Bignum library bug fix. IRIX 6 passes "make test" now!
[openssl.git] / crypto / bn / bn_lib.c
index bd53124..64c9fd9 100644 (file)
@@ -150,7 +150,7 @@ char *BN_options(void)
 
 int BN_num_bits_word(BN_ULONG l)
        {
-       static char bits[256]={
+       static const char bits[256]={
                0,1,2,2,3,3,3,3,4,4,4,4,4,4,4,4,
                5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
                6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
@@ -343,8 +343,9 @@ void BN_CTX_free(BN_CTX *c)
 
 BIGNUM *bn_expand2(BIGNUM *b, int words)
        {
-       BN_ULONG *A,*B,*a;
-       int i,j;
+       BN_ULONG *A,*a;
+       const BN_ULONG *B;
+       int i;
 
        bn_check_top(b);
 
@@ -362,15 +363,38 @@ BIGNUM *bn_expand2(BIGNUM *b, int words)
                        BNerr(BN_F_BN_EXPAND2,ERR_R_MALLOC_FAILURE);
                        return(NULL);
                        }
-memset(A,0x5c,sizeof(BN_ULONG)*(words+1));
 #if 1
                B=b->d;
                /* Check if the previous number needs to be copied */
                if (B != NULL)
                        {
+#if 0
                        /* This lot is an unrolled loop to copy b->top 
                         * BN_ULONGs from B to A
                         */
+/*
+ * I have nothing against unrolling but it's usually done for
+ * several reasons, namely:
+ * - minimize percentage of decision making code, i.e. branches;
+ * - avoid cache trashing;
+ * - make it possible to schedule loads earlier;
+ * Now let's examine the code below. The cornerstone of C is
+ * "programmer is always right" and that's what we love it for:-)
+ * For this very reason C compilers have to be paranoid when it
+ * comes to data aliasing and assume the worst. Yeah, but what
+ * does it mean in real life? This means that loop body below will
+ * be compiled to sequence of loads immediately followed by stores
+ * as compiler assumes the worst, something in A==B+1 style. As a
+ * result CPU pipeline is going to starve for incoming data. Secondly
+ * if A and B happen to share same cache line such code is going to
+ * cause severe cache trashing. Both factors have severe impact on
+ * performance of modern CPUs and this is the reason why this
+ * particulare piece of code is #ifdefed away and replaced by more
+ * "friendly" version found in #else section below. This comment
+ * also applies to BN_copy function.
+ *
+ *                                     <appro@fy.chalmers.se>
+ */
                        for (i=b->top&(~7); i>0; i-=8)
                                {
                                A[0]=B[0]; A[1]=B[1]; A[2]=B[2]; A[3]=B[3];
@@ -407,6 +431,30 @@ memset(A,0x5c,sizeof(BN_ULONG)*(words+1));
                                 */
                                ;
                                }
+#else
+                       for (i=b->top>>2; i>0; i--,A+=4,B+=4)
+                               {
+                               /*
+                                * The fact that the loop is unrolled
+                                * 4-wise is a tribute to Intel. It's
+                                * the one that doesn't have enough
+                                * registers to accomodate more data.
+                                * I'd unroll it 8-wise otherwise:-)
+                                *
+                                *              <appro@fy.chalmers.se>
+                                */
+                               BN_ULONG a0,a1,a2,a3;
+                               a0=B[0]; a1=B[1]; a2=B[2]; a3=B[3];
+                               A[0]=a0; A[1]=a1; A[2]=a2; A[3]=a3;
+                               }
+                       switch (b->top&3)
+                               {
+                               case 3: A[2]=B[2];
+                               case 2: A[1]=B[1];
+                               case 1: A[0]=B[0];
+                               case 0: ; /* ultrix cc workaround, see above */
+                               }
+#endif
                        Free(b->d);
                        }
 
@@ -415,22 +463,19 @@ memset(A,0x5c,sizeof(BN_ULONG)*(words+1));
 
                /* Now need to zero any data between b->top and b->max */
 
-               B= &(b->d[b->top]);
-               j=(b->max - b->top) & ~7;
-               for (i=0; i<j; i+=8)
+               A= &(b->d[b->top]);
+               for (i=(b->max - b->top)>>3; i>0; i--,A+=8)
                        {
-                       B[0]=0; B[1]=0; B[2]=0; B[3]=0;
-                       B[4]=0; B[5]=0; B[6]=0; B[7]=0;
-                       B+=8;
-                       }
-               j=(b->max - b->top) & 7;
-               for (i=0; i<j; i++)
-                       {
-                       B[0]=0;
-                       B++;
+                       A[0]=0; A[1]=0; A[2]=0; A[3]=0;
+                       A[4]=0; A[5]=0; A[6]=0; A[7]=0;
                        }
+               for (i=(b->max - b->top)&7; i>0; i--,A++)
+                       A[0]=0;
 #else
-                       memcpy(a->d,b->d,sizeof(b->d[0])*b->top);
+                       memset(A,0,sizeof(BN_ULONG)*(words+1));
+                       memcpy(A,b->d,sizeof(b->d[0])*b->top);
+                       b->d=a;
+                       b->max=words;
 #endif
                
 /*             memset(&(p[b->max]),0,((words+1)-b->max)*sizeof(BN_ULONG)); */
@@ -454,7 +499,8 @@ BIGNUM *BN_dup(BIGNUM *a)
 BIGNUM *BN_copy(BIGNUM *a, BIGNUM *b)
        {
        int i;
-       BN_ULONG *A,*B;
+       BN_ULONG *A;
+       const BN_ULONG *B;
 
        bn_check_top(b);
 
@@ -464,47 +510,18 @@ BIGNUM *BN_copy(BIGNUM *a, BIGNUM *b)
 #if 1
        A=a->d;
        B=b->d;
-       for (i=b->top&(~7); i>0; i-=8)
+       for (i=b->top>>2; i>0; i--,A+=4,B+=4)
                {
-               A[0]=B[0];
-               A[1]=B[1];
-               A[2]=B[2];
-               A[3]=B[3];
-               A[4]=B[4];
-               A[5]=B[5];
-               A[6]=B[6];
-               A[7]=B[7];
-               A+=8;
-               B+=8;
+               BN_ULONG a0,a1,a2,a3;
+               a0=B[0]; a1=B[1]; a2=B[2]; a3=B[3];
+               A[0]=a0; A[1]=a1; A[2]=a2; A[3]=a3;
                }
-       switch (b->top&7)
+       switch (b->top&3)
                {
-       case 7:
-               A[6]=B[6];
-       case 6:
-               A[5]=B[5];
-       case 5:
-               A[4]=B[4];
-       case 4:
-               A[3]=B[3];
-       case 3:
-               A[2]=B[2];
-       case 2:
-               A[1]=B[1];
-       case 1:
-               A[0]=B[0];
-        case 0:
-               /* I need the 'case 0' entry for utrix cc.
-                * If the optimiser is turned on, it does the
-                * switch table by doing
-                * a=top&7
-                * a--;
-                * goto jump_table[a];
-                * If top is 0, this makes us jump to 0xffffffc which is
-                * rather bad :-(.
-                * eric 23-Apr-1998
-                */
-               ;
+               case 3: A[2]=B[2];
+               case 2: A[1]=B[1];
+               case 1: A[0]=B[0];
+               case 0: ; /* ultrix cc workaround, see comments in bn_expand2 */
                }
 #else
        memcpy(a->d,b->d,sizeof(b->d[0])*b->top);
@@ -539,6 +556,8 @@ BN_ULONG BN_get_word(BIGNUM *a)
 #ifndef SIXTY_FOUR_BIT /* the data item > unsigned long */
                ret<<=BN_BITS4; /* stops the compiler complaining */
                ret<<=BN_BITS4;
+#else
+               ret=0;
 #endif
                ret|=a->d[i];
                }
@@ -563,6 +582,8 @@ int BN_set_word(BIGNUM *a, BN_ULONG w)
 #ifndef SIXTY_FOUR_BIT /* the data item > unsigned long */
                w>>=BN_BITS4;
                w>>=BN_BITS4;
+#else
+               w=0;
 #endif
                a->d[i]=(BN_ULONG)w&BN_MASK2;
                if (a->d[i] != 0) a->top=i+1;
@@ -699,7 +720,7 @@ int BN_set_bit(BIGNUM *a, int n)
                a->top=i+1;
                }
 
-       a->d[i]|=(1L<<j);
+       a->d[i]|=(((BN_ULONG)1)<<j);
        return(1);
        }
 
@@ -711,7 +732,7 @@ int BN_clear_bit(BIGNUM *a, int n)
        j=n%BN_BITS2;
        if (a->top <= i) return(0);
 
-       a->d[i]&=(~(1L<<j));
+       a->d[i]&=(~(((BN_ULONG)1)<<j));
        bn_fix_top(a);
        return(1);
        }