97 lines
2.3 KiB
V
97 lines
2.3 KiB
V
// Copyright (c) 2019-2022 Alexander Medvednikov. All rights reserved.
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// Use of this source code is governed by an MIT license
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// that can be found in the LICENSE file.
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module splitmix64
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import rand.seed
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pub const seed_len = 2
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// SplitMix64RNG ported from http://xoshiro.di.unimi.it/splitmix64.c
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pub struct SplitMix64RNG {
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mut:
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state u64 = seed.time_seed_64()
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bytes_left int
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buffer u64
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}
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// seed sets the seed of the accepting SplitMix64RNG to the given data
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// in little-endian format (i.e. lower 32 bits are in [0] and higher 32 bits in [1]).
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pub fn (mut rng SplitMix64RNG) seed(seed_data []u32) {
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if seed_data.len != 2 {
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eprintln('SplitMix64RNG needs 2 32-bit unsigned integers as the seed.')
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exit(1)
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}
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rng.state = seed_data[0] | (u64(seed_data[1]) << 32)
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rng.bytes_left = 0
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rng.buffer = 0
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}
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// byte returns a uniformly distributed pseudorandom 8-bit unsigned positive `byte`.
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[inline]
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pub fn (mut rng SplitMix64RNG) byte() byte {
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if rng.bytes_left >= 1 {
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rng.bytes_left -= 1
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value := byte(rng.buffer)
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rng.buffer >>= 8
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return value
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}
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rng.buffer = rng.u64()
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rng.bytes_left = 7
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value := byte(rng.buffer)
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rng.buffer >>= 8
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return value
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}
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// u16 returns a pseudorandom 16bit int in range `[0, 2¹⁶)`.
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[inline]
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pub fn (mut rng SplitMix64RNG) u16() u16 {
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if rng.bytes_left >= 2 {
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rng.bytes_left -= 2
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value := u16(rng.buffer)
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rng.buffer >>= 16
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return value
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}
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ans := rng.u64()
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rng.buffer = ans >> 16
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rng.bytes_left = 6
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return u16(ans)
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}
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// u32 returns a pseudorandom 32bit int in range `[0, 2³²)`.
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[inline]
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pub fn (mut rng SplitMix64RNG) u32() u32 {
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if rng.bytes_left >= 4 {
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rng.bytes_left -= 4
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value := u32(rng.buffer)
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rng.buffer >>= 32
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return value
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}
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ans := rng.u64()
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rng.buffer = ans >> 32
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rng.bytes_left = 4
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return u32(ans)
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}
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// u64 returns a pseudorandom 64bit int in range `[0, 2⁶⁴)`.
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[inline]
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pub fn (mut rng SplitMix64RNG) u64() u64 {
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rng.state += (0x9e3779b97f4a7c15)
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mut z := rng.state
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z = (z ^ (z >> u64(30))) * 0xbf58476d1ce4e5b9
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z = (z ^ (z >> u64(27))) * 0x94d049bb133111eb
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return z ^ (z >> (31))
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}
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// block_size returns the number of bits that the RNG can produce in a single iteration.
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[inline]
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pub fn (mut rng SplitMix64RNG) block_size() int {
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return 64
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}
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// free should be called when the generator is no longer needed
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[unsafe]
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pub fn (mut rng SplitMix64RNG) free() {
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unsafe { free(rng) }
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}
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