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      1 // run
      2 
      3 // Copyright 2014 The Go Authors. All rights reserved.
      4 // Use of this source code is governed by a BSD-style
      5 // license that can be found in the LICENSE file.
      6 
      7 package main
      8 
      9 import "unsafe"
     10 
     11 var (
     12 	hello = "hello"
     13 	bytes = []byte{1, 2, 3, 4, 5}
     14 	ints  = []int32{1, 2, 3, 4, 5}
     15 
     16 	five = 5
     17 
     18 	ok = true
     19 )
     20 
     21 func notOK() {
     22 	if ok {
     23 		println("BUG:")
     24 		ok = false
     25 	}
     26 }
     27 
     28 func checkString(desc, s string) {
     29 	p1 := *(*uintptr)(unsafe.Pointer(&s))
     30 	p2 := *(*uintptr)(unsafe.Pointer(&hello))
     31 	if p1-p2 >= 5 {
     32 		notOK()
     33 		println("string", desc, "has invalid base")
     34 	}
     35 }
     36 
     37 func checkBytes(desc string, s []byte) {
     38 	p1 := *(*uintptr)(unsafe.Pointer(&s))
     39 	p2 := *(*uintptr)(unsafe.Pointer(&bytes))
     40 	if p1-p2 >= 5 {
     41 		println("byte slice", desc, "has invalid base")
     42 	}
     43 }
     44 
     45 func checkInts(desc string, s []int32) {
     46 	p1 := *(*uintptr)(unsafe.Pointer(&s))
     47 	p2 := *(*uintptr)(unsafe.Pointer(&ints))
     48 	if p1-p2 >= 5*4 {
     49 		println("int slice", desc, "has invalid base")
     50 	}
     51 }
     52 
     53 func main() {
     54 	{
     55 		x := hello
     56 		checkString("x", x)
     57 		checkString("x[5:]", x[5:])
     58 		checkString("x[five:]", x[five:])
     59 		checkString("x[5:five]", x[5:five])
     60 		checkString("x[five:5]", x[five:5])
     61 		checkString("x[five:five]", x[five:five])
     62 		checkString("x[1:][2:][2:]", x[1:][2:][2:])
     63 		y := x[4:]
     64 		checkString("y[1:]", y[1:])
     65 	}
     66 	{
     67 		x := bytes
     68 		checkBytes("x", x)
     69 		checkBytes("x[5:]", x[5:])
     70 		checkBytes("x[five:]", x[five:])
     71 		checkBytes("x[5:five]", x[5:five])
     72 		checkBytes("x[five:5]", x[five:5])
     73 		checkBytes("x[five:five]", x[five:five])
     74 		checkBytes("x[1:][2:][2:]", x[1:][2:][2:])
     75 		y := x[4:]
     76 		checkBytes("y[1:]", y[1:])
     77 	}
     78 	{
     79 		x := ints
     80 		checkInts("x", x)
     81 		checkInts("x[5:]", x[5:])
     82 		checkInts("x[five:]", x[five:])
     83 		checkInts("x[5:five]", x[5:five])
     84 		checkInts("x[five:5]", x[five:5])
     85 		checkInts("x[five:five]", x[five:five])
     86 		checkInts("x[1:][2:][2:]", x[1:][2:][2:])
     87 		y := x[4:]
     88 		checkInts("y[1:]", y[1:])
     89 	}
     90 }
     91