24 lines
917 B
C
24 lines
917 B
C
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// DFT16.c
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// 16-point DFT
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// 12-bit binary fixed point
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#include <stdint.h>
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const int32_t ReW[16]={4096, 3784, 2896, 1567, 0, -1567, -2896, -3784, -4096, -3784, -2896, -1567, 0, 1567, 2896, 3784};
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const int32_t ImW[16]={0, -1567, -2896, -3784, -4096, -3784, -2896, -1567, 0, 1567, 2896, 3784, 4096, 3784, 2896, 1567};
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// 12-bit data*12-bit fixed*16 element, 12+12+4 = 28bit intermediate values, no overflow possible
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// units of ReX and ImX match units of x
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void DFT16(int32_t x[16],int32_t ReX[16],int32_t ImX[16]){
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ReX[0] = 0;
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for(int i=0; i<16; i++) ReX[0] += x[i];
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ReX[0] >>= 4; // matches units of x
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ImX[0] = 0; // real inputs
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for(int k=1; k<16; k++){
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ReX[k] = ImX[k] = 0;
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for(int n=0; n<16; n++){
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ReX[k] += x[n]*ReW[(k*n)&0x0F];
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ImX[k] += x[n]*ImW[(k*n)&0x0F];
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}
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ReX[k] >>= 15; // matches units of x
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ImX[k] >>= 15; // matches units of x
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}
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}
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