Mercurial > dropbear

annotate libtommath/bn_mp_log_u32.c @ 1715:3974f087d9c0

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Disallow leading lines before the ident for server (#102) Per RFC4253 4.2 clients must be able to process other lines of data before the version string, server behavior is not defined neither with MUST/SHOULD nor with MAY. If server process up to 50 lines too - it may cause too long hanging session with invalid/evil client that consume host resources and potentially may lead to DDoS on poor embedded boxes. Let's require first line from client to be version string and fail early if it's not - matches both RFC and real OpenSSH behavior.
author Vladislav Grishenko <themiron@users.noreply.github.com>
date Mon, 15 Jun 2020 18:22:18 +0500
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 */
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134 while (mp_cmp(&bracket_high, a) == MP_LT) {
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135 low = high;
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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:
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137 goto LBL_ERR;
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Steffen Jaeckel <s@jaeckel.eu>
parents:
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138 }
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
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139 high <<= 1;
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Steffen Jaeckel <s@jaeckel.eu>
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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:
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141 goto LBL_ERR;
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Steffen Jaeckel <s@jaeckel.eu>
parents:
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142 }
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Steffen Jaeckel <s@jaeckel.eu>
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143 }
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Steffen Jaeckel <s@jaeckel.eu>
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144 mp_set(&bi_base, base);
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Steffen Jaeckel <s@jaeckel.eu>
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145
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Steffen Jaeckel <s@jaeckel.eu>
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146 while ((high - low) > 1u) {
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Steffen Jaeckel <s@jaeckel.eu>
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147 mid = (high + low) >> 1;
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Steffen Jaeckel <s@jaeckel.eu>
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148
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149 if ((err = mp_expt_u32(&bi_base, (uint32_t)(mid - low), &t)) != MP_OKAY) {
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Steffen Jaeckel <s@jaeckel.eu>
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150 goto LBL_ERR;
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Steffen Jaeckel <s@jaeckel.eu>
parents:
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151 }
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Steffen Jaeckel <s@jaeckel.eu>
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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;
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Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
154 }
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Steffen Jaeckel <s@jaeckel.eu>
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155 cmp = mp_cmp(a, &bracket_mid);
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Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
156 if (cmp == MP_LT) {
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Steffen Jaeckel <s@jaeckel.eu>
parents:
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157 high = mid;
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Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
158 mp_exch(&bracket_mid, &bracket_high);
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Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
159 }
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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;
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Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
162 mp_exch(&bracket_mid, &bracket_low);
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Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
163 }
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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;
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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:
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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;
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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