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[perf](trx-backend-soapysdr): use ring history for wfm resampler

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Signed-off-by: Stan Grams <sjg@haxx.space>
This commit is contained in:
Stan Grams
2026-03-01 01:34:50 +01:00
parent a6c3a85c8d
commit e7997f8492
1 changed files with 16 additions and 13 deletions
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src/trx-server/trx-backend/trx-backend-soapysdr/src/demod.rs
+16 -13
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@@ -80,21 +80,19 @@ fn build_wfm_resample_bank() -> [[f32; WFM_RESAMP_TAPS]; WFM_RESAMP_PHASES] {
bank
}
#[inline]
fn shift_append<const N: usize>(hist: &mut [f32; N], sample: f32) {
hist.rotate_left(1);
hist[N - 1] = sample;
}
#[inline]
fn polyphase_resample(
hist: &[f32; WFM_RESAMP_TAPS],
hist_head: usize,
bank: &[[f32; WFM_RESAMP_TAPS]; WFM_RESAMP_PHASES],
frac: f32,
) -> f32 {
let phase = (frac.clamp(0.0, 0.999_999) * WFM_RESAMP_PHASES as f32).round() as usize;
let phase = phase.min(WFM_RESAMP_PHASES - 1);
dot_product(&hist[..], &bank[phase][..])
let coeffs = &bank[phase];
let first = WFM_RESAMP_TAPS - hist_head.min(WFM_RESAMP_TAPS);
dot_product(&hist[hist_head..], &coeffs[..first])
+ dot_product(&hist[..hist_head], &coeffs[first..])
}
#[inline]
@@ -694,6 +692,8 @@ pub struct WfmStereoDecoder {
diff_hist: [f32; WFM_RESAMP_TAPS],
/// History ring for polyphase FIR resampling of the quadrature diff channel.
diff_q_hist: [f32; WFM_RESAMP_TAPS],
/// Shared ring head for the polyphase FIR histories; points to the oldest slot.
hist_head: usize,
/// Previous pilot blend sample for simple linear interpolation.
prev_blend: f32,
/// Fractional phase increment per composite sample = audio_rate / composite_rate.
@@ -753,6 +753,7 @@ impl WfmStereoDecoder {
sum_hist: [0.0; WFM_RESAMP_TAPS],
diff_hist: [0.0; WFM_RESAMP_TAPS],
diff_q_hist: [0.0; WFM_RESAMP_TAPS],
hist_head: 0,
prev_blend: 0.0,
output_phase_inc,
output_phase: 0.0,
@@ -845,9 +846,10 @@ impl WfmStereoDecoder {
// --- Polyphase FIR fractional resampling ---
// This uses a short windowed-sinc bank instead of cubic interpolation
// to reduce top-end overshoot/ringing near the audio cutoff.
shift_append(&mut self.sum_hist, sum);
shift_append(&mut self.diff_hist, diff_i);
shift_append(&mut self.diff_q_hist, diff_q);
self.sum_hist[self.hist_head] = sum;
self.diff_hist[self.hist_head] = diff_i;
self.diff_q_hist[self.hist_head] = diff_q;
self.hist_head = (self.hist_head + 1) % WFM_RESAMP_TAPS;
let prev_phase = self.output_phase;
self.output_phase += self.output_phase_inc;
@@ -861,9 +863,9 @@ impl WfmStereoDecoder {
// interval. The FIR bank reconstructs a band-limited sample using
// a fixed two-sample lookahead in the decoder.
let frac = ((1.0 - prev_phase) / self.output_phase_inc) as f32;
let sum_i = polyphase_resample(&self.sum_hist, &self.resample_bank, frac);
let diff_i = polyphase_resample(&self.diff_hist, &self.resample_bank, frac);
let diff_q = polyphase_resample(&self.diff_q_hist, &self.resample_bank, frac);
let sum_i = polyphase_resample(&self.sum_hist, self.hist_head, &self.resample_bank, frac);
let diff_i = polyphase_resample(&self.diff_hist, self.hist_head, &self.resample_bank, frac);
let diff_q = polyphase_resample(&self.diff_q_hist, self.hist_head, &self.resample_bank, frac);
let blend_i =
(self.prev_blend + frac * (stereo_blend_target - self.prev_blend)).clamp(0.0, 1.0);
self.prev_blend = stereo_blend_target;
@@ -953,6 +955,7 @@ impl WfmStereoDecoder {
self.sum_hist = [0.0; WFM_RESAMP_TAPS];
self.diff_hist = [0.0; WFM_RESAMP_TAPS];
self.diff_q_hist = [0.0; WFM_RESAMP_TAPS];
self.hist_head = 0;
self.prev_blend = 0.0;
self.output_phase = 0.0;
}