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# Reverb, using FFTW if available and BQN-based FFT if not
Reverb ← {
lw‿lx ← (¯1⊑≢)¨ 𝕨‿𝕩
! 0<lw
# Use the overlap-add method.
o ← lw-1 # Overlap length
k ← lx+o # Result length
n ← k⌊(2⋆14)⌈3×o # Window length, including overlap
n ⌈⌾(2⋆⁼⊢)↩ # Round up to power of two
l ← n-o # Without overlap
k0← ⌈⌾(÷⟜l) k # Rounded up
𝕨 {
CW ← (n↑𝕨) _rev1
{t←0 ⋄ k↑⥊ {r‿s←(-o)(t⊸+⌾(o⊸↑)∘↓⋈↑)CW𝕩⋄t↩s⋄r}˘ ∘‿l⥊k0↑𝕩}⎉1 𝕩
}⎉(1≍1+0⌈-˜○=) 𝕩
}
# Convolve 𝕗 and 𝕗≠⊸↑𝕩, assuming length of 𝕗 is a power of 2
rev1 ← {𝕊
# Use the half-complex form of FFTW
# Converts e.g. 8 reals to r0,r1,r2,r3,r4,i3,i2,i1 and back
pl ← ">" ∾ plan ← "*:i32"
Fn ← "/usr/lib/libfftw3.so.3"⊸(•BQN"•FFI")
createPlan ← Fn plan‿"fftw_plan_r2r_1d"‿"i32"‿"*f64"‿"&f64"‿"i32"‿"i32"
destroyPlan ← Fn ""‿"fftw_destroy_plan"‿pl
executePlan ← Fn ""‿"fftw_execute"‿pl
FFTR ← { 𝕊⁼𝕩: 1𝕊𝕩 ;
plan‿out ← CreatePlan ⟨≠𝕩,𝕩,0¨𝕩,𝕨⊣0,2⋆6⟩
ExecutePlan plan
DestroyPlan plan
out
}
{
mh←-nh←1-˜2÷˜n←≠𝕗
M ← (mh(↓-0∾0∾˜⌽∘↑)×) ∾ nh(⌽∘↑+-⊸↑)×⟜⌽○(1⊸↓) # Scrambled complex ×
(n ÷˜ FFTR 𝕗)⊸M⌾FFTR n⊸↑
}
}⎊{𝕊
fft ← •Import "fft.bqn"
M ← -˝∘× ≍ +˝∘×⟜⌽ # Complex multiplication
{⊏ · (FFT 𝕗)⊸M⌾FFT (≠𝕗)⊸↑}
}@
Reverb
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