ref: fa8fc530f8604c935804008cec6e2c89702c6f18
dir: /src/mixer/ft2_cubic.c/
#include <stdint.h> #include <stdbool.h> #include <stdlib.h> #include "ft2_cubic.h" float *fCubicLUT8 = NULL; float *fCubicLUT16 = NULL; /* 4-tap cubic spline interpolation (Horner's method) ** ** This simplified LUT formula has been used in several trackers, but ** I think it originates from ModPlug Tracker (not sure about this). */ static void calcCubicLUT(float *fLUTPtr, const double dSale) { for (int32_t i = 0; i < CUBIC_PHASES; i++) { const double x = i * (1.0 / CUBIC_PHASES); const double x2 = x * x; // x^2 const double x3 = x2 * x; // x^3 *fLUTPtr++ = (float)((-0.5 * x3 + 1.0 * x2 - 0.5 * x) * dSale); *fLUTPtr++ = (float)(( 1.5 * x3 - 2.5 * x2 + 1.0) * dSale); *fLUTPtr++ = (float)((-1.5 * x3 + 2.0 * x2 + 0.5 * x) * dSale); *fLUTPtr++ = (float)(( 0.5 * x3 - 0.5 * x2) * dSale); } } bool calcCubicTable(void) { fCubicLUT8 = (float *)malloc(CUBIC_LUT_LEN * sizeof (float)); if (fCubicLUT8 == NULL) return false; fCubicLUT16 = (float *)malloc(CUBIC_LUT_LEN * sizeof (float)); if (fCubicLUT16 == NULL) return false; calcCubicLUT(fCubicLUT8, 1.0 / 128.0); // for 8-bit samples calcCubicLUT(fCubicLUT16, 1.0 / 32768.0); // for 16-bit samples return true; } void freeCubicTable(void) { if (fCubicLUT8 != NULL) { free(fCubicLUT8); fCubicLUT8 = NULL; } if (fCubicLUT16 != NULL) { free(fCubicLUT16); fCubicLUT16 = NULL; } }