62 lines
1.5 KiB
C
62 lines
1.5 KiB
C
/* LibTomMath, multiple-precision integer library -- Tom St Denis
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*
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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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*
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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
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* additional optimizations in place.
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*
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* The library is free for all purposes without any express
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* guarantee it works.
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*
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* Tom St Denis, tomstdenis@iahu.ca, http://math.libtomcrypt.org
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*/
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#include <tommath.h>
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/* shift left a certain amount of digits */
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int mp_lshd (mp_int * a, int b)
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{
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int x, res;
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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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/* grow to fit the new digits */
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if (a->alloc < a->used + b) {
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if ((res = mp_grow (a, a->used + b)) != MP_OKAY) {
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return res;
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}
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}
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{
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register mp_digit *top, *bottom;
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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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top = a->dp;
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for (x = 0; x < b; x++) {
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*top++ = 0;
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}
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}
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return MP_OKAY;
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}
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