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/// A Sample State
use crate::helper::*;
use xmrs::sample::Sample;
// Float math backend (only needed when `std` is disabled).
// Priority: std > libm > micromath.
#[cfg(all(not(feature = "std"), not(feature = "libm"), feature = "micromath"))]
#[allow(unused_imports)]
use micromath::F32Ext;
#[cfg(all(not(feature = "std"), feature = "libm"))]
#[allow(unused_imports)]
use num_traits::float::Float;
const M: u32 = 25; // 25 bits for fract part seems the better i can have
const M_MASK: u32 = (1 << M) - 1;
#[derive(Clone)]
pub struct StateSample<'a> {
sample: &'a Sample,
finetune: f32,
/// current sustain state
sustained: bool,
/// current seek position
position: (u32, u32), // ( Position, Fract part M shifted )
/// step is freq / rate
step: Option<u32>, // step, M shifted
// Output frequency
rate: f32,
}
impl<'a> StateSample<'a> {
pub fn new(sample: &'a Sample, rate: f32) -> Self {
let finetune = sample.finetune;
Self {
sample,
finetune,
sustained: true,
position: (0, 0),
step: None,
rate,
}
}
pub fn reset(&mut self) {
self.position = (0, 0);
self.sustained = true;
self.step = None;
}
pub fn set_step(&mut self, frequency: f32) {
if self.sample.is_empty() {
self.disable();
} else {
self.step = Some(((1 << M) as f32 * (frequency / self.rate)) as u32);
}
}
pub fn is_enabled(&self) -> bool {
self.step.is_some()
}
/// `true` if the underlying sample has any kind of loop (forward,
/// ping-pong, or sustain). Used by the voice pool's eviction
/// heuristic — looping voices can ring indefinitely so they're
/// cheaper to drop than one-shot tails.
pub fn is_looping(&self) -> bool {
use xmrs::sample::LoopType;
self.sample.loop_flag != LoopType::No || self.sample.sustain_loop_flag != LoopType::No
}
pub fn disable(&mut self) {
self.step = None;
}
pub fn get_panning(&self) -> f32 {
self.sample.panning
}
pub fn get_volume(&self) -> f32 {
self.sample.volume
}
/// use sample finetune or force if finetune arg!=0
pub fn get_finetuned_pitch(&self) -> f32 {
self.sample.relative_pitch as f32 + self.finetune
}
pub fn set_finetune(&mut self, finetune: f32) {
self.finetune = finetune;
}
pub fn set_sustained(&mut self, sustained: bool) {
self.position.0 = self
.sample
.meta_seek(self.position.0 as usize, self.sustained) as u32;
self.sustained = sustained;
}
fn tick(&mut self) -> (f32, f32) {
// Ask the sample where we actually are. `seek` returns `None`
// when the play head has run past the end of a non-looping
// sample — at which point the voice is done and must be shut
// off, otherwise it would hold the tail frame indefinitely and
// produce an audible drone on any instrument whose tail isn't
// silent.
let pos = self.position.0 as usize;
let useek = match self.sample.seek(pos, self.sustained) {
Some(s) => s,
None => {
self.disable();
return (0.0, 0.0);
}
};
// Linear interpolation peek: the "next" sample follows the same
// rules. If the next frame is past the end, reuse the current
// one rather than blending into silence.
let vseek = self.sample.seek(pos + 1, self.sustained).unwrap_or(useek);
let t = self.get_position_fraction() as f32 / (1 << M) as f32;
let u = self.sample.at(useek);
let v = self.sample.at(vseek);
self.increment_position();
(lerp(u.0, v.0, t), lerp(u.1, v.1, t))
}
pub fn set_position(&mut self, position: usize) {
self.position.0 = position as u32;
self.position.1 = 0;
}
/// Length of the underlying sample in sample frames. Used by the
/// channel's Oxx-past-end branch to decide whether to clamp
/// (IT old-effects) or drop the offset (IT default / XM / etc.).
pub fn sample_len(&self) -> usize {
self.sample.len()
}
#[inline(always)]
fn increment_position(&mut self) -> u32 {
if let Some(step) = self.step {
// Split `step` into integer and fractional parts *before*
// accumulating, so the fractional register never overflows
// u32 on 32-bit targets. With M = 25:
// step & M_MASK < 2^25
// position.1 <= M_MASK < 2^25
// → position.1 + (step & M_MASK) < 2^26 (safe u32 add)
//
// The naive `position.1 += step` panicked whenever `step`
// saturated to u32::MAX — which happens as soon as the
// `f32 as u32` cast in `set_step` is fed a multi-MHz
// frequency (e.g. S3M portamento-up driving the Amiga
// period toward zero). Branchless form below keeps the
// hot path free of conditional jumps.
self.position.1 += step & M_MASK;
let carry = self.position.1 >> M; // 0 or 1
self.position.0 = self
.position
.0
.wrapping_add((step >> M).wrapping_add(carry));
self.position.1 &= M_MASK;
}
self.position.0
}
#[inline(always)]
fn get_position_fraction(&self) -> u32 {
self.position.1 & M_MASK
}
}
impl<'a> Iterator for StateSample<'a> {
type Item = (f32, f32);
fn next(&mut self) -> Option<Self::Item> {
if self.is_enabled() {
Some(self.tick())
} else {
None
}
}
}