MicroDexed/sin.h

/*
   Copyright 2012 Google Inc.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

        http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

class Sin {
  public:
    Sin();

    static void init();
    static int32_t lookup(int32_t phase);
    static int32_t compute(int32_t phase);

    // A more accurate sine, both input and output Q30
    static int32_t compute10(int32_t phase);
};

#define SIN_LG_N_SAMPLES 10
#define SIN_N_SAMPLES (1 << SIN_LG_N_SAMPLES)

#define SIN_INLINE

// Use twice as much RAM for the LUT but avoid a little computation
#define SIN_DELTA

#ifdef SIN_DELTA
extern int32_t sintab[SIN_N_SAMPLES << 1];
#else
extern int32_t sintab[SIN_N_SAMPLES + 1];
#endif

#ifdef SIN_INLINE
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 = sintab[phase_int];
  int y0 = 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 = sintab[phase_int];
  int y1 = sintab[phase_int + 1];

  return y0 + (((int64_t)(y1 - y0) * (int64_t)lowbits) >> SHIFT);
#endif
}
#endif