Split Montgomery reduction into two functions, the core algorithm linked

as C (for replacing by asm later), and another that performs a subtract
if needed (inside powm_mnt.cpp). That way an asm version of the Montgomery
algorithm won't have to deal with calling other functions.

1 files changed, 12 insertions, 0 deletions

diff --git a/src/powm_mnt.cpp b/src/powm_mnt.cpp
index ad1ac312c..d28bfacfe 100644
--- a/src/powm_mnt.cpp
+++ b/src/powm_mnt.cpp
@@ -12,6 +12,18 @@ namespace Botan {
 namespace {
 
 /*************************************************
+* Montgomery Reduction                           *
+*************************************************/
+void montgomery_reduce(word z[], u32bit z_size,
+                       const word x[], u32bit x_size, word u)
+   {
+   bigint_monty_redc(z, z_size, x, x_size, u);
+
+   if(bigint_cmp(z + x_size, x_size + 1, x, x_size) >= 0)
+      bigint_sub2(z + x_size, x_size + 1, x, x_size);
+   }
+
+/*************************************************
 * Try to choose a good window size               *
 *************************************************/
 u32bit choose_window_bits(u32bit exp_bits, u32bit,