Working with phasor re-rotation

ch32v/ch32v203-goertzel/ttest/floattestt.c

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+#include <stdio.h>
+#include <math.h>
+
+int main()
+{
+	const float omegaPerSample = 3.1415926*2.0 / 128; // pi / 200
+
+	// Only divide by 128 to show two cycles.
+
+	const int numSamples = 256; // enough to go from 0 to 2pi
+
+	float phase = 0;
+	//for( float phase = 0; phase < 3.1415926*2.0; phase += 0.01 )
+	{
+		float coeff = 2 * cos( omegaPerSample );
+		int i;
+
+		// TRICKY: When you want a sinewave, initialize with omegaPerSample.  This
+		// is crucial.  The initial state will have massive consequences.
+		float sprev = omegaPerSample;
+		float sprev2 = 0;
+		for( i = 0; i < numSamples; i++ )
+		{
+			// If you wanted to do a DFT, set SAMPLE to your incoming sample.
+			float SAMPLE = 65536 * sin( phase + i * omegaPerSample );
+
+			// Here is where the magic happens.
+			float s = SAMPLE + coeff * sprev - sprev2;
+			sprev2 = sprev;
+			sprev = s;
+
+		// For DFT, your power will be:
+		float power = sprev*sprev + sprev2*sprev2 - (coeff * sprev * sprev2);
+		//printf( "Power: %f\n", power );
+
+		float coeff_s = 2 * sin( omegaPerSample );
+		double rR = 0.5 * coeff   * sprev - sprev2;
+		double rI = 0.5 * coeff_s * sprev;
+		printf( "%d,%f,%f\n", i, rR, rI);
+
+		}
+
+	}
+}