89 lines
2.3 KiB
Rust
89 lines
2.3 KiB
Rust
use std::num::Wrapping;
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#[derive(Debug)]
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pub struct MT19937 {
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mt: Vec<u32>,
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index: usize,
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}
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const N: usize = 624;
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impl MT19937 {
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pub fn new() -> MT19937 {
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let mut mt = MT19937 {
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mt: vec![0; N],
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index: N + 1,
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};
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mt.seed(5489);
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mt
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}
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pub fn splice(&mut self, state: Vec<u32>) {
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self.mt = state;
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self.index = 624;
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}
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pub fn seed(&mut self, seed: u32) {
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const F: u32 = 1_812_433_253;
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self.mt[0] = seed;
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for i in 1..N {
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self.mt[i] = (Wrapping(F) * Wrapping(self.mt[i - 1] ^ (self.mt[i - 1] >> 30))
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+ Wrapping(i as u32))
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.0;
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}
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self.twist();
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}
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pub fn extract_bytes(&mut self) -> [u8; 4] {
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let n = self.extract_number();
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n.to_ne_bytes()
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}
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pub fn extract_number(&mut self) -> u32 {
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match self.index.cmp(&N) {
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std::cmp::Ordering::Equal => self.twist(),
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std::cmp::Ordering::Greater => panic!("Generator was never seeded"),
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std::cmp::Ordering::Less => (),
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}
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const S: u32 = 7;
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const T: u32 = 15;
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const U: u32 = 11;
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const B: u32 = 0x9D2C_5680;
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const C: u32 = 0xEFC6_0000;
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const D: u32 = 0xFFFF_FFFF;
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const L: u32 = 18;
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let mut y = self.mt[self.index];
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y = y ^ ((y >> U) & D);
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y = y ^ ((y << S) & B);
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y = y ^ ((y << T) & C);
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y = y ^ (y >> L);
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self.index += 1;
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y
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}
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fn twist(&mut self) {
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const M: usize = 397;
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const A: u32 = 0x9908_B0DF;
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const LOWER_MASK: u32 = 0x7fff_ffff;
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const UPPER_MASK: u32 = 0x8000_0000;
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const FIRST_HALF: usize = N - M;
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for i in 0..FIRST_HALF {
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let bits = self.mt[i] & UPPER_MASK | self.mt[i + 1] & LOWER_MASK;
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self.mt[i] = self.mt[i + M] ^ (bits >> 1) ^ ((bits & 1) * A);
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}
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for i in FIRST_HALF..(N - 1) {
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let bits = self.mt[i] & UPPER_MASK | self.mt[i + 1] & LOWER_MASK;
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self.mt[i] = self.mt[i - FIRST_HALF] ^ (bits >> 1) ^ ((bits & 1) * A);
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}
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let i = N - 1;
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let bits = self.mt[i] & UPPER_MASK | self.mt[0] & LOWER_MASK;
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self.mt[i] = self.mt[M - 1] ^ (bits >> 1) ^ ((bits & 1) * A);
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self.index = 0;
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}
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}
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