--- /dev/null
+/* TomsFastMath, a fast ISO C bignum library.
+ *
+ * This project is meant to fill in where LibTomMath
+ * falls short. That is speed ;-)
+ *
+ * This project is public domain and free for all purposes.
+ *
+ * Tom St Denis, tomstdenis@gmail.com
+ */
+#include <tfm_private.h>
+
+/* computes a = B**n mod b without division or multiplication useful for
+ * normalizing numbers in a Montgomery system.
+ */
+void fp_montgomery_calc_normalization(fp_int *a, fp_int *b)
+{
+ int x, bits;
+
+ /* how many bits of last digit does b use */
+ bits = fp_count_bits (b) % DIGIT_BIT;
+ if (!bits) bits = DIGIT_BIT;
+
+ /* compute A = B^(n-1) * 2^(bits-1) */
+ if (b->used > 1) {
+ fp_2expt (a, (b->used - 1) * DIGIT_BIT + bits - 1);
+ } else {
+ fp_set(a, 1);
+ bits = 1;
+ }
+
+ /* now compute C = A * B mod b */
+ for (x = bits - 1; x < (int)DIGIT_BIT; x++) {
+ fp_mul_2 (a, a);
+ if (fp_cmp_mag (a, b) != FP_LT) {
+ s_fp_sub (a, b, a);
+ }
+ }
+}
+
+
+/* $Source$ */
+/* $Revision$ */
+/* $Date$ */