crypto/openssl/crypto/bn/bn_sqr.c

   1 /* crypto/bn/bn_sqr.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 /* r must not be a */
  64 /*
  65  * I've just gone over this and it is now %20 faster on x86 - eay - 27 Jun 96
  66  */
  67 int BN_sqr(BIGNUM *r, const BIGNUM *a, BN_CTX *ctx)
  68 {
  69     int max, al;
  70     int ret = 0;
  71     BIGNUM *tmp, *rr;
  72
  73 #ifdef BN_COUNT
  74     fprintf(stderr, "BN_sqr %d * %d\n", a->top, a->top);
  75 #endif
  76     bn_check_top(a);
  77
  78     al = a->top;
  79     if (al <= 0) {
  80         r->top = 0;
  81         r->neg = 0;
  82         return 1;
  83     }
  84
  85     BN_CTX_start(ctx);
  86     rr = (a != r) ? r : BN_CTX_get(ctx);
  87     tmp = BN_CTX_get(ctx);
  88     if (!rr || !tmp)
  89         goto err;
  90
  91     max = 2 * al;               /* Non-zero (from above) */
  92     if (bn_wexpand(rr, max) == NULL)
  93         goto err;
  94
  95     if (al == 4) {
  96 #ifndef BN_SQR_COMBA
  97         BN_ULONG t[8];
  98         bn_sqr_normal(rr->d, a->d, 4, t);
  99 #else
 100         bn_sqr_comba4(rr->d, a->d);
 101 #endif
 102     } else if (al == 8) {
 103 #ifndef BN_SQR_COMBA
 104         BN_ULONG t[16];
 105         bn_sqr_normal(rr->d, a->d, 8, t);
 106 #else
 107         bn_sqr_comba8(rr->d, a->d);
 108 #endif
 109     } else {
 110 #if defined(BN_RECURSION)
 111         if (al < BN_SQR_RECURSIVE_SIZE_NORMAL) {
 112             BN_ULONG t[BN_SQR_RECURSIVE_SIZE_NORMAL * 2];
 113             bn_sqr_normal(rr->d, a->d, al, t);
 114         } else {
 115             int j, k;
 116
 117             j = BN_num_bits_word((BN_ULONG)al);
 118             j = 1 << (j - 1);
 119             k = j + j;
 120             if (al == j) {
 121                 if (bn_wexpand(tmp, k * 2) == NULL)
 122                     goto err;
 123                 bn_sqr_recursive(rr->d, a->d, al, tmp->d);
 124             } else {
 125                 if (bn_wexpand(tmp, max) == NULL)
 126                     goto err;
 127                 bn_sqr_normal(rr->d, a->d, al, tmp->d);
 128             }
 129         }
 130 #else
 131         if (bn_wexpand(tmp, max) == NULL)
 132             goto err;
 133         bn_sqr_normal(rr->d, a->d, al, tmp->d);
 134 #endif
 135     }
 136
 137     rr->neg = 0;
 138     /*
 139      * If the most-significant half of the top word of 'a' is zero, then the
 140      * square of 'a' will max-1 words.
 141      */
 142     if (a->d[al - 1] == (a->d[al - 1] & BN_MASK2l))
 143         rr->top = max - 1;
 144     else
 145         rr->top = max;
 146     if (rr != r)
 147         BN_copy(r, rr);
 148     ret = 1;
 149  err:
 150     bn_check_top(rr);
 151     bn_check_top(tmp);
 152     BN_CTX_end(ctx);
 153     return (ret);
 154 }
 155
 156 /* tmp must have 2*n words */
 157 void bn_sqr_normal(BN_ULONG *r, const BN_ULONG *a, int n, BN_ULONG *tmp)
 158 {
 159     int i, j, max;
 160     const BN_ULONG *ap;
 161     BN_ULONG *rp;
 162
 163     max = n * 2;
 164     ap = a;
 165     rp = r;
 166     rp[0] = rp[max - 1] = 0;
 167     rp++;
 168     j = n;
 169
 170     if (--j > 0) {
 171         ap++;
 172         rp[j] = bn_mul_words(rp, ap, j, ap[-1]);
 173         rp += 2;
 174     }
 175
 176     for (i = n - 2; i > 0; i--) {
 177         j--;
 178         ap++;
 179         rp[j] = bn_mul_add_words(rp, ap, j, ap[-1]);
 180         rp += 2;
 181     }
 182
 183     bn_add_words(r, r, r, max);
 184
 185     /* There will not be a carry */
 186
 187     bn_sqr_words(tmp, a, n);
 188
 189     bn_add_words(r, r, tmp, max);
 190 }
 191
 192 #ifdef BN_RECURSION
 193 /*-
 194  * r is 2*n words in size,
 195  * a and b are both n words in size.    (There's not actually a 'b' here ...)
 196  * n must be a power of 2.
 197  * We multiply and return the result.
 198  * t must be 2*n words in size
 199  * We calculate
 200  * a[0]*b[0]
 201  * a[0]*b[0]+a[1]*b[1]+(a[0]-a[1])*(b[1]-b[0])
 202  * a[1]*b[1]
 203  */
 204 void bn_sqr_recursive(BN_ULONG *r, const BN_ULONG *a, int n2, BN_ULONG *t)
 205 {
 206     int n = n2 / 2;
 207     int zero, c1;
 208     BN_ULONG ln, lo, *p;
 209
 210 # ifdef BN_COUNT
 211     fprintf(stderr, " bn_sqr_recursive %d * %d\n", n2, n2);
 212 # endif
 213     if (n2 == 4) {
 214 # ifndef BN_SQR_COMBA
 215         bn_sqr_normal(r, a, 4, t);
 216 # else
 217         bn_sqr_comba4(r, a);
 218 # endif
 219         return;
 220     } else if (n2 == 8) {
 221 # ifndef BN_SQR_COMBA
 222         bn_sqr_normal(r, a, 8, t);
 223 # else
 224         bn_sqr_comba8(r, a);
 225 # endif
 226         return;
 227     }
 228     if (n2 < BN_SQR_RECURSIVE_SIZE_NORMAL) {
 229         bn_sqr_normal(r, a, n2, t);
 230         return;
 231     }
 232     /* r=(a[0]-a[1])*(a[1]-a[0]) */
 233     c1 = bn_cmp_words(a, &(a[n]), n);
 234     zero = 0;
 235     if (c1 > 0)
 236         bn_sub_words(t, a, &(a[n]), n);
 237     else if (c1 < 0)
 238         bn_sub_words(t, &(a[n]), a, n);
 239     else
 240         zero = 1;
 241
 242     /* The result will always be negative unless it is zero */
 243     p = &(t[n2 * 2]);
 244
 245     if (!zero)
 246         bn_sqr_recursive(&(t[n2]), t, n, p);
 247     else
 248         memset(&(t[n2]), 0, n2 * sizeof(BN_ULONG));
 249     bn_sqr_recursive(r, a, n, p);
 250     bn_sqr_recursive(&(r[n2]), &(a[n]), n, p);
 251
 252     /*-
 253      * t[32] holds (a[0]-a[1])*(a[1]-a[0]), it is negative or zero
 254      * r[10] holds (a[0]*b[0])
 255      * r[32] holds (b[1]*b[1])
 256      */
 257
 258     c1 = (int)(bn_add_words(t, r, &(r[n2]), n2));
 259
 260     /* t[32] is negative */
 261     c1 -= (int)(bn_sub_words(&(t[n2]), t, &(t[n2]), n2));
 262
 263     /*-
 264      * t[32] holds (a[0]-a[1])*(a[1]-a[0])+(a[0]*a[0])+(a[1]*a[1])
 265      * r[10] holds (a[0]*a[0])
 266      * r[32] holds (a[1]*a[1])
 267      * c1 holds the carry bits
 268      */
 269     c1 += (int)(bn_add_words(&(r[n]), &(r[n]), &(t[n2]), n2));
 270     if (c1) {
 271         p = &(r[n + n2]);
 272         lo = *p;
 273         ln = (lo + c1) & BN_MASK2;
 274         *p = ln;
 275
 276         /*
 277          * The overflow will stop before we over write words we should not
 278          * overwrite
 279          */
 280         if (ln < (BN_ULONG)c1) {
 281             do {
 282                 p++;
 283                 lo = *p;
 284                 ln = (lo + 1) & BN_MASK2;
 285                 *p = ln;
 286             } while (ln == 0);
 287         }
 288     }
 289 }
 290 #endif