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d02b48c6 | 1 | /* crypto/bn/bn_sub.c */ |
58964a49 | 2 | /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com) |
d02b48c6 RE |
3 | * All rights reserved. |
4 | * | |
5 | * This package is an SSL implementation written | |
6 | * by Eric Young (eay@cryptsoft.com). | |
7 | * The implementation was written so as to conform with Netscapes SSL. | |
8 | * | |
9 | * This library is free for commercial and non-commercial use as long as | |
10 | * the following conditions are aheared to. The following conditions | |
11 | * apply to all code found in this distribution, be it the RC4, RSA, | |
12 | * lhash, DES, etc., code; not just the SSL code. The SSL documentation | |
13 | * included with this distribution is covered by the same copyright terms | |
14 | * except that the holder is Tim Hudson (tjh@cryptsoft.com). | |
15 | * | |
16 | * Copyright remains Eric Young's, and as such any Copyright notices in | |
17 | * the code are not to be removed. | |
18 | * If this package is used in a product, Eric Young should be given attribution | |
19 | * as the author of the parts of the library used. | |
20 | * This can be in the form of a textual message at program startup or | |
21 | * in documentation (online or textual) provided with the package. | |
22 | * | |
23 | * Redistribution and use in source and binary forms, with or without | |
24 | * modification, are permitted provided that the following conditions | |
25 | * are met: | |
26 | * 1. Redistributions of source code must retain the copyright | |
27 | * notice, this list of conditions and the following disclaimer. | |
28 | * 2. Redistributions in binary form must reproduce the above copyright | |
29 | * notice, this list of conditions and the following disclaimer in the | |
30 | * documentation and/or other materials provided with the distribution. | |
31 | * 3. All advertising materials mentioning features or use of this software | |
32 | * must display the following acknowledgement: | |
33 | * "This product includes cryptographic software written by | |
34 | * Eric Young (eay@cryptsoft.com)" | |
35 | * The word 'cryptographic' can be left out if the rouines from the library | |
36 | * being used are not cryptographic related :-). | |
37 | * 4. If you include any Windows specific code (or a derivative thereof) from | |
38 | * the apps directory (application code) you must include an acknowledgement: | |
39 | * "This product includes software written by Tim Hudson (tjh@cryptsoft.com)" | |
40 | * | |
41 | * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND | |
42 | * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE | |
43 | * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE | |
44 | * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE | |
45 | * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL | |
46 | * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS | |
47 | * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) | |
48 | * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | |
49 | * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | |
50 | * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | |
51 | * SUCH DAMAGE. | |
52 | * | |
53 | * The licence and distribution terms for any publically available version or | |
54 | * derivative of this code cannot be changed. i.e. this code cannot simply be | |
55 | * copied and put under another distribution licence | |
56 | * [including the GNU Public Licence.] | |
57 | */ | |
58 | ||
59 | #include <stdio.h> | |
60 | #include "cryptlib.h" | |
61 | #include "bn_lcl.h" | |
62 | ||
63 | /* unsigned subtraction of b from a, a must be larger than b. */ | |
64 | void bn_qsub(r, a, b) | |
65 | BIGNUM *r; | |
66 | BIGNUM *a; | |
67 | BIGNUM *b; | |
68 | { | |
69 | int max,min; | |
70 | register BN_ULONG t1,t2,*ap,*bp,*rp; | |
71 | int i,carry; | |
72 | #if defined(IRIX_CC_BUG) && !defined(LINT) | |
73 | int dummy; | |
74 | #endif | |
75 | ||
76 | max=a->top; | |
77 | min=b->top; | |
78 | ap=a->d; | |
79 | bp=b->d; | |
80 | rp=r->d; | |
81 | ||
82 | carry=0; | |
83 | for (i=0; i<min; i++) | |
84 | { | |
85 | t1= *(ap++); | |
86 | t2= *(bp++); | |
87 | if (carry) | |
88 | { | |
89 | carry=(t1 <= t2); | |
58964a49 | 90 | t1=(t1-t2-1)&BN_MASK2; |
d02b48c6 RE |
91 | } |
92 | else | |
93 | { | |
94 | carry=(t1 < t2); | |
58964a49 | 95 | t1=(t1-t2)&BN_MASK2; |
d02b48c6 RE |
96 | } |
97 | #if defined(IRIX_CC_BUG) && !defined(LINT) | |
98 | dummy=t1; | |
99 | #endif | |
100 | *(rp++)=t1&BN_MASK2; | |
101 | } | |
102 | if (carry) /* subtracted */ | |
103 | { | |
104 | while (i < max) | |
105 | { | |
106 | i++; | |
107 | t1= *(ap++); | |
108 | t2=(t1-1)&BN_MASK2; | |
109 | *(rp++)=t2; | |
110 | if (t1 > t2) break; | |
111 | } | |
112 | } | |
58964a49 | 113 | #if 0 |
d02b48c6 | 114 | memcpy(rp,ap,sizeof(*rp)*(max-i)); |
58964a49 RE |
115 | #else |
116 | for (; i<max; i++) | |
117 | *(rp++)= *(ap++); | |
118 | #endif | |
d02b48c6 RE |
119 | |
120 | r->top=max; | |
121 | bn_fix_top(r); | |
122 | } | |
123 | ||
124 | int BN_sub(r, a, b) | |
125 | BIGNUM *r; | |
126 | BIGNUM *a; | |
127 | BIGNUM *b; | |
128 | { | |
129 | int max,i; | |
130 | int add=0,neg=0; | |
131 | BIGNUM *tmp; | |
132 | ||
133 | /* a - b a-b | |
134 | * a - -b a+b | |
135 | * -a - b -(a+b) | |
136 | * -a - -b b-a | |
137 | */ | |
138 | if (a->neg) | |
139 | { | |
140 | if (b->neg) | |
141 | { tmp=a; a=b; b=tmp; } | |
142 | else | |
143 | { add=1; neg=1; } | |
144 | } | |
145 | else | |
146 | { | |
147 | if (b->neg) { add=1; neg=0; } | |
148 | } | |
149 | ||
150 | if (add) | |
151 | { | |
58964a49 RE |
152 | /* As a fast max size, do a a->top | b->top */ |
153 | i=(a->top | b->top)+1; | |
154 | if (bn_wexpand(r,i) == NULL) | |
d02b48c6 RE |
155 | return(0); |
156 | if (i) | |
157 | bn_qadd(r,a,b); | |
158 | else | |
159 | bn_qadd(r,b,a); | |
160 | r->neg=neg; | |
161 | return(1); | |
162 | } | |
163 | ||
164 | /* We are actually doing a - b :-) */ | |
165 | ||
166 | max=(a->top > b->top)?a->top:b->top; | |
58964a49 | 167 | if (bn_wexpand(r,max) == NULL) return(0); |
d02b48c6 RE |
168 | if (BN_ucmp(a,b) < 0) |
169 | { | |
170 | bn_qsub(r,b,a); | |
171 | r->neg=1; | |
172 | } | |
173 | else | |
174 | { | |
175 | bn_qsub(r,a,b); | |
176 | r->neg=0; | |
177 | } | |
178 | return(1); | |
179 | } | |
180 |