sort: deduplicate inner loop of Stable

benchmark                   old ns/op      new ns/op      delta
BenchmarkStableInt1K        117212         116287         -0.79%
BenchmarkStableInt64K       9632002        9587872        -0.46%
BenchmarkStable1e4          40044309       39865644       -0.45%
BenchmarkStable1e2          126985         126456         -0.42%
BenchmarkStableString1K     389774         391052         +0.33%
BenchmarkStable1e6          8183202516     8157693442     -0.31%

Change-Id: I14e518ad49ecce3d1fc2b056e1acd5e5a2de8144
Reviewed-on: https://go-review.googlesource.com/1821
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

diff --git a/src/sort/sort.go b/src/sort/sort.go
index e980c295c32f61b8bafdf9761943ea71d5554989..63f8894a1967cd42ddfd757e52221143521aac24 100644 (file)
--- a/src/sort/sort.go
+++ b/src/sort/sort.go
@@ -359,30 +359,25 @@ func symMerge(data Interface, a, m, b int) {
 
        mid := a + (b-a)/2
        n := mid + m
-       start := 0
+       var start, r int
        if m > mid {
                start = n - b
-               r, p := mid, n-1
-               for start < r {
-                       c := start + (r-start)/2
-                       if !data.Less(p-c, c) {
-                               start = c + 1
-                       } else {
-                               r = c
-                       }
-               }
+               r = mid
        } else {
                start = a
-               r, p := m, n-1
-               for start < r {
-                       c := start + (r-start)/2
-                       if !data.Less(p-c, c) {
-                               start = c + 1
-                       } else {
-                               r = c
-                       }
+               r = m
+       }
+       p := n - 1
+
+       for start < r {
+               c := start + (r-start)/2
+               if !data.Less(p-c, c) {
+                       start = c + 1
+               } else {
+                       r = c
                }
        }
+
        end := n - start
        rotate(data, start, m, end)
        symMerge(data, a, start, mid)