pounder_test/dsp/src/unwrap.rs

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use serde::{Deserialize, Serialize};
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/// Subtract `y - x` with signed overflow.
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///
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/// This is very similar to `i32::overflowing_sub(y, x)` except that the
/// overflow indicator is not a boolean but the signum of the overflow.
/// Additionally it's typically faster.
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///
/// Returns:
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/// A tuple containg the (wrapped) difference `y - x` and the signum of the
/// overflow.
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#[inline(always)]
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pub fn overflowing_sub(y: i32, x: i32) -> (i32, i8) {
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let delta = y.wrapping_sub(x);
let wrap = (delta >= 0) as i8 - (y >= x) as i8;
(delta, wrap)
}
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/// Overflow unwrapper.
///
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/// This is unwrapping as in the phase and overflow unwrapping context, not
/// unwrapping as in the `Result`/`Option` context.
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#[derive(Copy, Clone, Default, Deserialize, Serialize)]
pub struct Unwrapper {
// last input
x: i32,
// last wraps
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w: i32,
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}
impl Unwrapper {
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/// Unwrap a new sample from a sequence and update the unwrapper state.
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///
/// Args:
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/// * `x`: New sample
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///
/// Returns:
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/// A tuple containing the (wrapped) difference `x - x_old` and the
/// signed number of wraps accumulated by the new sample.
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pub fn update(&mut self, x: i32) -> (i32, i32) {
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let (dx, dw) = overflowing_sub(x, self.x);
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self.x = x;
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self.w = self.w.wrapping_add(dw as i32);
(dx, self.w)
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}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn mini() {
for (x0, x1, v) in [
(0i32, 0i32, 0i8),
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(0, 1, 0),
(0, -1, 0),
(1, 0, 0),
(-1, 0, 0),
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(0, 0x7fff_ffff, 0),
(-1, 0x7fff_ffff, -1),
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(-2, 0x7fff_ffff, -1),
(-1, -0x8000_0000, 0),
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(0, -0x8000_0000, 0),
(1, -0x8000_0000, 1),
(-0x6000_0000, 0x6000_0000, -1),
(0x6000_0000, -0x6000_0000, 1),
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(-0x4000_0000, 0x3fff_ffff, 0),
(-0x4000_0000, 0x4000_0000, -1),
(-0x4000_0000, 0x4000_0001, -1),
(0x4000_0000, -0x3fff_ffff, 0),
(0x4000_0000, -0x4000_0000, 0),
(0x4000_0000, -0x4000_0001, 1),
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]
.iter()
{
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let (dx, w) = overflowing_sub(*x1, *x0);
assert_eq!(*v, w, " = overflowing_sub({:#x}, {:#x})", *x0, *x1);
let (dx0, w0) = x1.overflowing_sub(*x0);
assert_eq!(w0, w != 0);
assert_eq!(dx, dx0);
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}
}
}