1/* $NetBSD: bn_s_mp_sqr.c,v 1.2 2017/01/28 21:31:47 christos Exp $ */ 2 3#include <tommath.h> 4#ifdef BN_S_MP_SQR_C 5/* LibTomMath, multiple-precision integer library -- Tom St Denis 6 * 7 * LibTomMath is a library that provides multiple-precision 8 * integer arithmetic as well as number theoretic functionality. 9 * 10 * The library was designed directly after the MPI library by 11 * Michael Fromberger but has been written from scratch with 12 * additional optimizations in place. 13 * 14 * The library is free for all purposes without any express 15 * guarantee it works. 16 * 17 * Tom St Denis, tomstdenis@gmail.com, http://libtom.org 18 */ 19 20/* low level squaring, b = a*a, HAC pp.596-597, Algorithm 14.16 */ 21int s_mp_sqr (mp_int * a, mp_int * b) 22{ 23 mp_int t; 24 int res, ix, iy, pa; 25 mp_word r; 26 mp_digit u, tmpx, *tmpt; 27 28 pa = a->used; 29 if ((res = mp_init_size (&t, 2*pa + 1)) != MP_OKAY) { 30 return res; 31 } 32 33 /* default used is maximum possible size */ 34 t.used = 2*pa + 1; 35 36 for (ix = 0; ix < pa; ix++) { 37 /* first calculate the digit at 2*ix */ 38 /* calculate double precision result */ 39 r = ((mp_word) t.dp[2*ix]) + 40 ((mp_word)a->dp[ix])*((mp_word)a->dp[ix]); 41 42 /* store lower part in result */ 43 t.dp[ix+ix] = (mp_digit) (r & ((mp_word) MP_MASK)); 44 45 /* get the carry */ 46 u = (mp_digit)(r >> ((mp_word) DIGIT_BIT)); 47 48 /* left hand side of A[ix] * A[iy] */ 49 tmpx = a->dp[ix]; 50 51 /* alias for where to store the results */ 52 tmpt = t.dp + (2*ix + 1); 53 54 for (iy = ix + 1; iy < pa; iy++) { 55 /* first calculate the product */ 56 r = ((mp_word)tmpx) * ((mp_word)a->dp[iy]); 57 58 /* now calculate the double precision result, note we use 59 * addition instead of *2 since it's easier to optimize 60 */ 61 r = ((mp_word) *tmpt) + r + r + ((mp_word) u); 62 63 /* store lower part */ 64 *tmpt++ = (mp_digit) (r & ((mp_word) MP_MASK)); 65 66 /* get carry */ 67 u = (mp_digit)(r >> ((mp_word) DIGIT_BIT)); 68 } 69 /* propagate upwards */ 70 while (u != ((mp_digit) 0)) { 71 r = ((mp_word) *tmpt) + ((mp_word) u); 72 *tmpt++ = (mp_digit) (r & ((mp_word) MP_MASK)); 73 u = (mp_digit)(r >> ((mp_word) DIGIT_BIT)); 74 } 75 } 76 77 mp_clamp (&t); 78 mp_exch (&t, b); 79 mp_clear (&t); 80 return MP_OKAY; 81} 82#endif 83 84/* Source: /cvs/libtom/libtommath/bn_s_mp_sqr.c,v */ 85/* Revision: 1.4 */ 86/* Date: 2006/12/28 01:25:13 */ 87