1 files changed, 42 insertions, 0 deletions
diff --git a/src/libstrongswan/math/libnttfft/ntt_fft_reduce.h b/src/libstrongswan/math/libnttfft/ntt_fft_reduce.h
new file mode 100644
index 000000000..5ff2b9588
--- /dev/null
+++ b/src/libstrongswan/math/libnttfft/ntt_fft_reduce.h
@@ -0,0 +1,42 @@
+/*
+ * Copyright (C) 2016 Andreas Steffen
+ * HSR Hochschule fuer Technik Rapperswil
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation; either version 2 of the License, or (at your
+ * option) any later version.  See <http://www.fsf.org/copyleft/gpl.txt>.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * for more details.
+ */
+
+/**
+ * @defgroup ntt_fft ntt_fft
+ * @{ @ingroup ntt_p
+ */
+
+#ifndef NTT_REDUCE_H_
+#define NTT_REDUCE_H_
+
+#include "ntt_fft_params.h"
+
+/**
+ * Montgomery Reduction
+ *
+ * Montgomery, P. L. Modular multiplication without trial division.
+ * Mathematics of Computation 44, 170 (1985), 519–521.
+ */
+static inline uint32_t ntt_fft_mreduce(uint32_t x, const ntt_fft_params_t *p)
+{
+	uint32_t m, t;
+	
+	m = (x * p->q_inv) & p->rmask;
+	t = (x + m * p->q) >> p->rlog;
+
+	return (t < p->q) ? t : t - p->q;
+}
+
+#endif /** NTT_REDUCE_H_ @}*/