[331] | 1 | /*
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| 2 | * Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
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| 3 | *
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| 4 | * Licensed under the OpenSSL license (the "License"). You may not use
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| 5 | * this file except in compliance with the License. You can obtain a copy
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| 6 | * in the file LICENSE in the source distribution or at
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| 7 | * https://www.openssl.org/source/license.html
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| 8 | */
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| 9 |
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| 10 | #include "internal/cryptlib.h"
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| 11 | #include "bn_lcl.h"
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| 12 |
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| 13 | BN_ULONG BN_mod_word(const BIGNUM *a, BN_ULONG w)
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| 14 | {
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| 15 | #ifndef BN_LLONG
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| 16 | BN_ULONG ret = 0;
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| 17 | #else
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| 18 | BN_ULLONG ret = 0;
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| 19 | #endif
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| 20 | int i;
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| 21 |
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| 22 | if (w == 0)
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| 23 | return (BN_ULONG)-1;
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| 24 |
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| 25 | #ifndef BN_LLONG
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| 26 | /*
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| 27 | * If |w| is too long and we don't have BN_ULLONG then we need to fall
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| 28 | * back to using BN_div_word
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| 29 | */
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| 30 | if (w > ((BN_ULONG)1 << BN_BITS4)) {
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| 31 | BIGNUM *tmp = BN_dup(a);
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| 32 | if (tmp == NULL)
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| 33 | return (BN_ULONG)-1;
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| 34 |
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| 35 | ret = BN_div_word(tmp, w);
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| 36 | BN_free(tmp);
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| 37 |
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| 38 | return ret;
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| 39 | }
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| 40 | #endif
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| 41 |
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| 42 | bn_check_top(a);
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| 43 | w &= BN_MASK2;
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| 44 | for (i = a->top - 1; i >= 0; i--) {
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| 45 | #ifndef BN_LLONG
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| 46 | /*
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| 47 | * We can assume here that | w <= ((BN_ULONG)1 << BN_BITS4) | and so
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| 48 | * | ret < ((BN_ULONG)1 << BN_BITS4) | and therefore the shifts here are
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| 49 | * safe and will not overflow
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| 50 | */
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| 51 | ret = ((ret << BN_BITS4) | ((a->d[i] >> BN_BITS4) & BN_MASK2l)) % w;
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| 52 | ret = ((ret << BN_BITS4) | (a->d[i] & BN_MASK2l)) % w;
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| 53 | #else
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| 54 | ret = (BN_ULLONG) (((ret << (BN_ULLONG) BN_BITS2) | a->d[i]) %
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| 55 | (BN_ULLONG) w);
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| 56 | #endif
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| 57 | }
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| 58 | return ((BN_ULONG)ret);
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| 59 | }
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| 60 |
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| 61 | BN_ULONG BN_div_word(BIGNUM *a, BN_ULONG w)
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| 62 | {
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| 63 | BN_ULONG ret = 0;
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| 64 | int i, j;
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| 65 |
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| 66 | bn_check_top(a);
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| 67 | w &= BN_MASK2;
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| 68 |
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| 69 | if (!w)
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| 70 | /* actually this an error (division by zero) */
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| 71 | return (BN_ULONG)-1;
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| 72 | if (a->top == 0)
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| 73 | return 0;
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| 74 |
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| 75 | /* normalize input (so bn_div_words doesn't complain) */
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| 76 | j = BN_BITS2 - BN_num_bits_word(w);
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| 77 | w <<= j;
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| 78 | if (!BN_lshift(a, a, j))
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| 79 | return (BN_ULONG)-1;
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| 80 |
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| 81 | for (i = a->top - 1; i >= 0; i--) {
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| 82 | BN_ULONG l, d;
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| 83 |
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| 84 | l = a->d[i];
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| 85 | d = bn_div_words(ret, l, w);
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| 86 | ret = (l - ((d * w) & BN_MASK2)) & BN_MASK2;
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| 87 | a->d[i] = d;
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| 88 | }
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| 89 | if ((a->top > 0) && (a->d[a->top - 1] == 0))
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| 90 | a->top--;
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| 91 | ret >>= j;
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| 92 | if (!a->top)
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| 93 | a->neg = 0; /* don't allow negative zero */
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| 94 | bn_check_top(a);
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| 95 | return (ret);
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| 96 | }
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| 97 |
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| 98 | int BN_add_word(BIGNUM *a, BN_ULONG w)
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| 99 | {
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| 100 | BN_ULONG l;
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| 101 | int i;
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| 102 |
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| 103 | bn_check_top(a);
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| 104 | w &= BN_MASK2;
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| 105 |
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| 106 | /* degenerate case: w is zero */
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| 107 | if (!w)
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| 108 | return 1;
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| 109 | /* degenerate case: a is zero */
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| 110 | if (BN_is_zero(a))
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| 111 | return BN_set_word(a, w);
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| 112 | /* handle 'a' when negative */
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| 113 | if (a->neg) {
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| 114 | a->neg = 0;
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| 115 | i = BN_sub_word(a, w);
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| 116 | if (!BN_is_zero(a))
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| 117 | a->neg = !(a->neg);
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| 118 | return (i);
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| 119 | }
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| 120 | for (i = 0; w != 0 && i < a->top; i++) {
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| 121 | a->d[i] = l = (a->d[i] + w) & BN_MASK2;
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| 122 | w = (w > l) ? 1 : 0;
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| 123 | }
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| 124 | if (w && i == a->top) {
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| 125 | if (bn_wexpand(a, a->top + 1) == NULL)
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| 126 | return 0;
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| 127 | a->top++;
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| 128 | a->d[i] = w;
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| 129 | }
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| 130 | bn_check_top(a);
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| 131 | return (1);
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| 132 | }
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| 133 |
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| 134 | int BN_sub_word(BIGNUM *a, BN_ULONG w)
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| 135 | {
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| 136 | int i;
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| 137 |
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| 138 | bn_check_top(a);
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| 139 | w &= BN_MASK2;
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| 140 |
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| 141 | /* degenerate case: w is zero */
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| 142 | if (!w)
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| 143 | return 1;
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| 144 | /* degenerate case: a is zero */
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| 145 | if (BN_is_zero(a)) {
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| 146 | i = BN_set_word(a, w);
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| 147 | if (i != 0)
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| 148 | BN_set_negative(a, 1);
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| 149 | return i;
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| 150 | }
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| 151 | /* handle 'a' when negative */
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| 152 | if (a->neg) {
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| 153 | a->neg = 0;
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| 154 | i = BN_add_word(a, w);
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| 155 | a->neg = 1;
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| 156 | return (i);
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| 157 | }
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| 158 |
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| 159 | if ((a->top == 1) && (a->d[0] < w)) {
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| 160 | a->d[0] = w - a->d[0];
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| 161 | a->neg = 1;
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| 162 | return (1);
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| 163 | }
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| 164 | i = 0;
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| 165 | for (;;) {
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| 166 | if (a->d[i] >= w) {
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| 167 | a->d[i] -= w;
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| 168 | break;
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| 169 | } else {
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| 170 | a->d[i] = (a->d[i] - w) & BN_MASK2;
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| 171 | i++;
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| 172 | w = 1;
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| 173 | }
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| 174 | }
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| 175 | if ((a->d[i] == 0) && (i == (a->top - 1)))
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| 176 | a->top--;
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| 177 | bn_check_top(a);
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| 178 | return (1);
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| 179 | }
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| 180 |
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| 181 | int BN_mul_word(BIGNUM *a, BN_ULONG w)
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| 182 | {
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| 183 | BN_ULONG ll;
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| 184 |
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| 185 | bn_check_top(a);
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| 186 | w &= BN_MASK2;
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| 187 | if (a->top) {
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| 188 | if (w == 0)
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| 189 | BN_zero(a);
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| 190 | else {
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| 191 | ll = bn_mul_words(a->d, a->d, a->top, w);
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| 192 | if (ll) {
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| 193 | if (bn_wexpand(a, a->top + 1) == NULL)
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| 194 | return (0);
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| 195 | a->d[a->top++] = ll;
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| 196 | }
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| 197 | }
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| 198 | }
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| 199 | bn_check_top(a);
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| 200 | return (1);
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| 201 | }
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