diff options
Diffstat (limited to 'libtommath/bn_mp_rshd.c')
| -rw-r--r-- | libtommath/bn_mp_rshd.c | 62 |
1 files changed, 22 insertions, 40 deletions
diff --git a/libtommath/bn_mp_rshd.c b/libtommath/bn_mp_rshd.c index 53fb424..bb8743e 100644 --- a/libtommath/bn_mp_rshd.c +++ b/libtommath/bn_mp_rshd.c @@ -1,21 +1,13 @@ #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 - * additional optimizations in place. - * - * SPDX-License-Identifier: Unlicense - */ +/* LibTomMath, multiple-precision integer library -- Tom St Denis */ +/* SPDX-License-Identifier: Unlicense */ /* shift right a certain amount of digits */ void mp_rshd(mp_int *a, int b) { int x; + mp_digit *bottom, *top; /* if b <= 0 then ignore it */ if (b <= 0) { @@ -28,42 +20,32 @@ void mp_rshd(mp_int *a, int b) return; } - { - mp_digit *bottom, *top; + /* shift the digits down */ - /* shift the digits down */ + /* bottom */ + bottom = a->dp; - /* bottom */ - bottom = a->dp; + /* top [offset into digits] */ + top = a->dp + b; - /* 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. - /* 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; - } + b-2 | b-1 | b0 | b1 | b2 | ... | bb | ----> + /\ | ----> + \-------------------/ ----> + */ + for (x = 0; x < (a->used - b); x++) { + *bottom++ = *top++; } + /* zero the top digits */ + MP_ZERO_DIGITS(bottom, a->used - x); + /* remove excess digits */ a->used -= b; } #endif - -/* ref: HEAD -> master, tag: v1.1.0 */ -/* git commit: 08549ad6bc8b0cede0b357a9c341c5c6473a9c55 */ -/* commit time: 2019-01-28 20:32:32 +0100 */ |