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