- log2_ln.hpp/cpp: Plugin's exact ln(float) polynomial from 535a70
(0x1802a24c0). IEEE 754 bit extraction + Horner evaluation.
Coefficients extracted from binary at 0x181f81f80..0x181f821c0.
Max error ~3e-6 for typical inputs.
- spectral.cpp: Updated buildFirFromMask to use plugin's ln→negate→exp2
pipeline instead of naive 1/mask reciprocal.
- exp2_tables.hpp/cpp: Already contains plugin's exp2 tables (0x26b820).
Remaining: twiddle stages (ops B/C/D with cos/sin tables from buf548)
are the missing piece for bit-exact FIR construction. These are
FFT butterflies already implemented in fft.hpp but need integration
into the FIR pipeline.
