tommath/bn_mp_add.c

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#include <tommath_private.h>
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#ifdef BN_MP_ADD_C
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/* LibTomMath, multiple-precision integer library -- Tom St Denis
*
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* LibTomMath is a library that provides multiple-precision
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* integer arithmetic as well as number theoretic functionality.
*
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* The library was designed directly after the MPI library by
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* 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
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*/
/* high level addition (handles signs) */
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int mp_add (mp_int * a, mp_int * b, mp_int * c)
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{
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int sa, sb, res;
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/* get sign of both inputs */
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sa = a->sign;
sb = b->sign;
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/* handle two cases, not four */
if (sa == sb) {
/* both positive or both negative */
/* add their magnitudes, copy the sign */
c->sign = sa;
res = s_mp_add(a, b, c);
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} else {
/* one positive, the other negative */
/* subtract the one with the greater magnitude from */
/* the one of the lesser magnitude. The result gets */
/* the sign of the one with the greater magnitude. */
if (mp_cmp_mag(a, b) == MP_LT) {
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c->sign = sb;
res = s_mp_sub(b, a, c);
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} else {
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c->sign = sa;
res = s_mp_sub(a, b, c);
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}
}
return res;
}
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#endif
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