ref: 8898df42f669d4140fa5404e615bf048356437f6
dir: /src/mixer/ft2_windowed_sinc.c/
#include <stdint.h> #include <stdbool.h> #include <stdlib.h> #include <math.h> #include "ft2_windowed_sinc.h" // globalized double *gKaiserSinc = NULL; double *gDownSample1 = NULL; double *gDownSample2 = NULL; /* Code taken from the OpenMPT project, which has a BSD ** license which is compatible with this this project. ** ** The code has been slightly modified. */ static double Izero(double y) // Compute Bessel function Izero(y) using a series approximation { double s = 1.0, ds = 1.0, d = 0.0; const double epsilon = 1E-9; // 8bb: 1E-7 -> 1E-9 for added precision (still fast to calculate) do { d = d + 2.0; ds = ds * (y * y) / (d * d); s = s + ds; } while (ds > epsilon * s); return s; } static void getSinc(double *dLUTPtr, const double beta, const double cutoff) { const double izeroBeta = Izero(beta); const double kPi = 4.0 * atan(1.0) * cutoff; // M_PI can't be trusted for (int32_t i = 0; i < SINC_LUT_LEN; i++) { double dSinc; int32_t ix = (SINC_TAPS-1) - (i & (SINC_TAPS-1)); ix = (ix * SINC_PHASES) + (i >> SINC_TAPS_BITS); if (ix == SINC_MID_TAP) { dSinc = 1.0; } else { const double x = (ix - SINC_MID_TAP) * (1.0 / SINC_PHASES); const double xPi = x * kPi; const double xMul = 1.0 / ((SINC_TAPS/2) * (SINC_TAPS/2)); dSinc = sin(xPi) * Izero(beta * sqrt(1.0 - x * x * xMul)) / (izeroBeta * xPi); // Kaiser window } dLUTPtr[i] = dSinc * cutoff; } } bool calcWindowedSincTables(void) { gKaiserSinc = (double *)malloc(SINC_LUT_LEN * sizeof (double)); gDownSample1 = (double *)malloc(SINC_LUT_LEN * sizeof (double)); gDownSample2 = (double *)malloc(SINC_LUT_LEN * sizeof (double)); if (gKaiserSinc == NULL || gDownSample1 == NULL || gDownSample2 == NULL) return false; // OpenMPT parameters getSinc(gKaiserSinc, 9.6377, 0.97); getSinc(gDownSample1, 8.5, 0.5); getSinc(gDownSample2, 2.7625, 0.425); return true; } void freeWindowedSincTables(void) { if (gKaiserSinc != NULL) { free(gKaiserSinc); gKaiserSinc = NULL; } if (gDownSample1 != NULL) { free(gDownSample1); gDownSample1 = NULL; } if (gDownSample2 != NULL) { free(gDownSample2); gDownSample2 = NULL; } }