From 068d08bf44aafc1b36fec7302130f1a5b2fde08c Mon Sep 17 00:00:00 2001
From: ZoRo <dos21h@gmail.com>
Date: Fri, 9 Jul 2021 09:01:22 +0100
Subject: FIR filter C snippet

---
 fir1/simple_fir.c | 97 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 97 insertions(+)
 create mode 100644 fir1/simple_fir.c

(limited to 'fir1/simple_fir.c')

diff --git a/fir1/simple_fir.c b/fir1/simple_fir.c
new file mode 100644
index 0000000..8f48569
--- /dev/null
+++ b/fir1/simple_fir.c
@@ -0,0 +1,97 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <math.h>
+
+double sinc(double x) {
+    if (x>-1.0E-5 && x < 1.0E-5) return (1.0);
+    return sin(x)/x;
+}
+
+int main() {
+
+	const int buf_N=200;
+	//int N1 = N/2;
+    
+    int i=0;
+    double h[buf_N],w[buf_N];
+    int filter_N=20;
+    int even = filter_N ? 0: 1;
+    int filter_N1=filter_N/2;
+    int filter_FS_hz=10000;
+    int filter_FC_hz=2000;
+    double omega_c=1.0*filter_FC_hz/filter_FS_hz;
+    double arg;
+    double dN;
+
+    //nullify all coefficients
+    for (i=0;i<filter_N;i++) {
+        h[i] = 0.0;
+        w[i] = 0.0;
+    }
+
+    //sinc the
+    for (i=0;i<filter_N;i++) {
+        arg = (double)i-(double)(filter_N-1)/2.0;
+        h[i] = omega_c * sinc(omega_c*arg*M_PI);
+    }
+
+
+    if (even) filter_N1+=1;
+
+    #if 1
+    //rectangular window
+    
+    for (i=0;i<filter_N1;i++) {
+        w[i] = 1.0;
+    }
+    #endif
+
+    #if 0
+    //hamming window
+    for (i=0;i<filter_N1;i++) {
+        arg = (double)i-(double)(filter_N-1)/2.0;
+        w[i] = 0.54+0.46*cos(2*M_PI*arg/filter_N);
+
+    }
+    #endif
+
+    #if 0
+    //hanning window
+    for (i=0;i<filter_N1;i++) {
+        arg = (double)i-(double)(filter_N-1)/2.0;
+        w[i] = 0.5+(1-0.5)*cos(2*M_PI*arg/filter_N);
+
+    }
+    #endif
+
+    #if 0
+    //blackman window
+    for (i=0;i<filter_N1;i++) {
+        arg = (double)i-(double)(filter_N-1)/2.0;
+        w[i] = 0.42
+        +0.50*cos(2*M_PI*arg/(filter_N-1))
+        +0.08*cos(4*M_PI*arg/(filter_N-1));
+
+    }
+    #endif
+
+    //flip window
+    for (i=0;i<filter_N1;i++) {
+        w[filter_N-i-1] = w[i];
+    }
+
+    //convolution
+    for (i=0;i<filter_N;i++) {
+        h[i] = h[i]*w[i];
+    }
+
+    
+    //print coefficients
+    printf("h=[\n");
+    for (i=0;i<filter_N;i++) {
+        printf("%f\n",h[i]);
+    }
+    printf("];\n");
+
+}
-- 
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