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98 lines
2.7 KiB
V
98 lines
2.7 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 pcg32
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import rand.seed
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pub const seed_len = 4
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// PCG32RNG ported from http://www.pcg-random.org/download.html,
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// https://github.com/imneme/pcg-c-basic/blob/master/pcg_basic.c, and
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// https://github.com/imneme/pcg-c-basic/blob/master/pcg_basic.h
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pub struct PCG32RNG {
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mut:
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state u64 = u64(0x853c49e6748fea9b) ^ seed.time_seed_64()
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inc u64 = u64(0xda3e39cb94b95bdb) ^ seed.time_seed_64()
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bytes_left int
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buffer u32
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}
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// seed seeds the PCG32RNG with 4 `u32` values.
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// The first 2 represent the 64-bit initial state as `[lower 32 bits, higher 32 bits]`
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// The last 2 represent the 64-bit stream/step of the PRNG.
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pub fn (mut rng PCG32RNG) seed(seed_data []u32) {
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if seed_data.len != 4 {
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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].')
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exit(1)
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}
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init_state := u64(seed_data[0]) | (u64(seed_data[1]) << 32)
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init_seq := u64(seed_data[2]) | (u64(seed_data[3]) << 32)
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rng.state = u64(0)
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rng.inc = (init_seq << u64(1)) | u64(1)
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rng.u32()
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rng.state += init_state
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rng.u32()
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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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fn (mut rng PCG32RNG) 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.u32()
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rng.bytes_left = 3
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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 16-bit unsigned integer (`u16`).
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[inline]
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pub fn (mut rng PCG32RNG) 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.u32()
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rng.buffer = ans >> 16
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rng.bytes_left = 2
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return u16(ans)
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}
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// u32 returns a pseudorandom unsigned `u32`.
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[inline]
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fn (mut rng PCG32RNG) u32() u32 {
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oldstate := rng.state
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rng.state = oldstate * (6364136223846793005) + rng.inc
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xorshifted := u32(((oldstate >> u64(18)) ^ oldstate) >> u64(27))
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rot := u32(oldstate >> u64(59))
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return (xorshifted >> rot) | (xorshifted << ((-rot) & u32(31)))
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}
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// u64 returns a pseudorandom 64-bit unsigned `u64`.
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[inline]
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pub fn (mut rng PCG32RNG) u64() u64 {
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return u64(rng.u32()) | (u64(rng.u32()) << 32)
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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 PCG32RNG) block_size() int {
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return 32
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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 PCG32RNG) free() {
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unsafe { free(rng) }
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}
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