29 lines
772 B
Go
29 lines
772 B
Go
// Package random implements the XORShift PRNG and a way to derive random state
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// from an AnnounceRequest.
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package random
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// GenerateAndAdvance applies XORShift128Plus on s0 and s1, returning
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// the new states newS0, newS1 and a pseudo-random number v.
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func GenerateAndAdvance(s0, s1 uint64) (v, newS0, newS1 uint64) {
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v = s0 + s1
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newS0 = s1
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s0 ^= (s0 << 23)
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newS1 = s0 ^ s1 ^ (s0 >> 18) ^ (s1 >> 5)
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return
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}
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// Intn generates an int k that satisfies k >= 0 && k < n.
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// n must be > 0.
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// It returns the generated k and the new state of the generator.
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func Intn(s0, s1 uint64, n int) (int, uint64, uint64) {
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if n <= 0 {
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panic("invalid n <= 0")
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}
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v, newS0, newS1 := GenerateAndAdvance(s0, s1)
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k := int(v)
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if k < 0 {
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k = -k
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}
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return k % n, newS0, newS1
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}
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