+#ifdef BN_RECURSION
+/* r is 2*n words in size,
+ * a and b are both n words in size. (There's not actually a 'b' here ...)
+ * n must be a power of 2.
+ * We multiply and return the result.
+ * t must be 2*n words in size
+ * We calculate
+ * a[0]*b[0]
+ * a[0]*b[0]+a[1]*b[1]+(a[0]-a[1])*(b[1]-b[0])
+ * a[1]*b[1]
+ */
+void bn_sqr_recursive(BN_ULONG *r, const BN_ULONG *a, int n2, BN_ULONG *t)
+ {
+ int n=n2/2;
+ int zero,c1;
+ BN_ULONG ln,lo,*p;
+
+#ifdef BN_COUNT
+ fprintf(stderr," bn_sqr_recursive %d * %d\n",n2,n2);
+#endif
+ if (n2 == 4)
+ {
+#ifndef BN_SQR_COMBA
+ bn_sqr_normal(r,a,4,t);
+#else
+ bn_sqr_comba4(r,a);
+#endif
+ return;
+ }
+ else if (n2 == 8)
+ {
+#ifndef BN_SQR_COMBA
+ bn_sqr_normal(r,a,8,t);
+#else
+ bn_sqr_comba8(r,a);
+#endif
+ return;
+ }
+ if (n2 < BN_SQR_RECURSIVE_SIZE_NORMAL)
+ {
+ bn_sqr_normal(r,a,n2,t);
+ return;
+ }
+ /* r=(a[0]-a[1])*(a[1]-a[0]) */
+ c1=bn_cmp_words(a,&(a[n]),n);
+ zero=0;
+ if (c1 > 0)
+ bn_sub_words(t,a,&(a[n]),n);
+ else if (c1 < 0)
+ bn_sub_words(t,&(a[n]),a,n);
+ else
+ zero=1;
+
+ /* The result will always be negative unless it is zero */
+ p= &(t[n2*2]);
+
+ if (!zero)
+ bn_sqr_recursive(&(t[n2]),t,n,p);
+ else
+ memset(&(t[n2]),0,n*sizeof(BN_ULONG));
+ bn_sqr_recursive(r,a,n,p);
+ bn_sqr_recursive(&(r[n2]),&(a[n]),n,p);
+
+ /* t[32] holds (a[0]-a[1])*(a[1]-a[0]), it is negative or zero
+ * r[10] holds (a[0]*b[0])
+ * r[32] holds (b[1]*b[1])
+ */
+
+ c1=(int)(bn_add_words(t,r,&(r[n2]),n2));
+
+ /* t[32] is negative */
+ c1-=(int)(bn_sub_words(&(t[n2]),t,&(t[n2]),n2));
+
+ /* t[32] holds (a[0]-a[1])*(a[1]-a[0])+(a[0]*a[0])+(a[1]*a[1])
+ * r[10] holds (a[0]*a[0])
+ * r[32] holds (a[1]*a[1])
+ * c1 holds the carry bits
+ */
+ c1+=(int)(bn_add_words(&(r[n]),&(r[n]),&(t[n2]),n2));
+ if (c1)
+ {
+ p= &(r[n+n2]);
+ lo= *p;
+ ln=(lo+c1)&BN_MASK2;
+ *p=ln;
+
+ /* The overflow will stop before we over write
+ * words we should not overwrite */
+ if (ln < (BN_ULONG)c1)
+ {
+ do {
+ p++;
+ lo= *p;
+ ln=(lo+1)&BN_MASK2;
+ *p=ln;
+ } while (ln == 0);
+ }
+ }
+ }
+#endif