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Diffstat (limited to '')
-rw-r--r-- | dependencies/pkg/mod/golang.org/x/exp@v0.0.0-20220613132600-b0d781184e0d/rand/rng.go | 91 |
1 files changed, 91 insertions, 0 deletions
diff --git a/dependencies/pkg/mod/golang.org/x/exp@v0.0.0-20220613132600-b0d781184e0d/rand/rng.go b/dependencies/pkg/mod/golang.org/x/exp@v0.0.0-20220613132600-b0d781184e0d/rand/rng.go new file mode 100644 index 0000000..9b79108 --- /dev/null +++ b/dependencies/pkg/mod/golang.org/x/exp@v0.0.0-20220613132600-b0d781184e0d/rand/rng.go @@ -0,0 +1,91 @@ +// Copyright 2017 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package rand + +import ( + "encoding/binary" + "io" + "math/bits" +) + +// PCGSource is an implementation of a 64-bit permuted congruential +// generator as defined in +// +// PCG: A Family of Simple Fast Space-Efficient Statistically Good +// Algorithms for Random Number Generation +// Melissa E. O’Neill, Harvey Mudd College +// http://www.pcg-random.org/pdf/toms-oneill-pcg-family-v1.02.pdf +// +// The generator here is the congruential generator PCG XSL RR 128/64 (LCG) +// as found in the software available at http://www.pcg-random.org/. +// It has period 2^128 with 128 bits of state, producing 64-bit values. +// Is state is represented by two uint64 words. +type PCGSource struct { + low uint64 + high uint64 +} + +const ( + maxUint32 = (1 << 32) - 1 + + multiplier = 47026247687942121848144207491837523525 + mulHigh = multiplier >> 64 + mulLow = multiplier & maxUint64 + + increment = 117397592171526113268558934119004209487 + incHigh = increment >> 64 + incLow = increment & maxUint64 + + // TODO: Use these? + initializer = 245720598905631564143578724636268694099 + initHigh = initializer >> 64 + initLow = initializer & maxUint64 +) + +// Seed uses the provided seed value to initialize the generator to a deterministic state. +func (pcg *PCGSource) Seed(seed uint64) { + pcg.low = seed + pcg.high = seed // TODO: What is right? +} + +// Uint64 returns a pseudo-random 64-bit unsigned integer as a uint64. +func (pcg *PCGSource) Uint64() uint64 { + pcg.multiply() + pcg.add() + // XOR high and low 64 bits together and rotate right by high 6 bits of state. + return bits.RotateLeft64(pcg.high^pcg.low, -int(pcg.high>>58)) +} + +func (pcg *PCGSource) add() { + var carry uint64 + pcg.low, carry = bits.Add64(pcg.low, incLow, 0) + pcg.high, _ = bits.Add64(pcg.high, incHigh, carry) +} + +func (pcg *PCGSource) multiply() { + hi, lo := bits.Mul64(pcg.low, mulLow) + hi += pcg.high * mulLow + hi += pcg.low * mulHigh + pcg.low = lo + pcg.high = hi +} + +// MarshalBinary returns the binary representation of the current state of the generator. +func (pcg *PCGSource) MarshalBinary() ([]byte, error) { + var buf [16]byte + binary.BigEndian.PutUint64(buf[:8], pcg.high) + binary.BigEndian.PutUint64(buf[8:], pcg.low) + return buf[:], nil +} + +// UnmarshalBinary sets the state of the generator to the state represented in data. +func (pcg *PCGSource) UnmarshalBinary(data []byte) error { + if len(data) < 16 { + return io.ErrUnexpectedEOF + } + pcg.low = binary.BigEndian.Uint64(data[8:]) + pcg.high = binary.BigEndian.Uint64(data[:8]) + return nil +} |