feat(dsp): structural FUN_180529fe0 chain components + fn529fe0_check (step 1, module 1)

dsp/fn529fe0.hpp

@@ -0,0 +1,41 @@
+#pragma once
+#include <cstddef>
+#include <vector>
+
+// Structural transcription of the soothe2 mask-apply mono path
+// FUN_180529fe0 (0x5408b8==0), BITEXACT_PLAN step 1. Uses the live-captured
+// tables (dsp/rt_mask_tables.*, dsp/rt_weights.*) and the exact step sequence
+// from NOTES_LEVEL:820-840 / :237-253.
+//
+// Unlike the empirical bridge (dsp/framed_model.cpp), this reproduces the real
+// reduction/exp2-domain chain:
+//   scale -> IIR1 -> copy -> IIR2 -> mirror -> blend(0.8 pedestal)
+//   -> exp2(-level)*blend -> combine/acc -> warp(kBand768*kWarp)
+//   -> IIR3 x2 -> dry/wet -> (FFT-conv is step 4, separate module)
+//
+// The IIR/weight tables are indexed 0..N/2 of the INTERNAL grid (N=4096/SR=48000);
+// per-bin level is supplied by the caller (level-path), same xv domain as bridge
+// (level = am/res) but fed through the structural chain instead of the LUT bridge.
+namespace fn529fe0 {
+
+// All per-bin buffers are length nbin = nfft/2+1 (internal grid).
+// IIR stage: y[i] = A[i]*acc + B[i]*x[i]; acc=y (first-order leaky, like leveltrack).
+void iir1(float* x, const double* A, const double* B, size_t nbin, double acc0);
+
+// Blend step 6: f6f8[k] = freqaxis[k]*(1-mix) + mix*0.8;  out = exp2(-x)*f6f8.
+void blend_exp2(float* mask, const float* x, const float* freqaxis,
+                float mix, size_t nbin);
+
+// Combine step 7 (reduction/exp2 domain): accumulates per-band.
+//   acc = band - f6f8;  += wAtt[mirror]*upper;  += wRel[mirror]*lower;  += band
+// In-place on acc; band and f6f8 are inputs (len nbin, mirrored to full nfft).
+void combine_acc(double* acc, const float* band, const float* f6f8,
+                 const float* wAtt, const float* wRel, size_t nfft);
+
+// Warp step 8: mask *= kBand768 * kWarp (two multiplies).
+void warp_mask(float* mask, const float* kBand768, const float* kWarp, size_t nbin);
+
+// Dry/wet step 10 (fVar30=1, 0x540888=1 -> identity for default).
+void dry_wet(float* mask, float fVar30, float wet, size_t nbin);
+
+}  // namespace fn529fe0