1f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project#include <tommath.h> 2f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project#ifdef BN_MP_DIV_2_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/* b = a/2 */ 19f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Projectint mp_div_2(mp_int * a, mp_int * b) 20f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project{ 21f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project int x, res, oldused; 22f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project 23f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project /* copy */ 24f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project if (b->alloc < a->used) { 25f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project if ((res = mp_grow (b, a->used)) != MP_OKAY) { 26f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project return res; 27f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project } 28f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project } 29f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project 30f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project oldused = b->used; 31f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project b->used = a->used; 32f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project { 33f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project register mp_digit r, rr, *tmpa, *tmpb; 34f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project 35f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project /* source alias */ 36f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project tmpa = a->dp + b->used - 1; 37f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project 38f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project /* dest alias */ 39f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project tmpb = b->dp + b->used - 1; 40f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project 41f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project /* carry */ 42f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project r = 0; 43f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project for (x = b->used - 1; x >= 0; x--) { 44f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project /* get the carry for the next iteration */ 45f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project rr = *tmpa & 1; 46f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project 47f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project /* shift the current digit, add in carry and store */ 48f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project *tmpb-- = (*tmpa-- >> 1) | (r << (DIGIT_BIT - 1)); 49f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project 50f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project /* forward carry to next iteration */ 51f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project r = rr; 52f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project } 53f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project 54f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project /* zero excess digits */ 55f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project tmpb = b->dp + b->used; 56f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project for (x = b->used; x < oldused; x++) { 57f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project *tmpb++ = 0; 58f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project } 59f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project } 60f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project b->sign = a->sign; 61f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project mp_clamp (b); 62f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project return MP_OKAY; 63f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project} 64f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project#endif 65f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project 66f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project/* $Source: /cvs/libtom/libtommath/bn_mp_div_2.c,v $ */ 67f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project/* $Revision: 1.3 $ */ 68f7fc46c63fdc8f39234fea409b8dbe116d73ebf8The Android Open Source Project/* $Date: 2006/03/31 14:18:44 $ */ 69