From 954105d1ac1855d8f8e2e340a29cbc977bf72dbf Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Tue, 2 Mar 2021 09:58:24 -0800
Subject: [PATCH] ircd::math: Add mean suite.

---
 include/ircd/math/math.h |  1 +
 include/ircd/math/mean.h | 65 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+)
 create mode 100644 include/ircd/math/mean.h

diff --git a/include/ircd/math/math.h b/include/ircd/math/math.h
index b8c1cd276..88a423e5b 100644
--- a/include/ircd/math/math.h
+++ b/include/ircd/math/math.h
@@ -13,3 +13,4 @@
 
 #include "log2.h"
 #include "inv.h"
+#include "mean.h"
diff --git a/include/ircd/math/mean.h b/include/ircd/math/mean.h
new file mode 100644
index 000000000..c24da44d6
--- /dev/null
+++ b/include/ircd/math/mean.h
@@ -0,0 +1,65 @@
+// Matrix Construct
+//
+// Copyright (C) Matrix Construct Developers, Authors & Contributors
+// Copyright (C) 2016-2021 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_MEAN_H
+
+namespace ircd::math
+{
+	template<class T>
+	typename std::enable_if<!simd::is<T>(), T>::type
+	mean(const vector_view<const T> &);
+
+	template<class T>
+	typename std::enable_if<simd::is<T>(), simd::lane_type<T>>::type
+	mean(const vector_view<const T> &);
+}
+
+template<class T>
+inline typename std::enable_if<ircd::simd::is<T>(), ircd::simd::lane_type<T>>::type
+ircd::math::mean(const vector_view<const T> &a)
+{
+	using value_type = simd::lane_type<T>;
+
+	const auto &sum
+	{
+		simd::accumulate(a.data(), u64x2{0, a.size()}, T{0}, []
+		(auto &ret, const auto block, const auto mask)
+		{
+			ret += block;
+		})
+	};
+
+	value_type num {0};
+	for(size_t i{0}; i < simd::lanes<T>(); ++i)
+		num += sum[i];
+
+	const auto &den
+	{
+		a.size() * simd::lanes<T>()
+	};
+
+	num /= den;
+	return num;
+}
+
+template<class T>
+inline typename std::enable_if<!ircd::simd::is<T>(), T>::type
+ircd::math::mean(const vector_view<const T> &a)
+{
+	T ret{0};
+
+	size_t i{0};
+	while(i < a.size())
+		ret += a[i++];
+
+	ret /= i;
+	return ret;
+}