From 19ff52a1d1ff2fc6bdecf3aa0c7091da38542d5a Mon Sep 17 00:00:00 2001
From: Jeff Bezanson <jeff.bezanson@gmail.com>
Date: Fri, 6 Jul 2012 14:13:18 -0400
Subject: [PATCH] use K-B-N summation for float arrays, with thanks to
 @JeffreySarnoff

written carefully it is no more than 20% slower
closes #199
---
 base/array.jl | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/base/array.jl b/base/array.jl
index fe6a7639c67c6..7ee9efbfaab84 100644
--- a/base/array.jl
+++ b/base/array.jl
@@ -1185,6 +1185,27 @@ function sum{T}(A::StridedArray{T})
     v
 end
 
+function sum{T<:Float}(A::StridedArray{T})
+    n = length(A)
+    if (n == 0)
+        return zero(T)
+    end
+    s = A[1]
+    c = zero(T)
+    for i in 2:n
+        Ai = A[i]
+        t = s + Ai
+        if abs(s) >= abs(Ai)
+            c += ((s-t) + Ai)
+        else
+            c += ((Ai-t) + s)
+        end
+        s = t
+    end
+
+    s + c
+end
+
 function prod{T}(A::StridedArray{T})
     if isempty(A)
         return one(T)