diff options
Diffstat (limited to 'libgo/go/reflect/swapper.go')
-rw-r--r-- | libgo/go/reflect/swapper.go | 74 |
1 files changed, 74 insertions, 0 deletions
diff --git a/libgo/go/reflect/swapper.go b/libgo/go/reflect/swapper.go new file mode 100644 index 0000000..5441cb0 --- /dev/null +++ b/libgo/go/reflect/swapper.go @@ -0,0 +1,74 @@ +// Copyright 2016 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package reflect + +import "unsafe" + +// Swapper returns a function that swaps the elements in the provided +// slice. +// +// Swapper panics if the provided interface is not a slice. +func Swapper(slice interface{}) func(i, j int) { + v := ValueOf(slice) + if v.Kind() != Slice { + panic(&ValueError{Method: "Swapper", Kind: v.Kind()}) + } + // Fast path for slices of size 0 and 1. Nothing to swap. + switch v.Len() { + case 0: + return func(i, j int) { panic("reflect: slice index out of range") } + case 1: + return func(i, j int) { + if i != 0 || j != 0 { + panic("reflect: slice index out of range") + } + } + } + + typ := v.Type().Elem().(*rtype) + size := typ.Size() + hasPtr := typ.kind&kindNoPointers == 0 + + // Some common & small cases, without using memmove: + if hasPtr { + if size == ptrSize { + ps := *(*[]unsafe.Pointer)(v.ptr) + return func(i, j int) { ps[i], ps[j] = ps[j], ps[i] } + } + if typ.Kind() == String { + ss := *(*[]string)(v.ptr) + return func(i, j int) { ss[i], ss[j] = ss[j], ss[i] } + } + } else { + switch size { + case 8: + is := *(*[]int64)(v.ptr) + return func(i, j int) { is[i], is[j] = is[j], is[i] } + case 4: + is := *(*[]int32)(v.ptr) + return func(i, j int) { is[i], is[j] = is[j], is[i] } + case 2: + is := *(*[]int16)(v.ptr) + return func(i, j int) { is[i], is[j] = is[j], is[i] } + case 1: + is := *(*[]int8)(v.ptr) + return func(i, j int) { is[i], is[j] = is[j], is[i] } + } + } + + s := (*sliceHeader)(v.ptr) + tmp := unsafe_New(typ) // swap scratch space + + return func(i, j int) { + if uint(i) >= uint(s.Len) || uint(j) >= uint(s.Len) { + panic("reflect: slice index out of range") + } + val1 := arrayAt(s.Data, i, size) + val2 := arrayAt(s.Data, j, size) + typedmemmove(typ, tmp, val1) + typedmemmove(typ, val1, val2) + typedmemmove(typ, val2, tmp) + } +} |