ircd::math: Add difference template convenience.

include/ircd/math/diff.h

@@ -0,0 +1,48 @@
+// Matrix Construct
+//
+// Copyright (C) Matrix Construct Developers, Authors & Contributors
+// Copyright (C) 2016-2022 Jason Volk <jason@zemos.net>
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice is present in all copies. The
+// full license for this software is available in the LICENSE file.
+
+#pragma once
+#define HAVE_IRCD_MATH_DIFF_H
+
+namespace ircd::math
+{
+	template<class T>
+	typename std::enable_if<!simd::is<T>(), T>::type
+	diff(const T, const T);
+
+	template<class T>
+	typename std::enable_if<simd::is<T>(), T>::type
+	diff(const T, const T);
+}
+
+namespace ircd
+{
+	using math::diff;
+}
+
+template<class T>
+inline typename std::enable_if<ircd::simd::is<T>(), T>::type
+ircd::math::diff(const T a, const T b)
+{
+	T r;
+	for(uint i(0); i < simd::lanes<T>(); ++i)
+		r[i] = diff(a[i], b[i]);
+
+	return r;
+}
+
+template<class T>
+inline typename std::enable_if<!ircd::simd::is<T>(), T>::type
+ircd::math::diff(const T a, const T b)
+{
+	return a > b?
+		a - b:
+		b - a;
+}

include/ircd/math/math.h

@@ -12,6 +12,7 @@
 #define HAVE_IRCD_MATH_MATH_H
 
 #include "log2.h"
+#include "diff.h"
 #include "inv.h"
 #include "mean.h"
 #include "tanh.h"