1 files changed, 72 insertions, 0 deletions
diff --git a/src/math/mp/monty_generic/mp_monty.cpp b/src/math/mp/monty_generic/mp_monty.cpp
new file mode 100644
index 000000000..bce35259a
--- /dev/null
+++ b/src/math/mp/monty_generic/mp_monty.cpp
@@ -0,0 +1,72 @@
+/*
+* Montgomery Reduction
+* (C) 1999-2010 Jack Lloyd
+*     2006 Luca Piccarreta
+*
+* Distributed under the terms of the Botan license
+*/
+
+#include <botan/internal/mp_core.h>
+#include <botan/internal/mp_asm.h>
+#include <botan/internal/mp_asmi.h>
+#include <botan/mem_ops.h>
+
+namespace Botan {
+
+extern "C" {
+
+/*
+* Montgomery Reduction Algorithm
+*/
+void bigint_monty_redc(word z[], u32bit z_size,
+                       word ws[],
+                       const word x[], u32bit x_size,
+                       word u)
+   {
+   const u32bit blocks_of_8 = x_size - (x_size % 8);
+
+   for(u32bit i = 0; i != x_size; ++i)
+      {
+      word* z_i = z + i;
+
+      const word y = z_i[0] * u;
+
+      /*
+      bigint_linmul3(ws, x, x_size, y);
+      bigint_add2(z_i, z_size - i, ws, x_size+1);
+      */
+      word carry = 0;
+
+      for(u32bit j = 0; j != blocks_of_8; j += 8)
+         carry = word8_madd3(z_i + j, x + j, y, carry);
+
+      for(u32bit j = blocks_of_8; j != x_size; ++j)
+         z_i[j] = word_madd3(x[j], y, z_i[j], &carry);
+
+      word z_sum = z_i[x_size] + carry;
+      carry = (z_sum < z_i[x_size]);
+      z_i[x_size] = z_sum;
+
+      // Note: not constant time
+      for(u32bit j = x_size + 1; carry && j != z_size - i; ++j)
+         {
+         ++z_i[j];
+         carry = !z_i[j];
+         }
+      }
+
+   word borrow = 0;
+   for(u32bit i = 0; i != x_size; ++i)
+      ws[i] = word_sub(z[x_size + i], x[i], &borrow);
+
+   ws[x_size] = word_sub(z[x_size+x_size], 0, &borrow);
+
+   copy_mem(ws + x_size + 1, z + x_size, x_size + 1);
+
+   copy_mem(z, ws + borrow*(x_size+1), x_size + 1);
+   clear_mem(z + x_size + 1, z_size - x_size - 1);
+   }
+
+}
+
+}