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# Source file src/crypto/rand/util_test.go

## Documentation: crypto/rand

```     1  // Copyright 2013 The Go Authors. All rights reserved.
2  // Use of this source code is governed by a BSD-style
4
5  package rand_test
6
7  import (
8  	"bytes"
9  	"crypto/rand"
10  	"fmt"
11  	"io"
12  	"math/big"
13  	mathrand "math/rand"
14  	"testing"
15  	"time"
16  )
17
18  // https://golang.org/issue/6849.
19  func TestPrimeSmall(t *testing.T) {
20  	for n := 2; n < 10; n++ {
21  		p, err := rand.Prime(rand.Reader, n)
22  		if err != nil {
23  			t.Fatalf("Can't generate %d-bit prime: %v", n, err)
24  		}
25  		if p.BitLen() != n {
26  			t.Fatalf("%v is not %d-bit", p, n)
27  		}
28  		if !p.ProbablyPrime(32) {
29  			t.Fatalf("%v is not prime", p)
30  		}
31  	}
32  }
33
34  // Test that passing bits < 2 causes Prime to return nil, error
35  func TestPrimeBitsLt2(t *testing.T) {
36  	if p, err := rand.Prime(rand.Reader, 1); p != nil || err == nil {
37  		t.Errorf("Prime should return nil, error when called with bits < 2")
38  	}
39  }
40
41  func TestInt(t *testing.T) {
42  	// start at 128 so the case of (max.BitLen() % 8) == 0 is covered
43  	for n := 128; n < 140; n++ {
44  		b := new(big.Int).SetInt64(int64(n))
45  		if i, err := rand.Int(rand.Reader, b); err != nil {
46  			t.Fatalf("Can't generate random value: %v, %v", i, err)
47  		}
48  	}
49  }
50
53  	n int
54  }
55
58  	r.n += n
59  	return n, err
60  }
61
62  // Test that Int reads only the necessary number of bytes from the reader for
63  // max at each bit length
65  	for i := 0; i < 32; i++ {
66  		max := int64(1 << uint64(i))
67  		t.Run(fmt.Sprintf("max=%d", max), func(t *testing.T) {
69
70  			_, err := rand.Int(reader, big.NewInt(max))
71  			if err != nil {
72  				t.Fatalf("Can't generate random value: %d, %v", max, err)
73  			}
74  			expected := (i + 7) / 8
75  			if reader.n != expected {
77  			}
78  		})
79  	}
80  }
81
82  // Test that Int does not mask out valid return values
84  	for max := 1; max <= 256; max++ {
85  		t.Run(fmt.Sprintf("max=%d", max), func(t *testing.T) {
86  			for i := 0; i < max; i++ {
87  				var b bytes.Buffer
88  				b.WriteByte(byte(i))
89  				n, err := rand.Int(&b, big.NewInt(int64(max)))
90  				if err != nil {
91  					t.Fatalf("Can't generate random value: %d, %v", max, err)
92  				}
93  				if n.Int64() != int64(i) {
94  					t.Errorf("Int(reader, %d) should have returned value of %d, but it returned: %v", max, i, n)
95  				}
96  			}
97  		})
98  	}
99  }
100
101  func testIntPanics(t *testing.T, b *big.Int) {
102  	defer func() {
103  		if err := recover(); err == nil {
104  			t.Errorf("Int should panic when called with max <= 0: %v", b)
105  		}
106  	}()
108  }
109
110  // Test that passing a new big.Int as max causes Int to panic
111  func TestIntEmptyMaxPanics(t *testing.T) {
112  	b := new(big.Int)
113  	testIntPanics(t, b)
114  }
115
116  // Test that passing a negative value as max causes Int to panic
117  func TestIntNegativeMaxPanics(t *testing.T) {
118  	b := new(big.Int).SetInt64(int64(-1))
119  	testIntPanics(t, b)
120  }
121
122  func BenchmarkPrime(b *testing.B) {
123  	r := mathrand.New(mathrand.NewSource(time.Now().UnixNano()))
124  	for i := 0; i < b.N; i++ {
125  		rand.Prime(r, 1024)
126  	}
127  }
128
```

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