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// 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 (
"internal/goarch"
"internal/unsafeheader"
"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 any) 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.ptrdata != 0
// Some common & small cases, without using memmove:
if hasPtr {
if size == goarch.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 := (*unsafeheader.Slice)(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, "i < s.Len")
val2 := arrayAt(s.Data, j, size, "j < s.Len")
typedmemmove(typ, tmp, val1)
typedmemmove(typ, val1, val2)
typedmemmove(typ, val2, tmp)
}
}
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