qbit/go
1
0
Fork 0
mirror of https://github.com/golang/go synced 2024-11-23 00:30:07 -07:00
Code Releases Activity

slices: amortize allocations in Insert

Browse Source 
Fixes #54948

Change-Id: I467afb940b539b100dcce687b05914a9da7b9ed2
Reviewed-on: https://go-review.googlesource.com/c/go/+/484159
Run-TryBot: Ian Lance Taylor <iant@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Valentin Deleplace <deleplace@google.com>
This commit is contained in:
Ian Lance Taylor 2023-04-12 13:57:21 -07:00 committed by Gopher Robot
parent 74c296b69f
commit 3de5b4da26
2 changed files with 19 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
src/slices/slices.go
View File

@ -88,7 +88,11 @@ func Insert[S ~[]E, E any](s S, i int, v ...E) S {
copy(s2[i:], v)
return s2
}
s2 := make(S, tot)
// Use append rather than make so that we bump the size of
// the slice up to the next storage class.
// This is what Grow does but we don't call Grow because
// that might copy the values twice.
s2 := append(S(nil), make(S, tot)...)
copy(s2, s[:i])
copy(s2[i:], v)
copy(s2[i+len(v):], s[i:])

14
src/slices/slices_test.go
View File

@ -256,6 +256,20 @@ func TestInsert(t *testing.T) {
t.Errorf("Insert(%v, %d, %v...) = %v, want %v", test.s, test.i, test.add, got, test.want)
}
}
if !testenv.OptimizationOff() && !race.Enabled {
// Allocations should be amortized.
const count = 50
n := testing.AllocsPerRun(10, func() {
s := []int{1, 2, 3}
for i := 0; i < count; i++ {
s = Insert(s, 0, 1)
}
})
if n > count/2 {
t.Errorf("too many allocations inserting %d elements: got %v, want less than %d", count, n, count/2)
}
}
}
var deleteTests = []struct {