1f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project#include <tommath.h> 2f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project#ifdef BN_MP_RSHD_C 3f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project/* LibTomMath, multiple-precision integer library -- Tom St Denis 4f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project * 5f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project * LibTomMath is a library that provides multiple-precision 6f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project * integer arithmetic as well as number theoretic functionality. 7f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project * 8f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project * The library was designed directly after the MPI library by 9f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project * Michael Fromberger but has been written from scratch with 10f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project * additional optimizations in place. 11f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project * 12f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project * The library is free for all purposes without any express 13f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project * guarantee it works. 14f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project * 15f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project * Tom St Denis, tomstdenis@gmail.com, http://math.libtomcrypt.com 16f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project */ 17f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project 18f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project/* shift right a certain amount of digits */ 19f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Projectvoid mp_rshd (mp_int * a, int b) 20f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project{ 21f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project int x; 22f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project 23f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project /* if b <= 0 then ignore it */ 24f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project if (b <= 0) { 25f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project return; 26f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project } 27f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project 28f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project /* if b > used then simply zero it and return */ 29f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project if (a->used <= b) { 30f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project mp_zero (a); 31f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project return; 32f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project } 33f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project 34f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project { 35f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project register mp_digit *bottom, *top; 36f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project 37f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project /* shift the digits down */ 38f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project 39f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project /* bottom */ 40f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project bottom = a->dp; 41f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project 42f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project /* top [offset into digits] */ 43f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project top = a->dp + b; 44f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project 45f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project /* this is implemented as a sliding window where 46f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project * the window is b-digits long and digits from 47f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project * the top of the window are copied to the bottom 48f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project * 49f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project * e.g. 50f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project 51f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project b-2 | b-1 | b0 | b1 | b2 | ... | bb | ----> 52f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project /\ | ----> 53f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project \-------------------/ ----> 54f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project */ 55f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project for (x = 0; x < (a->used - b); x++) { 56f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project *bottom++ = *top++; 57f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project } 58f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project 59f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project /* zero the top digits */ 60f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project for (; x < a->used; x++) { 61f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project *bottom++ = 0; 62f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project } 63f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project } 64f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project 65f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project /* remove excess digits */ 66f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project a->used -= b; 67f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project} 68f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project#endif 69f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project 70f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project/* $Source: /cvs/libtom/libtommath/bn_mp_rshd.c,v $ */ 71f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project/* $Revision: 1.3 $ */ 72f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project/* $Date: 2006/03/31 14:18:44 $ */ 73