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107 lines
2.8 KiB
Go
107 lines
2.8 KiB
Go
// 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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// +build !ppc64,!ppc64le,!arm64,!mips,!mipsle,!mips64,!mips64le
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// +build !js,!appengine,!safe
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package reflectutil
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import (
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"reflect"
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"unsafe"
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)
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const ptrSize = 4 << (^uintptr(0) >> 63) // unsafe.Sizeof(uintptr(0)) but an ideal const
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// arrayAt returns the i-th element of p, a C-array whose elements are
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// eltSize wide (in bytes).
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func arrayAt(p unsafe.Pointer, i int, eltSize uintptr) unsafe.Pointer {
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return unsafe.Pointer(uintptr(p) + uintptr(i)*eltSize)
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}
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type sliceHeader struct {
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Data unsafe.Pointer
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Len int
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Cap int
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}
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func swapper(v reflect.Value) func(i, j int) {
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maxLen := uint(v.Len())
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s := sliceHeader{unsafe.Pointer(v.Pointer()), int(maxLen), int(maxLen)}
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tt := v.Type()
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elemt := tt.Elem()
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typ := unsafe.Pointer(reflect.ValueOf(elemt).Pointer())
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size := elemt.Size()
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hasPtr := hasPointers(elemt)
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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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var ps []unsafe.Pointer
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*(*sliceHeader)(unsafe.Pointer(&ps)) = s
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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 elemt.Kind() == reflect.String {
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var ss []string
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*(*sliceHeader)(unsafe.Pointer(&ss)) = s
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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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var is []int64
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*(*sliceHeader)(unsafe.Pointer(&is)) = s
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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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var is []int32
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*(*sliceHeader)(unsafe.Pointer(&is)) = s
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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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var is []int16
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*(*sliceHeader)(unsafe.Pointer(&is)) = s
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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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var is []int8
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*(*sliceHeader)(unsafe.Pointer(&is)) = s
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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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// Allocate scratch space for swaps:
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tmpVal := reflect.New(elemt)
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tmp := unsafe.Pointer(tmpVal.Pointer())
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// If no pointers (or Go 1.4 or below), we don't require typedmemmove:
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if !haveTypedMemmove || !hasPtr {
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return func(i, j int) {
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if uint(i) >= maxLen || uint(j) >= maxLen {
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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)
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val2 := arrayAt(s.Data, j, size)
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memmove(tmp, val1, size)
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memmove(val1, val2, size)
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memmove(val2, tmp, size)
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}
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}
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return func(i, j int) {
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if uint(i) >= maxLen || uint(j) >= maxLen {
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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)
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val2 := arrayAt(s.Data, j, size)
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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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// memmove copies size bytes from src to dst.
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// The memory must not contain any pointers.
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//go:noescape
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func memmove(dst, src unsafe.Pointer, size uintptr)
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