math_lut.h

 
#pragma once
 
#include "engine.h"
 
// Use twice as much RAM for the LUT but avoid a little computation
#define SIN_DELTA
 
void dx_init_lut_data();
 
class Exp2 {
public:
    // Q24 in, Q24 out
    static int32_t lookup(int32_t x);
};
 
inline int32_t Exp2::lookup(int32_t x) {
    const int SHIFT = 24 - EXP2_LG_N_SAMPLES;
    int lowbits = x & ((1 << SHIFT) - 1);
    int x_int = (x >> (SHIFT - 1)) & ((EXP2_N_SAMPLES - 1) << 1);
    int dy = dxEngine->exp2tab[x_int];
    int y0 = dxEngine->exp2tab[x_int + 1];
 
    int y = y0 + (((int64_t)dy * (int64_t)lowbits) >> SHIFT);
    return y >> (6 - (x >> 24));
}
 
class Tanh {
public:
    // Q24 in, Q24 out
    static int32_t lookup(int32_t x);
};
 
inline int32_t Tanh::lookup(int32_t x) {
    int32_t signum = x >> 31;
    x ^= signum;
    if (x >= (4 << 24)) {
        if (x >= (17 << 23)) {
            return signum ^ (1 << 24);
        }
        int32_t sx = ((int64_t)-48408812 * (int64_t)x) >> 24;
        return signum ^ ((1 << 24) - 2 * Exp2::lookup(sx));
    }
    else {
        const int SHIFT = 26 - TANH_LG_N_SAMPLES;
        int lowbits = x & ((1 << SHIFT) - 1);
        int x_int = (x >> (SHIFT - 1)) & ((TANH_N_SAMPLES - 1) << 1);
        int dy = dxEngine->tanhtab[x_int];
        int y0 = dxEngine->tanhtab[x_int + 1];
        int y = y0 + (((int64_t)dy * (int64_t)lowbits) >> SHIFT);
        return y ^ signum;
    }
}
 
class Sin {
public:
    static int32_t lookup(int32_t phase);
};
 
inline int32_t Sin::lookup(int32_t phase) {
    const int SHIFT = 24 - SIN_LG_N_SAMPLES;
    int lowbits = phase & ((1 << SHIFT) - 1);
#ifdef SIN_DELTA
    int phase_int = (phase >> (SHIFT - 1)) & ((SIN_N_SAMPLES - 1) << 1);
    int dy = dxEngine->sintab[phase_int];
    int y0 = dxEngine->sintab[phase_int + 1];
 
    return y0 + (((int64_t)dy * (int64_t)lowbits) >> SHIFT);
#else
    int phase_int = (phase >> SHIFT) & (SIN_N_SAMPLES - 1);
    int y0 = dxEngine->sintab[phase_int];
    int y1 = dxEngine->sintab[phase_int + 1];
 
    return y0 + (((int64_t)(y1 - y0) * (int64_t)lowbits) >> SHIFT);
#endif
}
 
class Freqlut {
public:
    static int32_t lookup(int32_t logfreq);
};