43 lines
1.1 KiB
V
43 lines
1.1 KiB
V
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module rand
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// Ported from http://xoshiro.di.unimi.it/splitmix64.c
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struct Splitmix64 {
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mut:
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state u64
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}
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/**
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* new_splitmix64 - a Splitmix64 PRNG generator
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* @param seed the initial seed of the PRNG.
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* @return a new Splitmix64 PRNG instance
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*/
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pub fn new_splitmix64(seed u64) Splitmix64 {
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return Splitmix64{ seed }
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}
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/**
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* Splitmix64.next - update the PRNG state and get back the next random number
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* @return the generated pseudo random number
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*/
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[inline] pub fn (rng mut Splitmix64) next() u64 {
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rng.state += u64(0x9e3779b97f4a7c15)
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mut z := rng.state
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z = (z ^ u64((z >> u64(30)))) * u64(0xbf58476d1ce4e5b9)
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z = (z ^ u64((z >> u64(27)))) * u64(0x94d049bb133111eb)
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return z ^ u64(z >> u64(31))
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}
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/**
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* Splitmix64.bounded_next - Get the next random number < bound
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* @param bound - the returned random number will be < bound
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* @return the generated pseudo random number
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*/
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[inline] pub fn (rng mut Splitmix64) bounded_next(bound u64) u64 {
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threshold := u64( -bound % bound )
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for {
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r := rng.next()
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if r >= threshold {
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return u64( r % bound )
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}
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}
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return u64(0)
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}
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