Import Tcl 8.6.10

libtommath/bn_mp_montgomery_calc_normalization.c

@@ -0,0 +1,44 @@
+#include "tommath_private.h"
+#ifdef BN_MP_MONTGOMERY_CALC_NORMALIZATION_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+/*
+ * shifts with subtractions when the result is greater than b.
+ *
+ * The method is slightly modified to shift B unconditionally upto just under
+ * the leading bit of b.  This saves alot of multiple precision shifting.
+ */
+mp_err mp_montgomery_calc_normalization(mp_int *a, const mp_int *b)
+{
+   int    x, bits;
+   mp_err err;
+
+   /* how many bits of last digit does b use */
+   bits = mp_count_bits(b) % MP_DIGIT_BIT;
+
+   if (b->used > 1) {
+      if ((err = mp_2expt(a, ((b->used - 1) * MP_DIGIT_BIT) + bits - 1)) != MP_OKAY) {
+         return err;
+      }
+   } else {
+      mp_set(a, 1uL);
+      bits = 1;
+   }
+
+
+   /* now compute C = A * B mod b */
+   for (x = bits - 1; x < (int)MP_DIGIT_BIT; x++) {
+      if ((err = mp_mul_2(a, a)) != MP_OKAY) {
+         return err;
+      }
+      if (mp_cmp_mag(a, b) != MP_LT) {
+         if ((err = s_mp_sub(a, b, a)) != MP_OKAY) {
+            return err;
+         }
+      }
+   }
+
+   return MP_OKAY;
+}
+#endif