Bignum division tune-up. Idea is to move multiplications in front of

[openssl.git] / crypto / bn / bn_div.c

diff --git a/crypto/bn/bn_div.c b/crypto/bn/bn_div.c
index defcf90c8223d282b36306aa3737dc3b22ca7460..03b9152241798e5154c619c3f1b5ea0d332cd995 100644 (file)
--- a/crypto/bn/bn_div.c
+++ b/crypto/bn/bn_div.c
@@ -200,56 +200,69 @@ int BN_div(BIGNUM *dv, BIGNUM *rm, const BIGNUM *num, const BIGNUM *divisor,
 
        for (i=0; i<loop-1; i++)
                {
-               BN_ULONG q,n0,n1;
-               BN_ULONG l0;
+               BN_ULONG q,l0;
+#ifdef BN_DIV3W
+               q=bn_div_3_words(wnump,d0,d1);
+#else
+               BN_ULONG n0,n1,rem;
 
-               wnum.d--; wnum.top++;
                n0=wnump[0];
                n1=wnump[-1];
                if (n0 == d0)
                        q=BN_MASK2;
                else
+#if defined(BN_LLONG) && defined(BN_DIV2W)
+                       q=((((BN_ULLONG)n0)<<BN_BITS2)|n1)/((BN_ULLONG)d0);
+#else
                        q=bn_div_words(n0,n1,d0);
+#endif
                {
 #ifdef BN_LLONG
-               BN_ULLONG t1,t2,rem;
-               t1=((BN_ULLONG)n0<<BN_BITS2)|n1;
+               BN_ULLONG t2;
+
+               /*
+                * 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;
+
+               t2=(BN_ULLONG)d1*q;
                for (;;)
                        {
-                       rem=t1-(BN_ULLONG)q*d0;
-                       t2=(BN_ULLONG)d1*q;
-                        if ((rem>>BN_BITS2) ||
-                               (t2 <= ((rem<<BN_BITS2)|wnump[-2])))
+                        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 t1l,t1h,t2l,t2h,t3l,t3h,ql,qh,t3t;
-               t1h=n0;
-               t1l=n1;
+               BN_ULONG t2l,t2h,ql,qh;
+
+               /*
+                * It's more than enough with the only multiplication.
+                * See the comment above in BN_LLONG section...
+                */
+               rem=(n1-q*d0)&BN_MASK2;
+
+               t2l=LBITS(d1); t2h=HBITS(d1);
+               ql =LBITS(q);  qh =HBITS(q);
+               mul64(t2l,t2h,ql,qh); /* t2=(BN_ULLONG)d1*q; */
+
                for (;;)
                        {
-                       t2l=LBITS(d1); t2h=HBITS(d1);
-                       ql =LBITS(q);  qh =HBITS(q);
-                       mul64(t2l,t2h,ql,qh); /* t2=(BN_ULLONG)d1*q; */
-
-                       t3t=LBITS(d0); t3h=HBITS(d0);
-                       mul64(t3t,t3h,ql,qh); /* t3=t1-(BN_ULLONG)q*d0; */
-                       t3l=(t1l-t3t)&BN_MASK2;
-                       if (t3l > t1l) t3h++;
-                       t3h=(t1h-t3h)&BN_MASK2;
-
-                       /*if ((t3>>BN_BITS2) ||
-                               (t2 <= ((t3<<BN_BITS2)+wnump[-2])))
-                               break; */
-                       if (t3h) break;
-                       if (t2h < t3l) break;
-                       if ((t2h == t3l) && (t2l <= wnump[-2])) break;
-
+                       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
                }
+#endif /* BN_DIV3W */
+               wnum.d--; wnum.top++;
                l0=bn_mul_words(tmp->d,sdiv->d,div_n,q);
                tmp->d[div_n]=l0;
                for (j=div_n+1; j>0; j--)