crypto/bn/bn_div.c

   1 /* crypto/bn/bn_div.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 /* The old slow way */
  64 #if 0
  65 int BN_div(dv, rem, m, d,ctx)
  66 BIGNUM *dv;
  67 BIGNUM *rem;
  68 BIGNUM *m;
  69 BIGNUM *d;
  70 BN_CTX *ctx;
  71         {
  72         int i,nm,nd;
  73         BIGNUM *D;
  74
  75         bn_check_top(m);
  76         bn_check_top(d);
  77         if (BN_is_zero(d))
  78                 {
  79                 BNerr(BN_F_BN_DIV,BN_R_DIV_BY_ZERO);
  80                 return(0);
  81                 }
  82
  83         if (BN_ucmp(m,d) < 0)
  84                 {
  85                 if (rem != NULL)
  86                         { if (BN_copy(rem,m) == NULL) return(0); }
  87                 if (dv != NULL) BN_zero(dv);
  88                 return(1);
  89                 }
  90
  91         D= &(ctx->bn[ctx->tos]);
  92         if (dv == NULL) dv= &(ctx->bn[ctx->tos+1]);
  93         if (rem == NULL) rem= &(ctx->bn[ctx->tos+2]);
  94
  95         nd=BN_num_bits(d);
  96         nm=BN_num_bits(m);
  97         if (BN_copy(D,d) == NULL) return(0);
  98         if (BN_copy(rem,m) == NULL) return(0);
  99
 100         /* The next 2 are needed so we can do a dv->d[0]|=1 later
 101          * since BN_lshift1 will only work once there is a value :-) */
 102         BN_zero(dv);
 103         bn_wexpand(dv,1);
 104         dv->top=1;
 105
 106         if (!BN_lshift(D,D,nm-nd)) return(0);
 107         for (i=nm-nd; i>=0; i--)
 108                 {
 109                 if (!BN_lshift1(dv,dv)) return(0);
 110                 if (BN_ucmp(rem,D) >= 0)
 111                         {
 112                         dv->d[0]|=1;
 113                         if (!BN_usub(rem,rem,D)) return(0);
 114                         }
 115 /* CAN IMPROVE (and have now :=) */
 116                 if (!BN_rshift1(D,D)) return(0);
 117                 }
 118         rem->neg=BN_is_zero(rem)?0:m->neg;
 119         dv->neg=m->neg^d->neg;
 120         return(1);
 121         }
 122
 123 #else
 124
 125 int BN_div(dv, rm, num, divisor,ctx)
 126 BIGNUM *dv;
 127 BIGNUM *rm;
 128 BIGNUM *num;
 129 BIGNUM *divisor;
 130 BN_CTX *ctx;
 131         {
 132         int norm_shift,i,j,loop;
 133         BIGNUM *tmp,wnum,*snum,*sdiv,*res;
 134         BN_ULONG *resp,*wnump;
 135         BN_ULONG d0,d1;
 136         int num_n,div_n;
 137
 138         bn_check_top(num);
 139         bn_check_top(divisor);
 140
 141         if (BN_is_zero(divisor))
 142                 {
 143                 BNerr(BN_F_BN_DIV,BN_R_DIV_BY_ZERO);
 144                 return(0);
 145                 }
 146
 147         if (BN_ucmp(num,divisor) < 0)
 148                 {
 149                 if (rm != NULL)
 150                         { if (BN_copy(rm,num) == NULL) return(0); }
 151                 if (dv != NULL) BN_zero(dv);
 152                 return(1);
 153                 }
 154
 155         tmp= &(ctx->bn[ctx->tos]);
 156         tmp->neg=0;
 157         snum= &(ctx->bn[ctx->tos+1]);
 158         sdiv= &(ctx->bn[ctx->tos+2]);
 159         if (dv == NULL)
 160                 res= &(ctx->bn[ctx->tos+3]);
 161         else    res=dv;
 162
 163         /* First we normalise the numbers */
 164         norm_shift=BN_BITS2-((BN_num_bits(divisor))%BN_BITS2);
 165         BN_lshift(sdiv,divisor,norm_shift);
 166         sdiv->neg=0;
 167         norm_shift+=BN_BITS2;
 168         BN_lshift(snum,num,norm_shift);
 169         snum->neg=0;
 170         div_n=sdiv->top;
 171         num_n=snum->top;
 172         loop=num_n-div_n;
 173
 174         /* Lets setup a 'window' into snum
 175          * This is the part that corresponds to the current
 176          * 'area' being divided */
 177         BN_init(&wnum);
 178         wnum.d=  &(snum->d[loop]);
 179         wnum.top= div_n;
 180         wnum.max= snum->max+1; /* a bit of a lie */
 181
 182         /* Get the top 2 words of sdiv */
 183         /* i=sdiv->top; */
 184         d0=sdiv->d[div_n-1];
 185         d1=(div_n == 1)?0:sdiv->d[div_n-2];
 186
 187         /* pointer to the 'top' of snum */
 188         wnump= &(snum->d[num_n-1]);
 189
 190         /* Setup to 'res' */
 191         res->neg= (num->neg^divisor->neg);
 192         if (!bn_wexpand(res,(loop+1))) goto err;
 193         res->top=loop;
 194         resp= &(res->d[loop-1]);
 195
 196         /* space for temp */
 197         if (!bn_wexpand(tmp,(div_n+1))) goto err;
 198
 199         if (BN_ucmp(&wnum,sdiv) >= 0)
 200                 {
 201                 if (!BN_usub(&wnum,&wnum,sdiv)) goto err;
 202                 *resp=1;
 203                 res->d[res->top-1]=1;
 204                 }
 205         else
 206                 res->top--;
 207         resp--;
 208
 209         for (i=0; i<loop-1; i++)
 210                 {
 211                 BN_ULONG q,n0,n1;
 212                 BN_ULONG l0;
 213
 214                 wnum.d--; wnum.top++;
 215                 n0=wnump[0];
 216                 n1=wnump[-1];
 217                 if (n0 == d0)
 218                         q=BN_MASK2;
 219                 else
 220                         q=bn_div_words(n0,n1,d0);
 221                 {
 222 #ifdef BN_LLONG
 223                 BN_ULLONG t1,t2,rem;
 224                 t1=((BN_ULLONG)n0<<BN_BITS2)|n1;
 225                 for (;;)
 226                         {
 227                         t2=(BN_ULLONG)d1*q;
 228                         rem=t1-(BN_ULLONG)q*d0;
 229                         if ((rem>>BN_BITS2) ||
 230                                 (t2 <= ((BN_ULLONG)(rem<<BN_BITS2)+wnump[-2])))
 231                                 break;
 232                         q--;
 233                         }
 234 #else
 235                 BN_ULONG t1l,t1h,t2l,t2h,t3l,t3h,ql,qh,t3t;
 236                 t1h=n0;
 237                 t1l=n1;
 238                 for (;;)
 239                         {
 240                         t2l=LBITS(d1); t2h=HBITS(d1);
 241                         ql =LBITS(q);  qh =HBITS(q);
 242                         mul64(t2l,t2h,ql,qh); /* t2=(BN_ULLONG)d1*q; */
 243
 244                         t3t=LBITS(d0); t3h=HBITS(d0);
 245                         mul64(t3t,t3h,ql,qh); /* t3=t1-(BN_ULLONG)q*d0; */
 246                         t3l=(t1l-t3t)&BN_MASK2;
 247                         if (t3l > t1l) t3h++;
 248                         t3h=(t1h-t3h)&BN_MASK2;
 249
 250                         /*if ((t3>>BN_BITS2) ||
 251                                 (t2 <= ((t3<<BN_BITS2)+wnump[-2])))
 252                                 break; */
 253                         if (t3h) break;
 254                         if (t2h < t3l) break;
 255                         if ((t2h == t3l) && (t2l <= wnump[-2])) break;
 256
 257                         q--;
 258                         }
 259 #endif
 260                 }
 261                 l0=bn_mul_words(tmp->d,sdiv->d,div_n,q);
 262                 tmp->d[div_n]=l0;
 263                 for (j=div_n+1; j>0; j--)
 264                         if (tmp->d[j-1]) break;
 265                 tmp->top=j;
 266
 267                 j=wnum.top;
 268                 BN_sub(&wnum,&wnum,tmp);
 269
 270                 snum->top=snum->top+wnum.top-j;
 271
 272                 if (wnum.neg)
 273                         {
 274                         q--;
 275                         j=wnum.top;
 276                         BN_add(&wnum,&wnum,sdiv);
 277                         snum->top+=wnum.top-j;
 278                         }
 279                 *(resp--)=q;
 280                 wnump--;
 281                 }
 282         if (rm != NULL)
 283                 {
 284                 BN_rshift(rm,snum,norm_shift);
 285                 rm->neg=num->neg;
 286                 }
 287         return(1);
 288 err:
 289         return(0);
 290         }
 291
 292 #endif
 293
 294 /* rem != m */
 295 int BN_mod(rem, m, d,ctx)
 296 BIGNUM *rem;
 297 BIGNUM *m;
 298 BIGNUM *d;
 299 BN_CTX *ctx;
 300         {
 301 #if 0 /* The old slow way */
 302         int i,nm,nd;
 303         BIGNUM *dv;
 304
 305         if (BN_ucmp(m,d) < 0)
 306                 return((BN_copy(rem,m) == NULL)?0:1);
 307
 308         dv= &(ctx->bn[ctx->tos]);
 309
 310         if (!BN_copy(rem,m)) return(0);
 311
 312         nm=BN_num_bits(rem);
 313         nd=BN_num_bits(d);
 314         if (!BN_lshift(dv,d,nm-nd)) return(0);
 315         for (i=nm-nd; i>=0; i--)
 316                 {
 317                 if (BN_cmp(rem,dv) >= 0)
 318                         {
 319                         if (!BN_sub(rem,rem,dv)) return(0);
 320                         }
 321                 if (!BN_rshift1(dv,dv)) return(0);
 322                 }
 323         return(1);
 324 #else
 325         return(BN_div(NULL,rem,m,d,ctx));
 326 #endif
 327         }
 328