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1/* crypto/bn/bn_sub.c */
2/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
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. */
64void bn_qsub(r, a, b)
65BIGNUM *r;
66BIGNUM *a;
67BIGNUM *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);
90 t1=(t1-t2-1)&BN_MASK2;
91 }
92 else
93 {
94 carry=(t1 < t2);
95 t1=(t1-t2)&BN_MASK2;
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 }
113#if 0
114 memcpy(rp,ap,sizeof(*rp)*(max-i));
115#else
116 for (; i<max; i++)
117 *(rp++)= *(ap++);
118#endif
119
120 r->top=max;
121 bn_fix_top(r);
122 }
123
124int BN_sub(r, a, b)
125BIGNUM *r;
126BIGNUM *a;
127BIGNUM *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 {
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)
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;
167 if (bn_wexpand(r,max) == NULL) return(0);
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
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