Mercurial > dropbear

annotate libtommath/bn_s_mp_sqr.c @ 786:e76614145aea DROPBEAR_2013.58

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2013.58
author Matt Johnston <matt@ucc.asn.au>
date Thu, 18 Apr 2013 22:57:47 +0800
parents 5ff8218bcee9
children 60fc6476e044
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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1 #include <tommath.h>
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2 #ifdef BN_S_MP_SQR_C
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3 /* LibTomMath, multiple-precision integer library -- Tom St Denis
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4 *
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5 * LibTomMath is a library that provides multiple-precision
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6 * integer arithmetic as well as number theoretic functionality.
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7 *
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8 * The library was designed directly after the MPI library by
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9 * Michael Fromberger but has been written from scratch with
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10 * additional optimizations in place.
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11 *
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12 * The library is free for all purposes without any express
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13 * guarantee it works.
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14 *
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15 * Tom St Denis, [email protected], http://math.libtomcrypt.com
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16 */
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17
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18 /* low level squaring, b = a*a, HAC pp.596-597, Algorithm 14.16 */
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19 int s_mp_sqr (mp_int * a, mp_int * b)
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20 {
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21 mp_int t;
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22 int res, ix, iy, pa;
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23 mp_word r;
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24 mp_digit u, tmpx, *tmpt;
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25
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26 pa = a->used;
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27 if ((res = mp_init_size (&t, 2*pa + 1)) != MP_OKAY) {
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28 return res;
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29 }
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30
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31 /* default used is maximum possible size */
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32 t.used = 2*pa + 1;
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33
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34 for (ix = 0; ix < pa; ix++) {
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35 /* first calculate the digit at 2*ix */
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36 /* calculate double precision result */
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37 r = ((mp_word) t.dp[2*ix]) +
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38 ((mp_word)a->dp[ix])*((mp_word)a->dp[ix]);
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39
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40 /* store lower part in result */
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41 t.dp[ix+ix] = (mp_digit) (r & ((mp_word) MP_MASK));
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42
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43 /* get the carry */
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44 u = (mp_digit)(r >> ((mp_word) DIGIT_BIT));
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45
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46 /* left hand side of A[ix] * A[iy] */
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47 tmpx = a->dp[ix];
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48
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49 /* alias for where to store the results */
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50 tmpt = t.dp + (2*ix + 1);
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51
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52 for (iy = ix + 1; iy < pa; iy++) {
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53 /* first calculate the product */
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54 r = ((mp_word)tmpx) * ((mp_word)a->dp[iy]);
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55
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56 /* now calculate the double precision result, note we use
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57 * addition instead of *2 since it's easier to optimize
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58 */
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59 r = ((mp_word) *tmpt) + r + r + ((mp_word) u);
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60
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61 /* store lower part */
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62 *tmpt++ = (mp_digit) (r & ((mp_word) MP_MASK));
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63
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64 /* get carry */
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65 u = (mp_digit)(r >> ((mp_word) DIGIT_BIT));
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66 }
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67 /* propagate upwards */
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68 while (u != ((mp_digit) 0)) {
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69 r = ((mp_word) *tmpt) + ((mp_word) u);
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70 *tmpt++ = (mp_digit) (r & ((mp_word) MP_MASK));
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71 u = (mp_digit)(r >> ((mp_word) DIGIT_BIT));
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72 }
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73 }
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74
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75 mp_clamp (&t);
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76 mp_exch (&t, b);
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77 mp_clear (&t);
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78 return MP_OKAY;
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79 }
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80 #endif
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81
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82 /* $Source: /cvs/libtom/libtommath/bn_s_mp_sqr.c,v $ */
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83 /* $Revision: 1.3 $ */
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84 /* $Date: 2006/03/31 14:18:44 $ */