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// Copyright (c) 2019-2021 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 pcg32
import rand.seed
import rand.constants
// PCG32RNG ported from http://www.pcg-random.org/download.html,
// https://github.com/imneme/pcg-c-basic/blob/master/pcg_basic.c, and
// https://github.com/imneme/pcg-c-basic/blob/master/pcg_basic.h
pub struct PCG32RNG {
mut:
state u64 = u64(0x853c49e6748fea9b) ^ seed.time_seed_64()
inc u64 = u64(0xda3e39cb94b95bdb) ^ seed.time_seed_64()
}
// seed seeds the PCG32RNG with 4 `u32` values.
// The first 2 represent the 64-bit initial state as `[lower 32 bits, higher 32 bits]`
// The last 2 represent the 64-bit stream/step of the PRNG.
pub fn (mut rng PCG32RNG) seed(seed_data []u32) {
if seed_data.len != 4 {
eprintln('PCG32RNG needs 4 u32s to be seeded. First two the initial state and the last two the stream/step. Both in little endian format: [lower, higher].')
exit(1)
}
init_state := u64(seed_data[0]) | (u64(seed_data[1]) << 32)
init_seq := u64(seed_data[2]) | (u64(seed_data[3]) << 32)
rng.state = u64(0)
rng.inc = (init_seq << u64(1)) | u64(1)
rng.u32()
rng.state += init_state
rng.u32()
}
// u32 returns a pseudorandom unsigned `u32`.
[inline]
pub fn (mut rng PCG32RNG) u32() u32 {
oldstate := rng.state
rng.state = oldstate * (6364136223846793005) + rng.inc
xorshifted := u32(((oldstate >> u64(18)) ^ oldstate) >> u64(27))
rot := u32(oldstate >> u64(59))
return ((xorshifted >> rot) | (xorshifted << ((-rot) & u32(31))))
}
// u64 returns a pseudorandom 64-bit unsigned `u64`.
[inline]
pub fn (mut rng PCG32RNG) u64() u64 {
return u64(rng.u32()) | (u64(rng.u32()) << 32)
}
// u32n returns a pseudorandom 32-bit unsigned `u32` in range `[0, max)`.
[inline]
pub fn (mut rng PCG32RNG) u32n(max u32) u32 {
if max == 0 {
eprintln('max must be positive')
exit(1)
}
// To avoid bias, we need to make the range of the RNG a multiple of
// max, which we do by dropping output less than a threshold.
threshold := (-max % max)
// Uniformity guarantees that loop below will terminate. In practice, it
// should usually terminate quickly; on average (assuming all max's are
// equally likely), 82.25% of the time, we can expect it to require just
// one iteration. In practice, max's are typically small and only a
// tiny amount of the range is eliminated.
for {
r := rng.u32()
if r >= threshold {
return (r % max)
}
}
return u32(0)
}
// u64n returns a pseudorandom 64-bit unsigned `u64` in range `[0, max)`.
[inline]
pub fn (mut rng PCG32RNG) u64n(max u64) u64 {
if max == 0 {
eprintln('max must be positive')
exit(1)
}
threshold := (-max % max)
for {
r := rng.u64()
if r >= threshold {
return (r % max)
}
}
return u64(0)
}
// u32_in_range returns a pseudorandom 32-bit unsigned `u32` in range `[min, max)`.
[inline]
pub fn (mut rng PCG32RNG) u32_in_range(min u32, max u32) u32 {
if max <= min {
eprintln('max must be greater than min')
exit(1)
}
return min + rng.u32n(u32(max - min))
}
// u64_in_range returns a pseudorandom 64-bit unsigned `u64` in range `[min, max)`.
[inline]
pub fn (mut rng PCG32RNG) u64_in_range(min u64, max u64) u64 {
if max <= min {
eprintln('max must be greater than min')
exit(1)
}
return min + rng.u64n(max - min)
}
// int returns a 32-bit signed (possibly negative) `int`.
[inline]
pub fn (mut rng PCG32RNG) int() int {
return int(rng.u32())
}
// i64 returns a 64-bit signed (possibly negative) `i64`.
[inline]
pub fn (mut rng PCG32RNG) i64() i64 {
return i64(rng.u64())
}
// int31 returns a 31-bit positive pseudorandom `int`.
[inline]
pub fn (mut rng PCG32RNG) int31() int {
return int(rng.u32() >> 1)
}
// int63 returns a 63-bit positive pseudorandom `i64`.
[inline]
pub fn (mut rng PCG32RNG) int63() i64 {
return i64(rng.u64() >> 1)
}
// intn returns a 32-bit positive `int` in range `[0, max)`.
[inline]
pub fn (mut rng PCG32RNG) intn(max int) int {
if max <= 0 {
eprintln('max has to be positive.')
exit(1)
}
return int(rng.u32n(u32(max)))
}
// i64n returns a 64-bit positive `i64` in range `[0, max)`.
[inline]
pub fn (mut rng PCG32RNG) i64n(max i64) i64 {
if max <= 0 {
eprintln('max has to be positive.')
exit(1)
}
return i64(rng.u64n(u64(max)))
}
// int_in_range returns a 32-bit positive `int` in range `[0, max)`.
[inline]
pub fn (mut rng PCG32RNG) int_in_range(min int, max int) int {
if max <= min {
eprintln('max must be greater than min.')
exit(1)
}
return min + rng.intn(max - min)
}
// i64_in_range returns a 64-bit positive `i64` in range `[0, max)`.
[inline]
pub fn (mut rng PCG32RNG) i64_in_range(min i64, max i64) i64 {
if max <= min {
eprintln('max must be greater than min.')
exit(1)
}
return min + rng.i64n(max - min)
}
// f32 returns a pseudorandom `f32` value in range `[0, 1)`.
[inline]
pub fn (mut rng PCG32RNG) f32() f32 {
return f32(rng.u32()) / constants.max_u32_as_f32
}
// f64 returns a pseudorandom `f64` value in range `[0, 1)`.
[inline]
pub fn (mut rng PCG32RNG) f64() f64 {
return f64(rng.u64()) / constants.max_u64_as_f64
}
// f32n returns a pseudorandom `f32` value in range `[0, max)`.
[inline]
pub fn (mut rng PCG32RNG) f32n(max f32) f32 {
if max <= 0 {
eprintln('max has to be positive.')
exit(1)
}
return rng.f32() * max
}
// f64n returns a pseudorandom `f64` value in range `[0, max)`.
[inline]
pub fn (mut rng PCG32RNG) f64n(max f64) f64 {
if max <= 0 {
eprintln('max has to be positive.')
exit(1)
}
return rng.f64() * max
}
// f32_in_range returns a pseudorandom `f32` in range `[min, max)`.
[inline]
pub fn (mut rng PCG32RNG) f32_in_range(min f32, max f32) f32 {
if max <= min {
eprintln('max must be greater than min')
exit(1)
}
return min + rng.f32n(max - min)
}
// i64_in_range returns a pseudorandom `i64` in range `[min, max)`.
[inline]
pub fn (mut rng PCG32RNG) f64_in_range(min f64, max f64) f64 {
if max <= min {
eprintln('max must be greater than min')
exit(1)
}
return min + rng.f64n(max - min)
}
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