From b632667ce57af89691407bb8668e1512775278ae Mon Sep 17 00:00:00 2001
From: Calvin <calvin@EESI>
Date: Fri, 15 Mar 2013 15:26:20 -0400
Subject: nbc added

---
 src/nbc/kahan.sml | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)
 create mode 100644 src/nbc/kahan.sml

(limited to 'src/nbc/kahan.sml')

diff --git a/src/nbc/kahan.sml b/src/nbc/kahan.sml
new file mode 100644
index 0000000..70c6b47
--- /dev/null
+++ b/src/nbc/kahan.sml
@@ -0,0 +1,31 @@
+(* Kahan summation *)
+
+signature KAHAN = sig
+	type t
+	val zero: t
+	val add: t * real -> t
+	val sum: t -> real
+	val sequence: real Sequence.t -> real
+	val list: real list -> real
+	val array: real array -> real
+end
+
+structure Kahan :> KAHAN = struct
+	type t = real * real
+	val zero = (0.0, 0.0)
+	fun add ((s, c), x) =
+		let
+			val y = x - c
+			val t = s + y
+		in
+			(t, t - s - y)
+		end
+	fun sum (s, c) = s
+	local
+		fun swappedAdd (a, b) = add (b, a)
+	in
+		fun sequence e = sum (Sequence.fold swappedAdd zero e)
+		fun list l = sum (foldl swappedAdd zero l)
+		fun array a = sum (Array.foldl swappedAdd zero a)
+	end
+end
-- 
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