Mercurial > dropbear

annotate libtommath/bn_s_mp_karatsuba_mul.c @ 1788:1fc0012b9c38

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Fix handling of replies to global requests (#112) The current code assumes that all global requests want / need a reply. This isn't always true and the request itself indicates if it wants a reply or not. It causes a specific problem with [email protected] messages. These are sent by OpenSSH after authentication to inform the client of potential other host keys for the host. This can be used to add a new type of host key or to rotate host keys. The initial information message from the server is sent as a global request, but with want_reply set to false. This means that the server doesn't expect an answer to this message. Instead the client needs to send a prove request as a reply if it wants to receive proof of ownership for the host keys. The bug doesn't cause any current problems with due to how OpenSSH treats receiving the failure message. It instead treats it as a keepalive message and further ignores it. Arguably this is a protocol violation though of Dropbear and it is only accidental that it doesn't cause a problem with OpenSSH. The bug was found when adding host keys support to libssh, which is more strict protocol wise and treats the unexpected failure message an error, also see https://gitlab.com/libssh/libssh-mirror/-/merge_requests/145 for more information. The fix here is to honor the want_reply flag in the global request and to only send a reply if the other side expects a reply.
author Dirkjan Bussink <d.bussink@gmail.com>
date Thu, 10 Dec 2020 16:13:13 +0100
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"
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2 #ifdef BN_S_MP_KARATSUBA_MUL_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 /* c = |a| * |b| using Karatsuba Multiplication using
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7 * three half size multiplications
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8 *
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9 * Let B represent the radix [e.g. 2**MP_DIGIT_BIT] and
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10 * let n represent half of the number of digits in
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11 * the min(a,b)
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12 *
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13 * a = a1 * B**n + a0
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14 * b = b1 * B**n + b0
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15 *
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16 * Then, a * b =>
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17 a1b1 * B**2n + ((a1 + a0)(b1 + b0) - (a0b0 + a1b1)) * B + a0b0
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18 *
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19 * Note that a1b1 and a0b0 are used twice and only need to be
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20 * computed once. So in total three half size (half # of
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21 * digit) multiplications are performed, a0b0, a1b1 and
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22 * (a1+b1)(a0+b0)
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23 *
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24 * Note that a multiplication of half the digits requires
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25 * 1/4th the number of single precision multiplications so in
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26 * total after one call 25% of the single precision multiplications
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27 * are saved. Note also that the call to mp_mul can end up back
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28 * in this function if the a0, a1, b0, or b1 are above the threshold.
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29 * This is known as divide-and-conquer and leads to the famous
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30 * O(N**lg(3)) or O(N**1.584) work which is asymptopically lower than
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31 * the standard O(N**2) that the baseline/comba methods use.
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32 * Generally though the overhead of this method doesn't pay off
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33 * until a certain size (N ~ 80) is reached.
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34 */
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35 mp_err s_mp_karatsuba_mul(const mp_int *a, const mp_int *b, mp_int *c)
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36 {
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37 mp_int x0, x1, y0, y1, t1, x0y0, x1y1;
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38 int B;
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39 mp_err err = MP_MEM; /* default the return code to an error */
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40
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41 /* min # of digits */
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42 B = MP_MIN(a->used, b->used);
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43
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44 /* now divide in two */
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45 B = B >> 1;
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46
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47 /* init copy all the temps */
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48 if (mp_init_size(&x0, B) != MP_OKAY) {
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49 goto LBL_ERR;
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50 }
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51 if (mp_init_size(&x1, a->used - B) != MP_OKAY) {
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52 goto X0;
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53 }
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54 if (mp_init_size(&y0, B) != MP_OKAY) {
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55 goto X1;
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56 }
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57 if (mp_init_size(&y1, b->used - B) != MP_OKAY) {
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58 goto Y0;
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59 }
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60
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61 /* init temps */
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62 if (mp_init_size(&t1, B * 2) != MP_OKAY) {
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63 goto Y1;
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64 }
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65 if (mp_init_size(&x0y0, B * 2) != MP_OKAY) {
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66 goto T1;
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67 }
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68 if (mp_init_size(&x1y1, B * 2) != MP_OKAY) {
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69 goto X0Y0;
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70 }
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71
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72 /* now shift the digits */
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73 x0.used = y0.used = B;
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74 x1.used = a->used - B;
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75 y1.used = b->used - B;
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76
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77 {
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78 int x;
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79 mp_digit *tmpa, *tmpb, *tmpx, *tmpy;
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80
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81 /* we copy the digits directly instead of using higher level functions
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82 * since we also need to shift the digits
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83 */
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84 tmpa = a->dp;
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85 tmpb = b->dp;
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86
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87 tmpx = x0.dp;
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88 tmpy = y0.dp;
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89 for (x = 0; x < B; x++) {
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90 *tmpx++ = *tmpa++;
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91 *tmpy++ = *tmpb++;
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92 }
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93
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94 tmpx = x1.dp;
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95 for (x = B; x < a->used; x++) {
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96 *tmpx++ = *tmpa++;
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97 }
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98
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99 tmpy = y1.dp;
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100 for (x = B; x < b->used; x++) {
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101 *tmpy++ = *tmpb++;
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102 }
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103 }
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104
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105 /* only need to clamp the lower words since by definition the
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106 * upper words x1/y1 must have a known number of digits
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107 */
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108 mp_clamp(&x0);
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109 mp_clamp(&y0);
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110
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111 /* now calc the products x0y0 and x1y1 */
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112 /* after this x0 is no longer required, free temp [x0==t2]! */
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113 if (mp_mul(&x0, &y0, &x0y0) != MP_OKAY) {
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114 goto X1Y1; /* x0y0 = x0*y0 */
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115 }
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116 if (mp_mul(&x1, &y1, &x1y1) != MP_OKAY) {
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117 goto X1Y1; /* x1y1 = x1*y1 */
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118 }
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119
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120 /* now calc x1+x0 and y1+y0 */
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121 if (s_mp_add(&x1, &x0, &t1) != MP_OKAY) {
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122 goto X1Y1; /* t1 = x1 - x0 */
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123 }
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
124 if (s_mp_add(&y1, &y0, &x0) != MP_OKAY) {
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
125 goto X1Y1; /* t2 = y1 - y0 */
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
126 }
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
127 if (mp_mul(&t1, &x0, &t1) != MP_OKAY) {
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
128 goto X1Y1; /* t1 = (x1 + x0) * (y1 + y0) */
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
129 }
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
130
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
131 /* add x0y0 */
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
132 if (mp_add(&x0y0, &x1y1, &x0) != MP_OKAY) {
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
133 goto X1Y1; /* t2 = x0y0 + x1y1 */
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
134 }
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
135 if (s_mp_sub(&t1, &x0, &t1) != MP_OKAY) {
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
136 goto X1Y1; /* t1 = (x1+x0)*(y1+y0) - (x1y1 + x0y0) */
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
137 }
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 /* shift by B */
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
140 if (mp_lshd(&t1, B) != MP_OKAY) {
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
141 goto X1Y1; /* t1 = (x0y0 + x1y1 - (x1-x0)*(y1-y0))<<B */
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 if (mp_lshd(&x1y1, B * 2) != MP_OKAY) {
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
144 goto X1Y1; /* x1y1 = x1y1 << 2*B */
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
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
147 if (mp_add(&x0y0, &t1, &t1) != MP_OKAY) {
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
148 goto X1Y1; /* t1 = x0y0 + t1 */
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
149 }
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
150 if (mp_add(&t1, &x1y1, c) != MP_OKAY) {
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
151 goto X1Y1; /* t1 = x0y0 + t1 + x1y1 */
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
152 }
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
153
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
154 /* Algorithm succeeded set the return code to MP_OKAY */
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
155 err = MP_OKAY;
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
156
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
157 X1Y1:
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
158 mp_clear(&x1y1);
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
159 X0Y0:
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
160 mp_clear(&x0y0);
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
161 T1:
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
162 mp_clear(&t1);
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
163 Y1:
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
164 mp_clear(&y1);
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
165 Y0:
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
166 mp_clear(&y0);
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
167 X1:
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
168 mp_clear(&x1);
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
169 X0:
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
170 mp_clear(&x0);
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
171 LBL_ERR:
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
172 return err;
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
173 }
1051e4eea25a Update LibTomMath to 1.2.0 (#84)
Steffen Jaeckel <s@jaeckel.eu>
parents:
diff changeset
174 #endif