+ ap=&(r->d[ri]);
+ nrp=ap;
+
+ /* This 'if' denotes violation of 2*M<r^(n-1) boundary condition
+ * formulated by C.D.Walter in "Montgomery exponentiation needs
+ * no final subtractions." Incurred branch can disclose only
+ * information about modulus length, which is not really secret. */
+ if ((mont->N.d[ri-1]>>(BN_BITS2-2))!=0)
+ {
+ size_t m1,m2;
+
+ v=bn_sub_words(rp,ap,mont->N.d,ri);
+ /* this -----------------------^^ works even in al<ri case
+ * thanks to zealous zeroing of top of the vector in the
+ * beginning. */
+
+ /* if (al==ri && !v) || al>ri) nrp=rp; else nrp=ap; */
+ /* in other words if subtraction result is real, then
+ * trick unconditional memcpy below to perform in-place
+ * "refresh" instead of actual copy. */
+ m1=0-(size_t)(((al-ri)>>(sizeof(al)*8-1))&1); /* al<ri */
+ m2=0-(size_t)(((ri-al)>>(sizeof(al)*8-1))&1); /* al>ri */
+ m1|=m2; /* (al!=ri) */
+ m1|=(0-(size_t)v); /* (al!=ri || v) */
+ m1&=~m2; /* (al!=ri || v) && !al>ri */
+ nrp=(BN_ULONG *)(((size_t)rp&~m1)|((size_t)ap&m1));
+ }
+
+ /* 'i<ri' is chosen to eliminate dependency on input data, even
+ * though it results in redundant copy in al<ri case. */
+ for (i=0,ri-=4; i<ri; i+=4)
+ {
+ BN_ULONG t1,t2,t3,t4;
+
+ t1=nrp[i+0];
+ t2=nrp[i+1];
+ t3=nrp[i+2]; ap[i+0]=0;
+ t4=nrp[i+3]; ap[i+1]=0;
+ rp[i+0]=t1; ap[i+2]=0;
+ rp[i+1]=t2; ap[i+3]=0;
+ rp[i+2]=t3;
+ rp[i+3]=t4;
+ }
+ for (ri+=4; i<ri; i++)
+ rp[i]=nrp[i], ap[i]=0;
+# else
+ if (bn_wexpand(ret,al) == NULL) goto err;