1af0de1f91
* same behavior for positive numbers * generalisation for negative numbers, treating them as two complement * improve algorithm, iterate once over the digits, manually perform two complement * simplify mp_add_d, mp_sub_d * functions are safe in case of a==c or b==c * renamed mp_tc_div_2d to mp_signed_rsh (signed right shift)
52 lines
1.1 KiB
C
52 lines
1.1 KiB
C
#include "tommath_private.h"
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#ifdef BN_MP_LSHD_C
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/* LibTomMath, multiple-precision integer library -- Tom St Denis */
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/* SPDX-License-Identifier: Unlicense */
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/* shift left a certain amount of digits */
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mp_err mp_lshd(mp_int *a, int b)
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{
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int x;
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mp_err err;
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mp_digit *top, *bottom;
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/* if its less than zero return */
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if (b <= 0) {
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return MP_OKAY;
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}
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/* no need to shift 0 around */
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if (MP_IS_ZERO(a)) {
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return MP_OKAY;
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}
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/* grow to fit the new digits */
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if (a->alloc < (a->used + b)) {
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if ((err = mp_grow(a, a->used + b)) != MP_OKAY) {
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return err;
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}
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}
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/* increment the used by the shift amount then copy upwards */
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a->used += b;
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/* top */
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top = a->dp + a->used - 1;
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/* base */
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bottom = (a->dp + a->used - 1) - b;
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/* much like mp_rshd this is implemented using a sliding window
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* except the window goes the otherway around. Copying from
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* the bottom to the top. see bn_mp_rshd.c for more info.
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*/
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for (x = a->used - 1; x >= b; x--) {
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*top-- = *bottom--;
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}
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/* zero the lower digits */
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MP_ZERO_DIGITS(a->dp, b);
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return MP_OKAY;
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}
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#endif
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