P3.4: transcribe plugin's own vectorized ln(x) (vlog.cpp, minimax ln(1+x) poly + ln2 range-reduction); correct prior misread — dispatch reaches runtime ln, not FFT; vlog_check ALL OK (rel 2.4e-7)

dsp/vlog.hpp

@@ -0,0 +1,20 @@
+#pragma once
+#include <cstdint>
+
+namespace vlog {
+
+// Scalar transcription of the vectorized natural-logarithm kernel at 0x1802a24c0
+// (soothe2 VST3, MSVC x86-64 AVX2, extracted from /tmp/snap_rt.bin).
+//
+// The kernel computes  dst[i] = ln(src[i])  elementwise in single precision,
+// using its own minimax polynomial + ln(2) range reduction driven by float
+// bit-manipulation (the "2/3" magic exponent/mantissa split). A scalar
+// double-precision Cody-Waite ln handles the slow path for special values.
+//
+// NOTE: despite the file name, this kernel is a natural logarithm, NOT an FFT
+// butterfly. It sits in the spectral (log-magnitude) processing path, not the
+// complex FFT transform. The signature below mirrors the actual code: float,
+// out-of-place, real (src != dst is allowed).
+void log_f32(const float* src, float* dst, uint32_t n);
+
+} // namespace vlog