;
; iron_spectrum.hsp — 音声スペクトラム解析 (簡易 DFT)
; Pure HSP。可視化用途向け。
;
#ifndef __iron_spectrum_hsp__
#define __iron_spectrum_hsp__
#module iron_spectrum

#define PI2_S 6.28318530718

; Compute magnitude spectrum of audio samples
; samples: int array (16-bit PCM), n: sample count, bins: output double array
#deffunc spectrum_compute array samples, int n, array bins, int num_bins, \
	local re, local im, local k, local i, local angle
	dimtype bins, 3, num_bins
	repeat num_bins
		k = cnt
		re = 0.0 : im = 0.0
		repeat n
			i = cnt
			angle = PI2_S * double(k) * double(i) / double(n)
			re += double(samples(i)) * cos(angle)
			im -= double(samples(i)) * sin(angle)
		loop
		bins(k) = sqrt(re * re + im * im) / double(n)
	loop
	return

#global
#endif