tommath/bn_mp_div_2d.c

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#include <tommath_private.h>
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#ifdef BN_MP_DIV_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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*/
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/* shift right by a certain bit count (store quotient in c, optional remainder in d) */
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int mp_div_2d (mp_int * a, int b, mp_int * c, mp_int * d)
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{
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mp_digit D, r, rr;
int x, res;
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/* if the shift count is <= 0 then we do no work */
if (b <= 0) {
res = mp_copy (a, c);
if (d != NULL) {
mp_zero (d);
}
return res;
}
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/* copy */
if ((res = mp_copy (a, c)) != MP_OKAY) {
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return res;
}
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/* 'a' should not be used after here - it might be the same as d */
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/* get the remainder */
if (d != NULL) {
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if ((res = mp_mod_2d (a, b, d)) != MP_OKAY) {
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return res;
}
}
/* shift by as many digits in the bit count */
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if (b >= (int)DIGIT_BIT) {
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mp_rshd (c, b / DIGIT_BIT);
}
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/* shift any bit count < DIGIT_BIT */
D = (mp_digit) (b % DIGIT_BIT);
if (D != 0) {
mp_digit *tmpc, mask, shift;
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/* mask */
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mask = (((mp_digit)1) << D) - 1;
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/* shift for lsb */
shift = DIGIT_BIT - D;
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/* alias */
tmpc = c->dp + (c->used - 1);
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/* carry */
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r = 0;
for (x = c->used - 1; x >= 0; x--) {
/* get the lower bits of this word in a temp */
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rr = *tmpc & mask;
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/* shift the current word and mix in the carry bits from the previous word */
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*tmpc = (*tmpc >> D) | (r << shift);
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--tmpc;
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/* set the carry to the carry bits of the current word found above */
r = rr;
}
}
mp_clamp (c);
return MP_OKAY;
}
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#endif
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/* ref: $Format:%D$ */
/* git commit: $Format:%H$ */
/* commit time: $Format:%ai$ */