bn_add.c 6.7 KB

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  1. /* crypto/bn/bn_add.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. #include <stdio.h>
  59. #include "cryptlib.h"
  60. #include "bn_lcl.h"
  61. /* r can == a or b */
  62. int BN_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
  63. {
  64. const BIGNUM *tmp;
  65. int a_neg = a->neg, ret;
  66. bn_check_top(a);
  67. bn_check_top(b);
  68. /* a + b a+b
  69. * a + -b a-b
  70. * -a + b b-a
  71. * -a + -b -(a+b)
  72. */
  73. if (a_neg ^ b->neg)
  74. {
  75. /* only one is negative */
  76. if (a_neg)
  77. { tmp=a; a=b; b=tmp; }
  78. /* we are now a - b */
  79. if (BN_ucmp(a,b) < 0)
  80. {
  81. if (!BN_usub(r,b,a)) return(0);
  82. r->neg=1;
  83. }
  84. else
  85. {
  86. if (!BN_usub(r,a,b)) return(0);
  87. r->neg=0;
  88. }
  89. return(1);
  90. }
  91. ret = BN_uadd(r,a,b);
  92. r->neg = a_neg;
  93. bn_check_top(r);
  94. return ret;
  95. }
  96. /* unsigned add of b to a */
  97. int BN_uadd(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
  98. {
  99. int max,min,dif;
  100. BN_ULONG *ap,*bp,*rp,carry,t1,t2;
  101. const BIGNUM *tmp;
  102. bn_check_top(a);
  103. bn_check_top(b);
  104. if (a->top < b->top)
  105. { tmp=a; a=b; b=tmp; }
  106. max = a->top;
  107. min = b->top;
  108. dif = max - min;
  109. if (bn_wexpand(r,max+1) == NULL)
  110. return 0;
  111. r->top=max;
  112. ap=a->d;
  113. bp=b->d;
  114. rp=r->d;
  115. carry=bn_add_words(rp,ap,bp,min);
  116. rp+=min;
  117. ap+=min;
  118. bp+=min;
  119. if (carry)
  120. {
  121. while (dif)
  122. {
  123. dif--;
  124. t1 = *(ap++);
  125. t2 = (t1+1) & BN_MASK2;
  126. *(rp++) = t2;
  127. if (t2)
  128. {
  129. carry=0;
  130. break;
  131. }
  132. }
  133. if (carry)
  134. {
  135. /* carry != 0 => dif == 0 */
  136. *rp = 1;
  137. r->top++;
  138. }
  139. }
  140. if (dif && rp != ap)
  141. while (dif--)
  142. /* copy remaining words if ap != rp */
  143. *(rp++) = *(ap++);
  144. r->neg = 0;
  145. bn_check_top(r);
  146. return 1;
  147. }
  148. /* unsigned subtraction of b from a, a must be larger than b. */
  149. int BN_usub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
  150. {
  151. int max,min,dif;
  152. register BN_ULONG t1,t2,*ap,*bp,*rp;
  153. int i,carry;
  154. #if defined(IRIX_CC_BUG) && !defined(LINT)
  155. int dummy;
  156. #endif
  157. bn_check_top(a);
  158. bn_check_top(b);
  159. max = a->top;
  160. min = b->top;
  161. dif = max - min;
  162. if (dif < 0) /* hmm... should not be happening */
  163. {
  164. BNerr(BN_F_BN_USUB,BN_R_ARG2_LT_ARG3);
  165. return(0);
  166. }
  167. if (bn_wexpand(r,max) == NULL) return(0);
  168. ap=a->d;
  169. bp=b->d;
  170. rp=r->d;
  171. #if 1
  172. carry=0;
  173. for (i = min; i != 0; i--)
  174. {
  175. t1= *(ap++);
  176. t2= *(bp++);
  177. if (carry)
  178. {
  179. carry=(t1 <= t2);
  180. t1=(t1-t2-1)&BN_MASK2;
  181. }
  182. else
  183. {
  184. carry=(t1 < t2);
  185. t1=(t1-t2)&BN_MASK2;
  186. }
  187. #if defined(IRIX_CC_BUG) && !defined(LINT)
  188. dummy=t1;
  189. #endif
  190. *(rp++)=t1&BN_MASK2;
  191. }
  192. #else
  193. carry=bn_sub_words(rp,ap,bp,min);
  194. ap+=min;
  195. bp+=min;
  196. rp+=min;
  197. #endif
  198. if (carry) /* subtracted */
  199. {
  200. if (!dif)
  201. /* error: a < b */
  202. return 0;
  203. while (dif)
  204. {
  205. dif--;
  206. t1 = *(ap++);
  207. t2 = (t1-1)&BN_MASK2;
  208. *(rp++) = t2;
  209. if (t1)
  210. break;
  211. }
  212. }
  213. #if 0
  214. memcpy(rp,ap,sizeof(*rp)*(max-i));
  215. #else
  216. if (rp != ap)
  217. {
  218. for (;;)
  219. {
  220. if (!dif--) break;
  221. rp[0]=ap[0];
  222. if (!dif--) break;
  223. rp[1]=ap[1];
  224. if (!dif--) break;
  225. rp[2]=ap[2];
  226. if (!dif--) break;
  227. rp[3]=ap[3];
  228. rp+=4;
  229. ap+=4;
  230. }
  231. }
  232. #endif
  233. r->top=max;
  234. r->neg=0;
  235. bn_correct_top(r);
  236. return(1);
  237. }
  238. int BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b)
  239. {
  240. int max;
  241. int add=0,neg=0;
  242. const BIGNUM *tmp;
  243. bn_check_top(a);
  244. bn_check_top(b);
  245. /* a - b a-b
  246. * a - -b a+b
  247. * -a - b -(a+b)
  248. * -a - -b b-a
  249. */
  250. if (a->neg)
  251. {
  252. if (b->neg)
  253. { tmp=a; a=b; b=tmp; }
  254. else
  255. { add=1; neg=1; }
  256. }
  257. else
  258. {
  259. if (b->neg) { add=1; neg=0; }
  260. }
  261. if (add)
  262. {
  263. if (!BN_uadd(r,a,b)) return(0);
  264. r->neg=neg;
  265. return(1);
  266. }
  267. /* We are actually doing a - b :-) */
  268. max=(a->top > b->top)?a->top:b->top;
  269. if (bn_wexpand(r,max) == NULL) return(0);
  270. if (BN_ucmp(a,b) < 0)
  271. {
  272. if (!BN_usub(r,b,a)) return(0);
  273. r->neg=1;
  274. }
  275. else
  276. {
  277. if (!BN_usub(r,a,b)) return(0);
  278. r->neg=0;
  279. }
  280. bn_check_top(r);
  281. return(1);
  282. }