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