view libtommath/bn_mp_rshd.c @ 1436:60fc6476e044

Update to libtommath v1.0
author Matt Johnston Sat, 24 Jun 2017 22:37:14 +0800 5ff8218bcee9 8bba51a55704
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```#include <tommath_private.h>
#ifdef BN_MP_RSHD_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis
*
* LibTomMath is a library that provides multiple-precision
* integer arithmetic as well as number theoretic functionality.
*
* The library was designed directly after the MPI library by
* Michael Fromberger but has been written from scratch with
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, [email protected], http://libtom.org
*/

/* shift right a certain amount of digits */
void mp_rshd (mp_int * a, int b)
{
int     x;

/* if b <= 0 then ignore it */
if (b <= 0) {
return;
}

/* if b > used then simply zero it and return */
if (a->used <= b) {
mp_zero (a);
return;
}

{
mp_digit *bottom, *top;

/* shift the digits down */

/* bottom */
bottom = a->dp;

/* top [offset into digits] */
top = a->dp + b;

/* this is implemented as a sliding window where
* the window is b-digits long and digits from
* the top of the window are copied to the bottom
*
* e.g.

b-2 | b-1 | b0 | b1 | b2 | ... | bb |   ---->
/\                   |      ---->
\-------------------/      ---->
*/
for (x = 0; x < (a->used - b); x++) {
*bottom++ = *top++;
}

/* zero the top digits */
for (; x < a->used; x++) {
*bottom++ = 0;
}
}

/* remove excess digits */
a->used -= b;
}
#endif

/* \$Source\$ */
/* \$Revision\$ */
/* \$Date\$ */
```