pounder_test/dsp/src/unwrap.rs

use serde::{Deserialize, Serialize};

/// Subtract `y - x` with signed overflow.
///
/// 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.
///
/// Returns:
/// A tuple containg the (wrapped) difference `y - x` and the signum of the
/// overflow.
#[inline(always)]
pub fn overflowing_sub(y: i32, x: i32) -> (i32, i8) {
    let delta = y.wrapping_sub(x);
    let wrap = (delta >= 0) as i8 - (y >= x) as i8;
    (delta, wrap)
}

/// Overflow unwrapper.
///
/// This is unwrapping as in the phase and overflow unwrapping context, not
/// unwrapping as in the `Result`/`Option` context.
#[derive(Copy, Clone, Default, Deserialize, Serialize)]
pub struct Unwrapper {
    // last input
    x: i32,
    // last wraps
    w: i32,
}

impl Unwrapper {
    /// Unwrap a new sample from a sequence and update the unwrapper state.
    ///
    /// Args:
    /// * `x`: New sample
    ///
    /// Returns:
    /// A tuple containing the (wrapped) difference `x - x_old` and the
    /// signed number of wraps accumulated by the new sample.
    pub fn update(&mut self, x: i32) -> (i32, i32) {
        let (dx, dw) = overflowing_sub(x, self.x);
        self.x = x;
        self.w = self.w.wrapping_add(dw as i32);
        (dx, self.w)
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn mini() {
        for (x0, x1, v) in [
            (0i32, 0i32, 0i8),
            (0, 1, 0),
            (0, -1, 0),
            (1, 0, 0),
            (-1, 0, 0),
            (0, 0x7fff_ffff, 0),
            (-1, 0x7fff_ffff, -1),
            (-2, 0x7fff_ffff, -1),
            (-1, -0x8000_0000, 0),
            (0, -0x8000_0000, 0),
            (1, -0x8000_0000, 1),
            (-0x6000_0000, 0x6000_0000, -1),
            (0x6000_0000, -0x6000_0000, 1),
            (-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),
        ]
        .iter()
        {
            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);
        }
    }
}