ref: d69c1cb37c0b88febe74656feeaa067cc09f9add
dir: /libcelt/plc.c/
#ifndef NEW_PLC #define NEW_PLC #endif float _celt_lpc( float *lpc, /* out: [0...p-1] LPC coefficients */ const float *ac, /* in: [0...p] autocorrelation values */ int p ) { int i, j; float r; float error = ac[0]; if (ac[0] == 0) { for (i = 0; i < p; i++) lpc[i] = 0; return 0; } for (i = 0; i < p; i++) { /* Sum up this iteration's reflection coefficient */ float rr = -ac[i + 1]; for (j = 0; j < i; j++) rr = rr - lpc[j]*ac[i - j]; r = rr/(error+1e-15); /* Update LPC coefficients and total error */ lpc[i] = r; for (j = 0; j < i>>1; j++) { float tmp = lpc[j]; lpc[j] = lpc[j ] + r*lpc[i-1-j]; lpc[i-1-j] = lpc[i-1-j] + r*tmp; } if (i & 1) lpc[j] = lpc[j] + lpc[j]*r; error = error - r*r*error; if (error<.00001*ac[0]) break; } return error; } void fir(const float *x, const float *num, float *y, int N, int ord, float *mem) { int i,j; for (i=0;i<N;i++) { float sum = x[i]; for (j=0;j<ord;j++) { sum += num[j]*mem[j]; } for (j=ord-1;j>=1;j--) { mem[j]=mem[j-1]; } mem[0] = x[i]; y[i] = sum; } } void iir(const celt_word32 *x, const float *den, celt_word32 *y, int N, int ord, float *mem) { int i,j; for (i=0;i<N;i++) { float sum = x[i]; for (j=0;j<ord;j++) { sum -= den[j]*mem[j]; } for (j=ord-1;j>=1;j--) { mem[j]=mem[j-1]; } mem[0] = sum; y[i] = sum; } } void _celt_autocorr( const float *x, /* in: [0...n-1] samples x */ float *ac, /* out: [0...lag-1] ac values */ const celt_word16 *window, int overlap, int lag, int n ) { float d; int i; VARDECL(float, xx); SAVE_STACK; ALLOC(xx, n, float); for (i=0;i<n;i++) xx[i] = x[i]; for (i=0;i<overlap;i++) { xx[i] *= (1./Q15ONE)*window[i]; xx[n-i-1] *= (1./Q15ONE)*window[i]; } while (lag>=0) { for (i = lag, d = 0; i < n; i++) d += x[i] * x[i-lag]; ac[lag] = d; lag--; } ac[0] += 10; RESTORE_STACK; }