BN_div bugfix. The q-- loop should not be entered in the n0==d0 case.
authorUlf Möller <ulf@openssl.org>
Sun, 6 Feb 2000 00:25:39 +0000 (00:25 +0000)
committerUlf Möller <ulf@openssl.org>
Sun, 6 Feb 2000 00:25:39 +0000 (00:25 +0000)
CHANGES
crypto/bn/bn_div.c

diff --git a/CHANGES b/CHANGES
index 131faa9..53e4c93 100644 (file)
--- a/CHANGES
+++ b/CHANGES
@@ -4,6 +4,10 @@
 
  Changes between 0.9.4 and 0.9.5  [xx XXX 2000]
 
+  *) Bug fix for BN_div() when the first words of num and divsor are
+     equal (it gave wrong results if (rem=(n1-q*d0)&BN_MASK2) < d0).
+     [Ulf Möller]
+
   *) Add support for various broken PKCS#8 formats, and command line
      options to produce them.
      [Steve Henson]
index 3505221..31062b7 100644 (file)
@@ -62,7 +62,7 @@
 #include "bn_lcl.h"
 
 /* The old slow way */
-#if 1
+#if 0
 int BN_div(BIGNUM *dv, BIGNUM *rem, const BIGNUM *m, const BIGNUM *d,
           BN_CTX *ctx)
        {
@@ -126,6 +126,32 @@ int BN_div(BIGNUM *dv, BIGNUM *rem, const BIGNUM *m, const BIGNUM *d,
 
 #else
 
+#if !defined(NO_ASM) && !defined(PEDANTIC) && !defined(BN_DIV3W)
+# if defined(__GNUC__) && __GNUC__>=2
+#  if defined(__i386)
+   /*
+    * There were two reasons for implementing this template:
+    * - GNU C generates a call to a function (__udivdi3 to be exact)
+    *   in reply to ((((BN_ULLONG)n0)<<BN_BITS2)|n1)/d0 (I fail to
+    *   understand why...);
+    * - divl doesn't only calculate quotient, but also leaves
+    *   remainder in %edx which we can definitely use here:-)
+    *
+    *                                  <appro@fy.chalmers.se>
+    */
+#  define bn_div_words(n0,n1,d0)               \
+       ({  asm volatile (                      \
+               "divl   %4"                     \
+               : "=a"(q), "=d"(rem)            \
+               : "a"(n1), "d"(n0), "g"(d0)     \
+               : "cc");                        \
+           q;                                  \
+       })
+#  define REMAINDER_IS_ALREADY_CALCULATED
+#  endif /* __<cpu> */
+# endif /* __GNUC__ */
+#endif /* NO_ASM */
+
 int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor,
           BN_CTX *ctx)
        {
@@ -214,103 +240,72 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor,
 #ifdef BN_DIV3W
                q=bn_div_3_words(wnump,d1,d0);
 #else
-
-#if !defined(NO_ASM) && !defined(PEDANTIC)
-# if defined(__GNUC__) && __GNUC__>=2
-#  if defined(__i386)
-   /*
-    * There were two reasons for implementing this template:
-    * - GNU C generates a call to a function (__udivdi3 to be exact)
-    *   in reply to ((((BN_ULLONG)n0)<<BN_BITS2)|n1)/d0 (I fail to
-    *   understand why...);
-    * - divl doesn't only calculate quotient, but also leaves
-    *   remainder in %edx which we can definitely use here:-)
-    *
-    *                                  <appro@fy.chalmers.se>
-    */
-#  define bn_div_words(n0,n1,d0)               \
-       ({  asm volatile (                      \
-               "divl   %4"                     \
-               : "=a"(q), "=d"(rem)            \
-               : "a"(n1), "d"(n0), "g"(d0)     \
-               : "cc");                        \
-           q;                                  \
-       })
-#  define REMAINDER_IS_ALREADY_CALCULATED
-#  endif /* __<cpu> */
-# endif /* __GNUC__ */
-#endif /* NO_ASM */
                BN_ULONG n0,n1,rem=0;
 
                n0=wnump[0];
                n1=wnump[-1];
                if (n0 == d0)
-                       {
                        q=BN_MASK2;
-#ifdef REMAINDER_IS_ALREADY_CALCULATED /* in this case it isn't */
-                       rem=(n1-q*d0)&BN_MASK2;
-#endif
-                       }
-               else /* n0 < d0 */
+               else                    /* n0 < d0 */
+                       {
+#ifdef BN_LLONG
+                       BN_ULLONG t2;
+
 #if defined(BN_LLONG) && defined(BN_DIV2W) && !defined(bn_div_words)
                        q=(BN_ULONG)(((((BN_ULLONG)n0)<<BN_BITS2)|n1)/d0);
 #else
                        q=bn_div_words(n0,n1,d0);
 #endif
-               {
-#ifdef BN_LLONG
-               BN_ULLONG t2;
 
 #ifndef REMAINDER_IS_ALREADY_CALCULATED
-               /*
-                * rem doesn't have to be BN_ULLONG. The least we
-                * know it's less that d0, isn't it?
-                */
-               rem=(n1-q*d0)&BN_MASK2;
+                       /*
+                        * rem doesn't have to be BN_ULLONG. The least we
+                        * know it's less that d0, isn't it?
+                        */
+                       rem=(n1-q*d0)&BN_MASK2;
 #endif
-               t2=(BN_ULLONG)d1*q;
-
-               for (;;)
-                       {
-                        if (t2 <= ((((BN_ULLONG)rem)<<BN_BITS2)|wnump[-2]))
-                               break;
-                       q--;
-                       rem += d0;
-                       if (rem < d0) break; /* don't let rem overflow */
-                       t2 -= d1;
-                       }
-#else
-               BN_ULONG t2l,t2h,ql,qh;
+                       t2=(BN_ULLONG)d1*q;
+
+                       for (;;)
+                               {
+                               if (t2 <= ((((BN_ULLONG)rem)<<BN_BITS2)|wnump[-2]))
+                                       break;
+                               q--;
+                               rem += d0;
+                               if (rem < d0) break; /* don't let rem overflow */
+                               t2 -= d1;
+                               }
+#else /* !BN_LLONG */
+                       BN_ULONG t2l,t2h,ql,qh;
 
+                       q=bn_div_words(n0,n1,d0);
 #ifndef REMAINDER_IS_ALREADY_CALCULATED
-               /*
-                * It's more than enough with the only multiplication.
-                * See the comment above in BN_LLONG section...
-                */
-               rem=(n1-q*d0)&BN_MASK2;
+                       rem=(n1-q*d0)&BN_MASK2;
 #endif
+
 #ifdef BN_UMULT_HIGH
-               t2l = d1 * q;
-               t2h = BN_UMULT_HIGH(d1,q);
+                       t2l = d1 * q;
+                       t2h = BN_UMULT_HIGH(d1,q);
 #else
-               t2l=LBITS(d1); t2h=HBITS(d1);
-               ql =LBITS(q);  qh =HBITS(q);
-               mul64(t2l,t2h,ql,qh); /* t2=(BN_ULLONG)d1*q; */
+                       t2l=LBITS(d1); t2h=HBITS(d1);
+                       ql =LBITS(q);  qh =HBITS(q);
+                       mul64(t2l,t2h,ql,qh); /* t2=(BN_ULLONG)d1*q; */
 #endif
 
-               for (;;)
-                       {
-                       if ((t2h < rem) ||
-                               ((t2h == rem) && (t2l <= wnump[-2])))
-                               break;
-                       q--;
-                       rem += d0;
-                       if (rem < d0) break; /* don't let rem overflow */
-                       if (t2l < d1) t2h--; t2l -= d1;
+                       for (;;)
+                               {
+                               if ((t2h < rem) ||
+                                       ((t2h == rem) && (t2l <= wnump[-2])))
+                                       break;
+                               q--;
+                               rem += d0;
+                               if (rem < d0) break; /* don't let rem overflow */
+                               if (t2l < d1) t2h--; t2l -= d1;
+                               }
+#endif /* !BN_LLONG */
                        }
-#endif
-               }
 #endif /* !BN_DIV3W */
+
                l0=bn_mul_words(tmp->d,sdiv->d,div_n,q);
                wnum.d--; wnum.top++;
                tmp->d[div_n]=l0;
@@ -341,7 +336,7 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor,
        BN_CTX_end(ctx);
        return(1);
 err:
-       BN_CX_end(ctx);
+       BN_CTX_end(ctx);
        return(0);
        }