mirror of https://github.com/fralalonde/dipstick
50 lines
1.7 KiB
Rust
50 lines
1.7 KiB
Rust
//! PCG32 random number generation for fast sampling
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//! Kept here for low dependency count.
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#![cfg_attr(feature = "tool_lints", allow(clippy::unreadable_literal))]
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#![allow(clippy::unreadable_literal)]
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use std::cell::RefCell;
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fn seed() -> u64 {
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let seed = 5573589319906701683_u64;
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let seed = seed
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.wrapping_mul(6364136223846793005)
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.wrapping_add(1442695040888963407)
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.wrapping_add(time::precise_time_ns());
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seed.wrapping_mul(6364136223846793005)
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.wrapping_add(1442695040888963407)
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}
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/// quickly return a random int
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fn pcg32_random() -> u32 {
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thread_local! {
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static PCG32_STATE: RefCell<u64> = RefCell::new(seed());
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}
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PCG32_STATE.with(|state| {
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let old_state: u64 = *state.borrow();
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// XXX could generate the increment from the thread ID
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*state.borrow_mut() = old_state
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.wrapping_mul(6364136223846793005)
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.wrapping_add(1442695040888963407);
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((((old_state >> 18) ^ old_state) >> 27) as u32).rotate_right((old_state >> 59) as u32)
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})
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}
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/// Convert a floating point sampling rate to an integer so that a fast integer RNG can be used
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/// Float rate range is between 1.0 (send 100% of the samples) and 0.0 (_no_ samples taken)
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/// . | float rate | int rate | percentage
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/// ---- | ---------- | -------- | ----
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/// all | 1.0 | 0x0 | 100%
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/// none | 0.0 | 0xFFFFFFFF | 0%
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pub fn to_int_rate(float_rate: f64) -> u32 {
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assert!((0.0..=1.0).contains(&float_rate));
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((1.0 - float_rate) * f64::from(::std::u32::MAX)) as u32
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}
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/// randomly select samples based on an int rate
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pub fn accept_sample(int_rate: u32) -> bool {
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pcg32_random() > int_rate
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}
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