Mercurial > dropbear

annotate libtommath/bn_mp_log_u32.c @ 1861:2b3a8026a6ce

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Add re-exec for server This allows ASLR to re-randomize the address space for every connection, preventing some vulnerabilities from being exploitable by repeated probing. Overhead (memory and time) is yet to be confirmed. At present this is only enabled on Linux. Other BSD platforms with fexecve() would probably also work though have not been tested.
author Matt Johnston <matt@ucc.asn.au>
date Sun, 30 Jan 2022 10:14:56 +0800
parents 1051e4eea25a
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
1692
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1 #include "tommath_private.h"
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2 #ifdef BN_MP_LOG_U32_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
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6 /* Compute log_{base}(a) */
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7 static mp_word s_pow(mp_word base, mp_word exponent)
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8 {
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9 mp_word result = 1uLL;
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10 while (exponent != 0u) {
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11 if ((exponent & 1u) == 1u) {
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12 result *= base;
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13 }
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14 exponent >>= 1;
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15 base *= base;
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16 }
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17
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18 return result;
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19 }
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20
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21 static mp_digit s_digit_ilogb(mp_digit base, mp_digit n)
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22 {
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23 mp_word bracket_low = 1uLL, bracket_mid, bracket_high, N;
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24 mp_digit ret, high = 1uL, low = 0uL, mid;
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25
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26 if (n < base) {
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27 return 0uL;
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28 }
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29 if (n == base) {
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30 return 1uL;
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31 }
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32
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33 bracket_high = (mp_word) base ;
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34 N = (mp_word) n;
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35
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36 while (bracket_high < N) {
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37 low = high;
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38 bracket_low = bracket_high;
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39 high <<= 1;
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40 bracket_high *= bracket_high;
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41 }
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42
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43 while (((mp_digit)(high - low)) > 1uL) {
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44 mid = (low + high) >> 1;
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45 bracket_mid = bracket_low * s_pow(base, (mp_word)(mid - low));
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46
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47 if (N < bracket_mid) {
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48 high = mid ;
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49 bracket_high = bracket_mid ;
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50 }
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51 if (N > bracket_mid) {
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52 low = mid ;
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53 bracket_low = bracket_mid ;
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54 }
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55 if (N == bracket_mid) {
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56 return (mp_digit) mid;
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57 }
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58 }
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59
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60 if (bracket_high == N) {
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61 ret = high;
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62 } else {
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63 ret = low;
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64 }
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65
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66 return ret;
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67 }
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68
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69 /* TODO: output could be "int" because the output of mp_radix_size is int, too,
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70 as is the output of mp_bitcount.
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71 With the same problem: max size is INT_MAX * MP_DIGIT not INT_MAX only!
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72 */
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73 mp_err mp_log_u32(const mp_int *a, uint32_t base, uint32_t *c)
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74 {
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75 mp_err err;
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76 mp_ord cmp;
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77 uint32_t high, low, mid;
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78 mp_int bracket_low, bracket_high, bracket_mid, t, bi_base;
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79
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80 err = MP_OKAY;
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81
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82 if (a->sign == MP_NEG) {
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83 return MP_VAL;
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84 }
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85
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86 if (MP_IS_ZERO(a)) {
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87 return MP_VAL;
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88 }
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89
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90 if (base < 2u) {
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91 return MP_VAL;
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92 }
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93
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94 /* A small shortcut for bases that are powers of two. */
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95 if ((base & (base - 1u)) == 0u) {
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96 int y, bit_count;
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97 for (y=0; (y < 7) && ((base & 1u) == 0u); y++) {
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98 base >>= 1;
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99 }
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100 bit_count = mp_count_bits(a) - 1;
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101 *c = (uint32_t)(bit_count/y);
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102 return MP_OKAY;
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103 }
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104
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105 if (a->used == 1) {
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106 *c = (uint32_t)s_digit_ilogb(base, a->dp[0]);
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107 return err;
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108 }
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109
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110 cmp = mp_cmp_d(a, base);
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111 if ((cmp == MP_LT) || (cmp == MP_EQ)) {
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112 *c = cmp == MP_EQ;
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113 return err;
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114 }
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115
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116 if ((err =
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117 mp_init_multi(&bracket_low, &bracket_high,
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118 &bracket_mid, &t, &bi_base, NULL)) != MP_OKAY) {
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119 return err;
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120 }
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121
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122 low = 0u;
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123 mp_set(&bracket_low, 1uL);
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124 high = 1u;
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125
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126 mp_set(&bracket_high, base);
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127
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128 /*
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129 A kind of Giant-step/baby-step algorithm.
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130 Idea shamelessly stolen from https://programmingpraxis.com/2010/05/07/integer-logarithms/2/
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131 The effect is asymptotic, hence needs benchmarks to test if the Giant-step should be skipped
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132 for small n.
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133 */
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
134 while (mp_cmp(&bracket_high, a) == MP_LT) {
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
135 low = high;
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
136 if ((err = mp_copy(&bracket_high, &bracket_low)) != MP_OKAY) {
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
137 goto LBL_ERR;
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
138 }
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
139 high <<= 1;
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
140 if ((err = mp_sqr(&bracket_high, &bracket_high)) != MP_OKAY) {
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
141 goto LBL_ERR;
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
142 }
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
143 }
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
144 mp_set(&bi_base, base);
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
145
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
146 while ((high - low) > 1u) {
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
147 mid = (high + low) >> 1;
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
148
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Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
149 if ((err = mp_expt_u32(&bi_base, (uint32_t)(mid - low), &t)) != MP_OKAY) {
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
150 goto LBL_ERR;
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
151 }
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
152 if ((err = mp_mul(&bracket_low, &t, &bracket_mid)) != MP_OKAY) {
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
153 goto LBL_ERR;
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
154 }
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
155 cmp = mp_cmp(a, &bracket_mid);
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
156 if (cmp == MP_LT) {
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
157 high = mid;
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
158 mp_exch(&bracket_mid, &bracket_high);
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
159 }
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
160 if (cmp == MP_GT) {
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
161 low = mid;
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
162 mp_exch(&bracket_mid, &bracket_low);
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
163 }
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
164 if (cmp == MP_EQ) {
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
165 *c = mid;
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
166 goto LBL_END;
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
167 }
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
168 }
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
169
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
170 *c = (mp_cmp(&bracket_high, a) == MP_EQ) ? high : low;
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
171
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
172 LBL_END:
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
173 LBL_ERR:
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
174 mp_clear_multi(&bracket_low, &bracket_high, &bracket_mid,
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
175 &t, &bi_base, NULL);
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
176 return err;
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
177 }
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
178
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
179
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
180 #endif