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sort: simplify rotate and reduce calls to it

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Move the checks for empty rotate changes
from the beginning of rotate to the callers.

Remove additional variable p used instead of existing m with same value.

Remove special casing of equal ranges (i==j) to exit early as no
work is saved vs checking (i!=j) and  making a single
swapRange call if this is false.

benchmark                   old ns/op      new ns/op      delta
BenchmarkStableString1K     417195         425218         +1.92%
BenchmarkStableInt1K        126661         124498         -1.71%
BenchmarkStableInt64K       10365014       10417438       +0.51%
BenchmarkStable1e2          132151         130648         -1.14%
BenchmarkStable1e4          42027428       40812649       -2.89%
BenchmarkStable1e6          8524772364     8430192391     -1.11%

Change-Id: Ia7642e9d31408496970c700f5843d53cc3ebe817
Reviewed-on: https://go-review.googlesource.com/2100
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Martin Möhrmann 2014-12-23 20:44:10 +01:00 committed by Ian Lance Taylor
parent 131758183f
commit 76cc881ef0
1 changed files with 8 additions and 16 deletions
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22
src/sort/sort.go
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@ -381,7 +381,9 @@ func symMerge(data Interface, a, m, b int) {
} }
end := n - start end := n - start
if start < m && m < end {
rotate(data, start, m, end) rotate(data, start, m, end)
}
if a < start && start < mid { if a < start && start < mid {
symMerge(data, a, start, mid) symMerge(data, a, start, mid)
} }
@ -393,32 +395,22 @@ func symMerge(data Interface, a, m, b int) {
// Rotate two consecutives blocks u = data[a:m] and v = data[m:b] in data: // Rotate two consecutives blocks u = data[a:m] and v = data[m:b] in data:
// Data of the form 'x u v y' is changed to 'x v u y'. // Data of the form 'x u v y' is changed to 'x v u y'.
// Rotate performs at most b-a many calls to data.Swap. // Rotate performs at most b-a many calls to data.Swap.
// Rotate assumes non-degenerate arguments: a < m && m < b.
func rotate(data Interface, a, m, b int) { func rotate(data Interface, a, m, b int) {
i := m - a i := m - a
if i == 0 {
return
}
j := b - m j := b - m
if j == 0 {
return
}
if i == j {
swapRange(data, a, m, i)
return
}
p := a + i
for i != j { for i != j {
if i > j { if i > j {
swapRange(data, p-i, p, j) swapRange(data, m-i, m, j)
i -= j i -= j
} else { } else {
swapRange(data, p-i, p+j-i, i) swapRange(data, m-i, m+j-i, i)
j -= i j -= i
} }
} }
swapRange(data, p-i, p, i) // i == j
swapRange(data, m-i, m, i)
} }
/* /*