max / audiofiles

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1	//! Reverse operation: reverse frame order while preserving channel layout.
2
3	/// Reverse sample data in-place, preserving channel order within each frame.
4	///
5	/// For stereo audio, this reverses the order of L/R frame pairs without
6	/// swapping L and R within a frame.
7	pub fn apply_reverse(samples: &mut [f32], channels: u16) {
8	let ch = channels as usize;
9	if ch == 0 \|\| samples.is_empty() {
10	return;
11	}
12
13	let num_frames = samples.len() / ch;
14	// Swap frames from outside in
15	for i in 0..num_frames / 2 {
16	let j = num_frames - 1 - i;
17	for c in 0..ch {
18	samples.swap(i * ch + c, j * ch + c);
19	}
20	}
21	}
22
23	#[cfg(test)]
24	mod tests {
25	use super::*;
26
27	#[test]
28	fn reverse_mono() {
29	let mut samples = vec![1.0, 2.0, 3.0, 4.0, 5.0];
30	apply_reverse(&mut samples, 1);
31	assert_eq!(samples, vec![5.0, 4.0, 3.0, 2.0, 1.0]);
32	}
33
34	#[test]
35	fn reverse_stereo() {
36	// 3 frames: [L0,R0, L1,R1, L2,R2]
37	let mut samples = vec![1.0, 2.0, 3.0, 4.0, 5.0, 6.0];
38	apply_reverse(&mut samples, 2);
39	// Reversed frames: [L2,R2, L1,R1, L0,R0]
40	assert_eq!(samples, vec![5.0, 6.0, 3.0, 4.0, 1.0, 2.0]);
41	}
42
43	#[test]
44	fn reverse_single_frame() {
45	let mut samples = vec![1.0, 2.0];
46	apply_reverse(&mut samples, 2);
47	assert_eq!(samples, vec![1.0, 2.0]);
48	}
49
50	#[test]
51	fn reverse_empty() {
52	let mut samples: Vec<f32> = vec![];
53	apply_reverse(&mut samples, 1);
54	assert!(samples.is_empty());
55	}
56
57	#[test]
58	fn reverse_double_is_identity() {
59	let original = vec![1.0, 2.0, 3.0, 4.0, 5.0, 6.0];
60	let mut samples = original.clone();
61	apply_reverse(&mut samples, 2);
62	apply_reverse(&mut samples, 2);
63	assert_eq!(samples, original);
64	}
65	}
66