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annotate libtommath/bn_s_mp_karatsuba_sqr.c @ 1900:6110afb6f581

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author Matt Johnston <matt@ucc.asn.au>
date Thu, 24 Mar 2022 12:22:07 +0800
parents 1051e4eea25a
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
1692
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
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1 #include "tommath_private.h"
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
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2 #ifdef BN_S_MP_KARATSUBA_SQR_C
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3 /* LibTomMath, multiple-precision integer library -- Tom St Denis */
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4 /* SPDX-License-Identifier: Unlicense */
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5
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
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6 /* Karatsuba squaring, computes b = a*a using three
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
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7 * half size squarings
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8 *
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
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9 * See comments of karatsuba_mul for details. It
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10 * is essentially the same algorithm but merely
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11 * tuned to perform recursive squarings.
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12 */
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13 mp_err s_mp_karatsuba_sqr(const mp_int *a, mp_int *b)
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14 {
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
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15 mp_int x0, x1, t1, t2, x0x0, x1x1;
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
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16 int B;
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17 mp_err err = MP_MEM;
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18
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19 /* min # of digits */
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20 B = a->used;
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21
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22 /* now divide in two */
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23 B = B >> 1;
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24
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25 /* init copy all the temps */
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26 if (mp_init_size(&x0, B) != MP_OKAY)
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27 goto LBL_ERR;
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28 if (mp_init_size(&x1, a->used - B) != MP_OKAY)
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29 goto X0;
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30
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31 /* init temps */
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32 if (mp_init_size(&t1, a->used * 2) != MP_OKAY)
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33 goto X1;
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34 if (mp_init_size(&t2, a->used * 2) != MP_OKAY)
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35 goto T1;
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36 if (mp_init_size(&x0x0, B * 2) != MP_OKAY)
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37 goto T2;
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38 if (mp_init_size(&x1x1, (a->used - B) * 2) != MP_OKAY)
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39 goto X0X0;
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40
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41 {
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42 int x;
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43 mp_digit *dst, *src;
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44
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45 src = a->dp;
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46
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47 /* now shift the digits */
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48 dst = x0.dp;
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49 for (x = 0; x < B; x++) {
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50 *dst++ = *src++;
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51 }
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52
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53 dst = x1.dp;
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54 for (x = B; x < a->used; x++) {
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55 *dst++ = *src++;
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56 }
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57 }
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58
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59 x0.used = B;
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60 x1.used = a->used - B;
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61
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62 mp_clamp(&x0);
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63
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64 /* now calc the products x0*x0 and x1*x1 */
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65 if (mp_sqr(&x0, &x0x0) != MP_OKAY)
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66 goto X1X1; /* x0x0 = x0*x0 */
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67 if (mp_sqr(&x1, &x1x1) != MP_OKAY)
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68 goto X1X1; /* x1x1 = x1*x1 */
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69
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70 /* now calc (x1+x0)**2 */
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71 if (s_mp_add(&x1, &x0, &t1) != MP_OKAY)
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72 goto X1X1; /* t1 = x1 - x0 */
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73 if (mp_sqr(&t1, &t1) != MP_OKAY)
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74 goto X1X1; /* t1 = (x1 - x0) * (x1 - x0) */
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75
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76 /* add x0y0 */
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77 if (s_mp_add(&x0x0, &x1x1, &t2) != MP_OKAY)
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78 goto X1X1; /* t2 = x0x0 + x1x1 */
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79 if (s_mp_sub(&t1, &t2, &t1) != MP_OKAY)
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80 goto X1X1; /* t1 = (x1+x0)**2 - (x0x0 + x1x1) */
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81
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82 /* shift by B */
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83 if (mp_lshd(&t1, B) != MP_OKAY)
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84 goto X1X1; /* t1 = (x0x0 + x1x1 - (x1-x0)*(x1-x0))<<B */
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85 if (mp_lshd(&x1x1, B * 2) != MP_OKAY)
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86 goto X1X1; /* x1x1 = x1x1 << 2*B */
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87
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88 if (mp_add(&x0x0, &t1, &t1) != MP_OKAY)
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89 goto X1X1; /* t1 = x0x0 + t1 */
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90 if (mp_add(&t1, &x1x1, b) != MP_OKAY)
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91 goto X1X1; /* t1 = x0x0 + t1 + x1x1 */
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92
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93 err = MP_OKAY;
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94
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95 X1X1:
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96 mp_clear(&x1x1);
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97 X0X0:
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98 mp_clear(&x0x0);
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99 T2:
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100 mp_clear(&t2);
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101 T1:
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102 mp_clear(&t1);
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103 X1:
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104 mp_clear(&x1);
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105 X0:
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106 mp_clear(&x0);
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107 LBL_ERR:
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108 return err;
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109 }
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110 #endif