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Source file test/slicecap.go

Documentation: test

     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  

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