1 files changed, 76 insertions, 0 deletions
diff --git a/src/bigint/monty_generic/mp_monty.cpp b/src/bigint/monty_generic/mp_monty.cpp
new file mode 100644
index 000000000..c162bfd4f
--- /dev/null
+++ b/src/bigint/monty_generic/mp_monty.cpp
@@ -0,0 +1,76 @@
+/*************************************************
+* Montgomery Reduction Source File               *
+* (C) 1999-2008 Jack Lloyd                       *
+*     2006 Luca Piccarreta                       *
+*************************************************/
+
+#include <botan/mp_core.h>
+#include <botan/mp_asm.h>
+#include <botan/mp_asmi.h>
+
+namespace Botan {
+
+extern "C" {
+
+/*************************************************
+* Montgomery Reduction Algorithm                 *
+*************************************************/
+void bigint_monty_redc(word z[], u32bit z_size,
+                       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;
+
+      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;
+
+      for(u32bit j = x_size + 1; carry && j != z_size - i; ++j)
+         {
+         ++z_i[j];
+         carry = !z_i[j];
+         }
+      }
+
+   // Check if z[x_size...x_size+1] >= x[0...x_size] using bigint_cmp (inlined)
+   if(!z[x_size + x_size])
+      {
+      for(u32bit i = x_size; i > 0; --i)
+         {
+         if(z[x_size + i - 1] > x[i-1])
+            break;
+
+         if(z[x_size + i - 1] < x[i-1])
+            return;
+         }
+      }
+
+   // If the compare above is true, subtract using bigint_sub2 (inlined)
+   word carry = 0;
+
+   for(u32bit i = 0; i != blocks_of_8; i += 8)
+      carry = word8_sub2(z + x_size + i, x + i, carry);
+
+   for(u32bit i = blocks_of_8; i != x_size; ++i)
+      z[x_size + i] = word_sub(z[x_size + i], x[i], &carry);
+
+   if(carry)
+      --z[x_size+x_size];
+   }
+
+}
+
+}