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annotate tomsfastmath/src/sqr/fp_sqr_comba_generic.c @ 647:939cd3e22c87 dropbear-tfm

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- Fix constraints so we don't get warned about uninitialised variable (it isn't used as input by the asm)
author Matt Johnston <matt@ucc.asn.au>
date Wed, 30 Nov 2011 23:15:21 +0800
parents a362b62d38b2
children
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1 /* TomsFastMath, a fast ISO C bignum library.
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2 *
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3 * This project is meant to fill in where LibTomMath
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4 * falls short. That is speed ;-)
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5 *
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6 * This project is public domain and free for all purposes.
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7 *
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8 * Tom St Denis, [email protected]
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9 */
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11 #define TFM_DEFINES
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12 #include "fp_sqr_comba.c"
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13
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14 /* generic comba squarer */
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15 void fp_sqr_comba(fp_int *A, fp_int *B)
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16 {
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17 int pa, ix, iz;
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18 fp_digit c0, c1, c2;
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19 fp_int tmp, *dst;
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20 #ifdef TFM_ISO
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21 fp_word tt;
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22 #endif
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24 /* get size of output and trim */
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25 pa = A->used + A->used;
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26 if (pa >= FP_SIZE) {
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27 pa = FP_SIZE-1;
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28 }
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29
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30 /* number of output digits to produce */
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31 COMBA_START;
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32 CLEAR_CARRY;
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34 if (A == B) {
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35 fp_zero(&tmp);
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36 dst = &tmp;
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37 } else {
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38 fp_zero(B);
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39 dst = B;
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40 }
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41
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42 for (ix = 0; ix < pa; ix++) {
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43 int tx, ty, iy;
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44 fp_digit *tmpy, *tmpx;
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45
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46 /* get offsets into the two bignums */
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47 ty = MIN(A->used-1, ix);
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48 tx = ix - ty;
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49
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50 /* setup temp aliases */
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51 tmpx = A->dp + tx;
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52 tmpy = A->dp + ty;
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53
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54 /* this is the number of times the loop will iterrate,
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55 while (tx++ < a->used && ty-- >= 0) { ... }
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56 */
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57 iy = MIN(A->used-tx, ty+1);
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58
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59 /* now for squaring tx can never equal ty
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60 * we halve the distance since they approach
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61 * at a rate of 2x and we have to round because
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62 * odd cases need to be executed
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63 */
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64 iy = MIN(iy, (ty-tx+1)>>1);
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65
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66 /* forward carries */
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67 CARRY_FORWARD;
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68
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69 /* execute loop */
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70 for (iz = 0; iz < iy; iz++) {
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71 SQRADD2(*tmpx++, *tmpy--);
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72 }
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73
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74 /* even columns have the square term in them */
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75 if ((ix&1) == 0) {
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76 SQRADD(A->dp[ix>>1], A->dp[ix>>1]);
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77 }
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78
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79 /* store it */
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80 COMBA_STORE(dst->dp[ix]);
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81 }
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82
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83 COMBA_FINI;
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84
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85 /* setup dest */
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86 dst->used = pa;
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87 fp_clamp (dst);
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88 if (dst != B) {
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89 fp_copy(dst, B);
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90 }
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91 }
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92
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93 /* $Source$ */
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94 /* $Revision$ */
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95 /* $Date$ */