From 8d3a6e83d8cd460b9b180523ce7b098c5a0c5c19 Mon Sep 17 00:00:00 2001
From: Ahmet Inan <inan@aicodix.de>
Date: Sun, 31 Mar 2019 21:59:16 +0200
Subject: [PATCH] added Hilbert transform filter

---
 README.md |  1 +
 filter.hh | 15 +++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/README.md b/README.md
index 94d06be..907af11 100644
--- a/README.md
+++ b/README.md
@@ -27,6 +27,7 @@ Implemented are the following [finite impulse response](https://en.wikipedia.org
 * [low-pass filter](https://en.wikipedia.org/wiki/Low-pass_filter)
 * [high-pass filter](https://en.wikipedia.org/wiki/High-pass_filter)
 * [band-pass filter](https://en.wikipedia.org/wiki/Band-pass_filter)
+* [Hilbert-transform filter](https://en.wikipedia.org/wiki/Hilbert_transform)
 
 ### [ema.hh](ema.hh)
 
diff --git a/filter.hh b/filter.hh
index 39a23d2..cb7d8ec 100644
--- a/filter.hh
+++ b/filter.hh
@@ -87,5 +87,20 @@ public:
 	}
 };
 
+template <typename TYPE>
+struct HilbertTransform
+{
+	TYPE operator () (int n, int N)
+	{
+		if (N&1) {
+			int x = n - (N - 1) / 2;
+			return x&1 ? TYPE(2) / (Const<TYPE>::Pi() * TYPE(x)) : TYPE(0);
+		} else {
+			TYPE x = TYPE(n) - TYPE(0.5) * TYPE(N - 1);
+			return TYPE(1) / (Const<TYPE>::Pi() * x);
+		}
+	}
+};
+
 }