From ccd992355df7192993c666236047820244914598 Mon Sep 17 00:00:00 2001
From: Daniel Baumann <daniel.baumann@progress-linux.org>
Date: Tue, 16 Apr 2024 21:19:13 +0200
Subject: Adding upstream version 1.21.8.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
---
 src/internal/reflectlite/swapper.go | 78 +++++++++++++++++++++++++++++++++++++
 1 file changed, 78 insertions(+)
 create mode 100644 src/internal/reflectlite/swapper.go

(limited to 'src/internal/reflectlite/swapper.go')

diff --git a/src/internal/reflectlite/swapper.go b/src/internal/reflectlite/swapper.go
new file mode 100644
index 0000000..ac17d9b
--- /dev/null
+++ b/src/internal/reflectlite/swapper.go
@@ -0,0 +1,78 @@
+// 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 reflectlite
+
+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().common()
+	size := typ.Size()
+	hasPtr := typ.PtrBytes != 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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