use K-B-N summation for float arrays, with thanks to @JeffreySarnoff

written carefully it is no more than 20% slower closes #199
JuliaLang · Jul 6, 2012 · 19ff52a · 19ff52a · StefanKarpinski · Jul 6, 2012
1 parent a408bcc
commit 19ff52a
Showing 1 changed file with 21 additions and 0 deletions.
diff --git 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)