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v/vlib/rand/wyrand/wyrand.v
2022-04-15 18:25:45 +03:00

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// Copyright (c) 2019-2022 Alexander Medvednikov. All rights reserved.
// Use of this source code is governed by an MIT license
// that can be found in the LICENSE file.
module wyrand
import hash
import rand.seed
// Redefinition of some constants that we will need for pseudorandom number generation.
const (
wyp0 = u64(0xa0761d6478bd642f)
wyp1 = u64(0xe7037ed1a0b428db)
)
pub const seed_len = 2
// WyRandRNG is a RNG based on the WyHash hashing algorithm.
pub struct WyRandRNG {
mut:
state u64 = seed.time_seed_64()
bytes_left int
buffer u64
}
// seed sets the seed, needs only two `u32`s in little-endian format as [lower, higher].
pub fn (mut rng WyRandRNG) seed(seed_data []u32) {
if seed_data.len != 2 {
eprintln('WyRandRNG needs 2 32-bit unsigned integers as the seed.')
exit(1)
}
rng.state = seed_data[0] | (u64(seed_data[1]) << 32)
rng.bytes_left = 0
rng.buffer = 0
}
// byte returns a uniformly distributed pseudorandom 8-bit unsigned positive `byte`.
[inline]
pub fn (mut rng WyRandRNG) u8() u8 {
// Can we extract a value from the buffer?
if rng.bytes_left >= 1 {
rng.bytes_left -= 1
value := u8(rng.buffer)
rng.buffer >>= 8
return value
}
// Add a new value to the buffer
rng.buffer = rng.u64()
rng.bytes_left = 7
value := u8(rng.buffer)
rng.buffer >>= 8
return value
}
// u16 returns a pseudorandom 16bit int in range `[0, 2¹⁶)`.
[inline]
pub fn (mut rng WyRandRNG) u16() u16 {
if rng.bytes_left >= 2 {
rng.bytes_left -= 2
value := u16(rng.buffer)
rng.buffer >>= 16
return value
}
ans := rng.u64()
rng.buffer = ans >> 16
rng.bytes_left = 6
return u16(ans)
}
// u32 returns a pseudorandom 32bit int in range `[0, 2³²)`.
[inline]
pub fn (mut rng WyRandRNG) u32() u32 {
if rng.bytes_left >= 4 {
rng.bytes_left -= 4
value := u32(rng.buffer)
rng.buffer >>= 32
return value
}
ans := rng.u64()
rng.buffer = ans >> 32
rng.bytes_left = 4
return u32(ans)
}
// u64 returns a pseudorandom 64bit int in range `[0, 2⁶⁴)`.
[inline]
pub fn (mut rng WyRandRNG) u64() u64 {
unsafe {
mut seed1 := rng.state
seed1 += wyrand.wyp0
rng.state = seed1
return hash.wymum(seed1 ^ wyrand.wyp1, seed1)
}
return 0
}
// block_size returns the number of bits that the RNG can produce in a single iteration.
[inline]
pub fn (mut rng WyRandRNG) block_size() int {
return 64
}