bn_shift.c: minimize reallocations, which allows BN_FLG_STATIC_DATA to
authorAndy Polyakov <appro@openssl.org>
Mon, 17 Oct 2011 17:20:48 +0000 (17:20 +0000)
committerAndy Polyakov <appro@openssl.org>
Mon, 17 Oct 2011 17:20:48 +0000 (17:20 +0000)
be shifted in specific cases.

crypto/bn/bn_shift.c

index c4d301a..a6fca2c 100644 (file)
@@ -99,7 +99,7 @@ int BN_lshift1(BIGNUM *r, const BIGNUM *a)
 int BN_rshift1(BIGNUM *r, const BIGNUM *a)
        {
        BN_ULONG *ap,*rp,t,c;
-       int i;
+       int i,j;
 
        bn_check_top(r);
        bn_check_top(a);
@@ -109,22 +109,25 @@ int BN_rshift1(BIGNUM *r, const BIGNUM *a)
                BN_zero(r);
                return(1);
                }
+       i = a->top;
+       ap= a->d;
+       j = i-(ap[i-1]==1);
        if (a != r)
                {
-               if (bn_wexpand(r,a->top) == NULL) return(0);
-               r->top=a->top;
+               if (bn_wexpand(r,j) == NULL) return(0);
                r->neg=a->neg;
                }
-       ap=a->d;
        rp=r->d;
-       c=0;
-       for (i=a->top-1; i>=0; i--)
+       t=ap[--i];
+       c=(t&1)?BN_TBIT:0;
+       if (t>>=1) rp[i]=t;
+       while (i>0)
                {
-               t=ap[i];
+               t=ap[--i];
                rp[i]=((t>>1)&BN_MASK2)|c;
                c=(t&1)?BN_TBIT:0;
                }
-       bn_correct_top(r);
+       r->top=j;
        bn_check_top(r);
        return(1);
        }
@@ -182,10 +185,11 @@ int BN_rshift(BIGNUM *r, const BIGNUM *a, int n)
                BN_zero(r);
                return(1);
                }
+       i = (BN_num_bits(a)-n+(BN_BITS2-1))/BN_BITS2;
        if (r != a)
                {
                r->neg=a->neg;
-               if (bn_wexpand(r,a->top-nw+1) == NULL) return(0);
+               if (bn_wexpand(r,i) == NULL) return(0);
                }
        else
                {
@@ -196,7 +200,7 @@ int BN_rshift(BIGNUM *r, const BIGNUM *a, int n)
        f= &(a->d[nw]);
        t=r->d;
        j=a->top-nw;
-       r->top=j;
+       r->top=i;
 
        if (rb == 0)
                {
@@ -212,9 +216,8 @@ int BN_rshift(BIGNUM *r, const BIGNUM *a, int n)
                        l= *(f++);
                        *(t++) =(tmp|(l<<lb))&BN_MASK2;
                        }
-               *(t++) =(l>>rb)&BN_MASK2;
+               if ((l = (l>>rb)&BN_MASK2)) *(t) = l;
                }
-       bn_correct_top(r);
        bn_check_top(r);
        return(1);
        }