|
| 1 | +package cryptorand |
| 2 | + |
| 3 | +import ( |
| 4 | + "crypto/rand" |
| 5 | + "encoding/binary" |
| 6 | + |
| 7 | + "golang.org/x/xerrors" |
| 8 | +) |
| 9 | + |
| 10 | +// Most of this code is inspired by math/rand, so shares similar |
| 11 | +// functions and implementations, but uses crypto/rand to generate |
| 12 | +// random Int63 data. |
| 13 | + |
| 14 | +// Int64 returns a non-negative random 63-bit integer as a int64. |
| 15 | +func Int63() (int64, error) { |
| 16 | + var i int64 |
| 17 | + err := binary.Read(rand.Reader, binary.BigEndian, &i) |
| 18 | + if err != nil { |
| 19 | + return 0, xerrors.Errorf("read binary: %w", err) |
| 20 | + } |
| 21 | + |
| 22 | + if i < 0 { |
| 23 | + return -i, nil |
| 24 | + } |
| 25 | + return i, nil |
| 26 | +} |
| 27 | + |
| 28 | +// Uint64 returns a random 64-bit integer as a uint64. |
| 29 | +func Uint64() (uint64, error) { |
| 30 | + upper, err := Int63() |
| 31 | + if err != nil { |
| 32 | + return 0, xerrors.Errorf("read upper: %w", err) |
| 33 | + } |
| 34 | + |
| 35 | + lower, err := Int63() |
| 36 | + if err != nil { |
| 37 | + return 0, xerrors.Errorf("read lower: %w", err) |
| 38 | + } |
| 39 | + |
| 40 | + return uint64(lower)>>31 | uint64(upper)<<32, nil |
| 41 | +} |
| 42 | + |
| 43 | +// Int31 returns a non-negative random 31-bit integer as a int32. |
| 44 | +func Int31() (int32, error) { |
| 45 | + i, err := Int63() |
| 46 | + if err != nil { |
| 47 | + return 0, err |
| 48 | + } |
| 49 | + |
| 50 | + return int32(i >> 32), nil |
| 51 | +} |
| 52 | + |
| 53 | +// Uint32 returns a 32-bit value as a uint32. |
| 54 | +func Uint32() (uint32, error) { |
| 55 | + i, err := Int63() |
| 56 | + if err != nil { |
| 57 | + return 0, err |
| 58 | + } |
| 59 | + |
| 60 | + return uint32(i >> 31), nil |
| 61 | +} |
| 62 | + |
| 63 | +// Int returns a non-negative random integer as a int. |
| 64 | +func Int() (int, error) { |
| 65 | + i, err := Int63() |
| 66 | + if err != nil { |
| 67 | + return 0, err |
| 68 | + } |
| 69 | + |
| 70 | + if i < 0 { |
| 71 | + return int(-i), nil |
| 72 | + } |
| 73 | + return int(i), nil |
| 74 | +} |
| 75 | + |
| 76 | +// Int63n returns a non-negative random integer in [0,n) as a int64. |
| 77 | +func Int63n(n int64) (int64, error) { |
| 78 | + if n <= 0 { |
| 79 | + panic("invalid argument to Int63n") |
| 80 | + } |
| 81 | + |
| 82 | + max := int64((1 << 63) - 1 - (1<<63)%uint64(n)) |
| 83 | + i, err := Int63() |
| 84 | + if err != nil { |
| 85 | + return 0, err |
| 86 | + } |
| 87 | + |
| 88 | + for i > max { |
| 89 | + i, err = Int63() |
| 90 | + if err != nil { |
| 91 | + return 0, err |
| 92 | + } |
| 93 | + } |
| 94 | + |
| 95 | + return i % n, nil |
| 96 | +} |
| 97 | + |
| 98 | +// Int31n returns a non-negative integer in [0,n) as a int32. |
| 99 | +func Int31n(n int32) (int32, error) { |
| 100 | + i, err := Uint32() |
| 101 | + if err != nil { |
| 102 | + return 0, err |
| 103 | + } |
| 104 | + |
| 105 | + return UnbiasedModulo32(i, n) |
| 106 | +} |
| 107 | + |
| 108 | +// UnbiasedModulo32 uniformly modulos v by n over a sufficiently large data |
| 109 | +// set, regenerating v if necessary. n must be > 0. All input bits in v must be |
| 110 | +// fully random, you cannot cast a random uint8/uint16 for input into this |
| 111 | +// function. |
| 112 | +func UnbiasedModulo32(v uint32, n int32) (int32, error) { |
| 113 | + prod := uint64(v) * uint64(n) |
| 114 | + low := uint32(prod) |
| 115 | + if low < uint32(n) { |
| 116 | + thresh := uint32(-n) % uint32(n) |
| 117 | + for low < thresh { |
| 118 | + var err error |
| 119 | + v, err = Uint32() |
| 120 | + if err != nil { |
| 121 | + return 0, err |
| 122 | + } |
| 123 | + prod = uint64(v) * uint64(n) |
| 124 | + low = uint32(prod) |
| 125 | + } |
| 126 | + } |
| 127 | + return int32(prod >> 32), nil |
| 128 | +} |
| 129 | + |
| 130 | +// Intn returns a non-negative integer in [0,n) as a int. |
| 131 | +func Intn(n int) (int, error) { |
| 132 | + if n <= 0 { |
| 133 | + panic("n must be a positive nonzero number") |
| 134 | + } |
| 135 | + |
| 136 | + if n <= 1<<31-1 { |
| 137 | + i, err := Int31n(int32(n)) |
| 138 | + if err != nil { |
| 139 | + return 0, err |
| 140 | + } |
| 141 | + |
| 142 | + return int(i), nil |
| 143 | + } |
| 144 | + |
| 145 | + i, err := Int63n(int64(n)) |
| 146 | + if err != nil { |
| 147 | + return 0, err |
| 148 | + } |
| 149 | + |
| 150 | + return int(i), nil |
| 151 | +} |
| 152 | + |
| 153 | +// Float64 returns a random number in [0.0,1.0) as a float64. |
| 154 | +func Float64() (float64, error) { |
| 155 | +again: |
| 156 | + i, err := Int63n(1 << 53) |
| 157 | + if err != nil { |
| 158 | + return 0, err |
| 159 | + } |
| 160 | + |
| 161 | + f := (float64(i) / (1 << 53)) |
| 162 | + if f == 1 { |
| 163 | + goto again |
| 164 | + } |
| 165 | + |
| 166 | + return f, nil |
| 167 | +} |
| 168 | + |
| 169 | +// Float32 returns a random number in [0.0,1.0) as a float32. |
| 170 | +func Float32() (float32, error) { |
| 171 | +again: |
| 172 | + i, err := Float64() |
| 173 | + if err != nil { |
| 174 | + return 0, err |
| 175 | + } |
| 176 | + |
| 177 | + f := float32(i) |
| 178 | + if f == 1 { |
| 179 | + goto again |
| 180 | + } |
| 181 | + |
| 182 | + return f, nil |
| 183 | +} |
| 184 | + |
| 185 | +// Bool returns a random true/false value as a bool. |
| 186 | +func Bool() (bool, error) { |
| 187 | + i, err := Uint64() |
| 188 | + if err != nil { |
| 189 | + return false, err |
| 190 | + } |
| 191 | + |
| 192 | + // True if the least significant bit is 1 |
| 193 | + return i&1 == 1, nil |
| 194 | +} |
0 commit comments