Сравнение постов

import std.stdio;

extern(C) __gshared string[] rt_options =

    [ "gcopt=minPoolSize:2K maxPoolSize:1M incPoolSize:4K" ];

auto fastAbs(float x) @system

{

	uint p = *(cast(uint*) &x);

	p &=0x7fffffff;

	return *(cast(float*) &p);

}

auto renormalize(Range)(Range r)

{

	import std.algorithm;

	auto maximalAbsoluteValue = r

								.map!(a => fastAbs(a))

								.fold!max;

	return r

			.map!(a => a / maximalAbsoluteValue);

}

void main()

{

	import std.algorithm;

	import std.complex;

	import std.math;

	import std.numeric;

	import std.random;

	import std.range;

	import ppmformats;

	auto rng = Random(unpredictableSeed);

	auto signalWithNoise(float x)

	{

		return (3.3 * sin(2*x)) + uniform(-0.3, 0.3, rng);

	}

	alias squareWave = delegate(float x) {

	  return

          ((4 * 10) / (PI)) * (sin(x) + (sin(3 * x) / (3 * x)) + (sin(5 * x) /(5 * x)) + (sin(7 * x) / (7 * x)) + (sin(9 * x) / (9 * x)) + (sin(11 * x) / (11 * x))) + (sin(13 * x) / (13 * x)) + (sin(15 * x) / (15 * x)) + (sin(17 * x) / (17 * x));

	};

	auto signal = iota(0, 2_048)

						.map!squareWave;

	auto normalizedFFT(Range)(Range r)

	{

		return 

				r

				  .fft

				  .map!(a => 20.0f * log10(abs(a ^^ 2)))

				  .renormalize;

	}

	auto pd = signal

					.slide(1_024)

					.map!(a => normalizedFFT(a));

	auto img = new P6Image(1024, 1024);

	foreach (i, e; pd.enumerate)

	{

		foreach (j, s; e.enumerate)

		{

			img[i, j] = new RGBColor(

				cast(int) (0.8 * 255.0 * abs(s)),

				0,

				255 - cast(int) (255 * abs(s))

			);

		}

	}

	img.save(`fft.ppm`);		

}