44 lines
1016 B
C
44 lines
1016 B
C
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#include <math.h>
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#include <stdlib.h>
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#include "fec.h"
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#define MAX_RANDOM 0x7fffffff
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/* Generate gaussian random double with specified mean and std_dev */
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double normal_rand(double mean, double std_dev)
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{
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double fac,rsq,v1,v2;
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static double gset;
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static int iset;
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if(iset){
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/* Already got one */
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iset = 0;
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return mean + std_dev*gset;
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}
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/* Generate two evenly distributed numbers between -1 and +1
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* that are inside the unit circle
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*/
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do {
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v1 = 2.0 * (double)random() / MAX_RANDOM - 1;
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v2 = 2.0 * (double)random() / MAX_RANDOM - 1;
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rsq = v1*v1 + v2*v2;
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} while(rsq >= 1.0 || rsq == 0.0);
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fac = sqrt(-2.0*log(rsq)/rsq);
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gset = v1*fac;
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iset++;
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return mean + std_dev*v2*fac;
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}
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unsigned char addnoise(int sym,double amp,double gain,double offset,int clip){
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int sample;
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sample = offset + gain*normal_rand(sym?amp:-amp,1.0);
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/* Clip to 8-bit offset range */
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if(sample < 0)
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sample = 0;
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else if(sample > clip)
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sample = clip;
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return sample;
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}
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