fe_alias_test.go

     1  // Copyright (c) 2019 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package field
     6  
     7  import (
     8  	"testing"
     9  	"testing/quick"
    10  )
    11  
    12  func checkAliasingOneArg(f func(v, x *Element) *Element) func(v, x Element) bool {
    13  	return func(v, x Element) bool {
    14  		x1, v1 := x, x
    15  
    16  		// Calculate a reference f(x) without aliasing.
    17  		if out := f(&v, &x); out != &v && isInBounds(out) {
    18  			return false
    19  		}
    20  
    21  		// Test aliasing the argument and the receiver.
    22  		if out := f(&v1, &v1); out != &v1 || v1 != v {
    23  			return false
    24  		}
    25  
    26  		// Ensure the arguments was not modified.
    27  		return x == x1
    28  	}
    29  }
    30  
    31  func checkAliasingTwoArgs(f func(v, x, y *Element) *Element) func(v, x, y Element) bool {
    32  	return func(v, x, y Element) bool {
    33  		x1, y1, v1 := x, y, Element{}
    34  
    35  		// Calculate a reference f(x, y) without aliasing.
    36  		if out := f(&v, &x, &y); out != &v && isInBounds(out) {
    37  			return false
    38  		}
    39  
    40  		// Test aliasing the first argument and the receiver.
    41  		v1 = x
    42  		if out := f(&v1, &v1, &y); out != &v1 || v1 != v {
    43  			return false
    44  		}
    45  		// Test aliasing the second argument and the receiver.
    46  		v1 = y
    47  		if out := f(&v1, &x, &v1); out != &v1 || v1 != v {
    48  			return false
    49  		}
    50  
    51  		// Calculate a reference f(x, x) without aliasing.
    52  		if out := f(&v, &x, &x); out != &v {
    53  			return false
    54  		}
    55  
    56  		// Test aliasing the first argument and the receiver.
    57  		v1 = x
    58  		if out := f(&v1, &v1, &x); out != &v1 || v1 != v {
    59  			return false
    60  		}
    61  		// Test aliasing the second argument and the receiver.
    62  		v1 = x
    63  		if out := f(&v1, &x, &v1); out != &v1 || v1 != v {
    64  			return false
    65  		}
    66  		// Test aliasing both arguments and the receiver.
    67  		v1 = x
    68  		if out := f(&v1, &v1, &v1); out != &v1 || v1 != v {
    69  			return false
    70  		}
    71  
    72  		// Ensure the arguments were not modified.
    73  		return x == x1 && y == y1
    74  	}
    75  }
    76  
    77  // TestAliasing checks that receivers and arguments can alias each other without
    78  // leading to incorrect results. That is, it ensures that it's safe to write
    79  //
    80  //     v.Invert(v)
    81  //
    82  // or
    83  //
    84  //     v.Add(v, v)
    85  //
    86  // without any of the inputs getting clobbered by the output being written.
    87  func TestAliasing(t *testing.T) {
    88  	type target struct {
    89  		name     string
    90  		oneArgF  func(v, x *Element) *Element
    91  		twoArgsF func(v, x, y *Element) *Element
    92  	}
    93  	for _, tt := range []target{
    94  		{name: "Absolute", oneArgF: (*Element).Absolute},
    95  		{name: "Invert", oneArgF: (*Element).Invert},
    96  		{name: "Negate", oneArgF: (*Element).Negate},
    97  		{name: "Set", oneArgF: (*Element).Set},
    98  		{name: "Square", oneArgF: (*Element).Square},
    99  		{name: "Multiply", twoArgsF: (*Element).Multiply},
   100  		{name: "Add", twoArgsF: (*Element).Add},
   101  		{name: "Subtract", twoArgsF: (*Element).Subtract},
   102  		{
   103  			name: "Select0",
   104  			twoArgsF: func(v, x, y *Element) *Element {
   105  				return (*Element).Select(v, x, y, 0)
   106  			},
   107  		},
   108  		{
   109  			name: "Select1",
   110  			twoArgsF: func(v, x, y *Element) *Element {
   111  				return (*Element).Select(v, x, y, 1)
   112  			},
   113  		},
   114  	} {
   115  		var err error
   116  		switch {
   117  		case tt.oneArgF != nil:
   118  			err = quick.Check(checkAliasingOneArg(tt.oneArgF), &quick.Config{MaxCountScale: 1 << 8})
   119  		case tt.twoArgsF != nil:
   120  			err = quick.Check(checkAliasingTwoArgs(tt.twoArgsF), &quick.Config{MaxCountScale: 1 << 8})
   121  		}
   122  		if err != nil {
   123  			t.Errorf("%v: %v", tt.name, err)
   124  		}
   125  	}
   126  }
   127
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