From 495c887085a00aa6e3c10ce3f2ba614efba93ead Mon Sep 17 00:00:00 2001
From: Dan <null>
Date: Sat, 18 Apr 2020 18:27:18 +0100
Subject: [PATCH] Initial commit

---
 fftpipe.c | 92 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 makefile  | 18 +++++++++++
 2 files changed, 110 insertions(+)
 create mode 100644 fftpipe.c
 create mode 100644 makefile

diff --git a/fftpipe.c b/fftpipe.c
new file mode 100644
index 0000000..53ee911
--- /dev/null
+++ b/fftpipe.c
@@ -0,0 +1,92 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <getopt.h>
+#include <err.h>
+#include <math.h>
+#include <fftw3.h>
+
+int
+usage(const char* progname)
+{
+	fprintf(stderr, "usage: %s [-n count] [-m] [-w]\n", progname);
+	return 1;
+}
+
+void
+apply_window(float* samples, size_t n)
+{
+	for (size_t i = 0; i < n; ++i) {
+		float a = (1.0 - cosf((2.0f * M_PI * i) / n)) / 2.0;
+		samples[i] *= a;
+	}
+}
+
+int
+main(int argc, char** argv)
+{
+	int optch;
+	int nflag = 0;
+	const char* narg = NULL;
+	int mflag = 0;
+	int wflag = 0;
+
+	while ((optch = getopt(argc, argv, "n:mwh")) != -1) {
+		switch (optch) {
+		case 'n':
+			nflag = 1;
+			narg = optarg;
+			break;
+		case 'm':
+			mflag = 1;
+			break;
+		case 'w':
+			wflag = 1;
+			break;
+		case 'h':
+		default:
+			return usage(*argv);
+		}
+	}
+
+	if (!nflag)
+		return usage(*argv);
+
+	unsigned nsamples = strtoull(narg, NULL, 10);
+	float* samples = aligned_alloc(0x40, nsamples * sizeof(float));
+
+	if (samples == NULL)
+		err(1, "malloc()");
+
+	fftwf_complex* output = fftwf_malloc(nsamples * sizeof(fftwf_complex)); 
+	fftwf_plan plan = fftwf_plan_dft_r2c_1d(nsamples, samples, output, 0);
+
+	while (fread(samples, sizeof(float), nsamples, stdin) == nsamples) {
+		if (wflag) {
+			apply_window(samples, nsamples);
+		}
+
+		fftwf_execute(plan);
+
+		if (!mflag) {
+			fwrite(output, sizeof(fftwf_complex), nsamples / 2, stdout);
+		} else {
+			size_t i;
+			
+			for (i = 0; i < nsamples / 2; ++i) {
+				float mag = sqrtf(
+					output[i][0] * output[i][0] +
+					output[i][1] * output[i][1]
+				);
+
+				output[i / 2][i & 1] = mag;
+			}
+
+			memset(&output[i], 0, (nsamples - i) * sizeof(fftwf_complex));
+			fwrite(output, sizeof(float), nsamples / 2, stdout);
+		}
+	}
+
+	return 0;
+}
+
diff --git a/makefile b/makefile
new file mode 100644
index 0000000..d48e16a
--- /dev/null
+++ b/makefile
@@ -0,0 +1,18 @@
+.POSIX:
+.PHONY: install clean
+
+PREFIX=/usr/local
+
+CC=cc
+CFLAGS=-Wall -Wextra -Wshadow -Wpedantic -std=c99 -O2 -D_XOPEN_SOURCE
+LDFLAGS=$(shell pkg-config --libs --cflags --static fftw3 fftw3f) -static
+
+fftpipe: fftpipe.c
+	$(CC) $? $(LDFLAGS) $(CFLAGS) -o $@
+
+clean:
+	rm fftpipe
+
+install: fftpipe
+	cp $? $(PREFIX)/bin/
+