tommath/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.
*
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* Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org
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*/
#include <tommath.h>
/* high level addition (handles signs) */
int
mp_add (mp_int * a, mp_int * b, mp_int * c)
{
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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;
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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. */
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if (mp_cmp_mag (a, b) == MP_LT) {
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c->sign = sb;
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res = s_mp_sub (b, a, c);
} else {
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c->sign = sa;
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res = s_mp_sub (a, b, c);
}
}
return res;
}
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