201ac6791.tar.gz tcl-b9cf65a08e6a59e434685e894e3189c201ac6791.tar.bz2 |
Import of libtommath 0.33
Diffstat (limited to 'libtommath/bn_s_mp_add.c')
-rw-r--r-- | libtommath/bn_s_mp_add.c | 105 |
1 files changed, 105 insertions, 0 deletions
diff --git a/libtommath/bn_s_mp_add.c b/libtommath/bn_s_mp_add.c new file mode 100644 index 0000000..2b378ae --- /dev/null +++ b/libtommath/bn_s_mp_add.c @@ -0,0 +1,105 @@ +#include <tommath.h> +#ifdef BN_S_MP_ADD_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 + */ + +/* low level addition, based on HAC pp.594, Algorithm 14.7 */ +int +s_mp_add (mp_int * a, mp_int * b, mp_int * c) +{ + mp_int *x; + int olduse, res, 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 ((res = mp_grow (c, max + 1)) != MP_OKAY) { + return res; + } + } + + /* get old used digit count and set new one */ + olduse = c->used; + c->used = max + 1; + + { + register mp_digit u, *tmpa, *tmpb, *tmpc; + register 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)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)DIGIT_BIT); + + /* take away carry bit from T[i] */ + *tmpc++ &= MP_MASK; + } + } + + /* add carry */ + *tmpc++ = u; + + /* clear digits above oldused */ + for (i = c->used; i < olduse; i++) { + *tmpc++ = 0; + } + } + + mp_clamp (c); + return MP_OKAY; +} +#endif |