go slicecap 源码
golang slicecap 代码
文件路径：/test/slicecap.go
// run
// Copyright 2014 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 main
import "unsafe"
var (
hello = "hello"
bytes = []byte{1, 2, 3, 4, 5}
ints = []int32{1, 2, 3, 4, 5}
five = 5
ok = true
)
func notOK() {
if ok {
println("BUG:")
ok = false
}
}
func checkString(desc, s string) {
p1 := *(*uintptr)(unsafe.Pointer(&s))
p2 := *(*uintptr)(unsafe.Pointer(&hello))
if p1-p2 >= 5 {
notOK()
println("string", desc, "has invalid base")
}
}
func checkBytes(desc string, s []byte) {
p1 := *(*uintptr)(unsafe.Pointer(&s))
p2 := *(*uintptr)(unsafe.Pointer(&bytes))
if p1-p2 >= 5 {
println("byte slice", desc, "has invalid base")
}
}
func checkInts(desc string, s []int32) {
p1 := *(*uintptr)(unsafe.Pointer(&s))
p2 := *(*uintptr)(unsafe.Pointer(&ints))
if p1-p2 >= 5*4 {
println("int slice", desc, "has invalid base")
}
}
func main() {
{
x := hello
checkString("x", x)
checkString("x[5:]", x[5:])
checkString("x[five:]", x[five:])
checkString("x[5:five]", x[5:five])
checkString("x[five:5]", x[five:5])
checkString("x[five:five]", x[five:five])
checkString("x[1:][2:][2:]", x[1:][2:][2:])
y := x[4:]
checkString("y[1:]", y[1:])
}
{
x := bytes
checkBytes("x", x)
checkBytes("x[5:]", x[5:])
checkBytes("x[five:]", x[five:])
checkBytes("x[5:five]", x[5:five])
checkBytes("x[five:5]", x[five:5])
checkBytes("x[five:five]", x[five:five])
checkBytes("x[1:][2:][2:]", x[1:][2:][2:])
y := x[4:]
checkBytes("y[1:]", y[1:])
}
{
x := ints
checkInts("x", x)
checkInts("x[5:]", x[5:])
checkInts("x[five:]", x[five:])
checkInts("x[5:five]", x[5:five])
checkInts("x[five:5]", x[five:5])
checkInts("x[five:five]", x[five:five])
checkInts("x[1:][2:][2:]", x[1:][2:][2:])
y := x[4:]
checkInts("y[1:]", y[1:])
}
}
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