tommath/bn_mp_mul_2d.c

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#include <tommath_private.h>
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#ifdef BN_MP_MUL_2D_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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*/
/* shift left by a certain bit count */
int mp_mul_2d(const mp_int *a, int b, mp_int *c)
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{
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mp_digit d;
int res;
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/* copy */
if (a != c) {
if ((res = mp_copy(a, c)) != MP_OKAY) {
return res;
}
}
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if (c->alloc < (c->used + (b / DIGIT_BIT) + 1)) {
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if ((res = mp_grow(c, c->used + (b / DIGIT_BIT) + 1)) != MP_OKAY) {
return res;
}
}
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/* shift by as many digits in the bit count */
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if (b >= DIGIT_BIT) {
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if ((res = mp_lshd(c, b / DIGIT_BIT)) != MP_OKAY) {
return res;
}
}
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/* shift any bit count < DIGIT_BIT */
d = (mp_digit)(b % DIGIT_BIT);
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if (d != 0u) {
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mp_digit *tmpc, shift, mask, r, rr;
int x;
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/* bitmask for carries */
mask = ((mp_digit)1 << d) - (mp_digit)1;
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/* shift for msbs */
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shift = (mp_digit)DIGIT_BIT - d;
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/* alias */
tmpc = c->dp;
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/* carry */
r = 0;
for (x = 0; x < c->used; x++) {
/* get the higher bits of the current word */
rr = (*tmpc >> shift) & mask;
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/* shift the current word and OR in the carry */
*tmpc = ((*tmpc << d) | r) & MP_MASK;
++tmpc;
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/* set the carry to the carry bits of the current word */
r = rr;
}
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/* set final carry */
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if (r != 0u) {
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c->dp[(c->used)++] = r;
}
}
mp_clamp(c);
return MP_OKAY;
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}
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#endif
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/* ref: $Format:%D$ */
/* git commit: $Format:%H$ */
/* commit time: $Format:%ai$ */