From 12ae71759075a98deed5728d972c50e7131c726f Mon Sep 17 00:00:00 2001
From: ozpv <39195175+ozpv@users.noreply.github.com>
Date: Sat, 16 May 2026 16:39:26 -0500
Subject: real time processing

---
 src/retain.rs | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)
 create mode 100644 src/retain.rs

(limited to 'src/retain.rs')

diff --git a/src/retain.rs b/src/retain.rs
new file mode 100644
index 0000000..bc3934a
--- /dev/null
+++ b/src/retain.rs
@@ -0,0 +1,30 @@
+use hashbrown::HashSet;
+use num_complex::Complex;
+
+#[inline(always)]
+pub fn retain_top_n_magnitudes(fft_real_signal: &mut [Complex<f32>], n: usize) {
+    // you'd be keeping the entire signal
+    if n >= fft_real_signal.len() {
+        return;
+    }
+
+    let mut indexed = fft_real_signal
+        .iter()
+        .copied()
+        .enumerate()
+        .collect::<Vec<(usize, Complex<f32>)>>();
+
+    let target = fft_real_signal.len() - n;
+    indexed.select_nth_unstable_by(target, |(_, c0), (_, c1)| c0.norm().total_cmp(&c1.norm()));
+
+    let top_indices = indexed[target..]
+        .iter()
+        .map(|&(i, _)| i)
+        .collect::<HashSet<usize>>();
+
+    for (i, val) in fft_real_signal.iter_mut().enumerate() {
+        if !top_indices.contains(&i) {
+            *val = Complex::ZERO;
+        }
+    }
+}
-- 
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