fixmath.h

/*
 * Fixed point type.
 * Based on Allegro library by Shawn Hargreaves.
 */

#ifndef FIXMATH_FIXMATH_H
#define FIXMATH_FIXMATH_H

#include "base/ints.h"
#include <cerrno>

namespace fixmath {

  typedef int32_t fixed;

  extern const fixed fixtorad_r;
  extern const fixed radtofix_r;

  extern fixed _cos_tbl[];
  extern fixed _tan_tbl[];
  extern fixed _acos_tbl[];

  fixed fixsqrt(fixed x);
  fixed fixhypot(fixed x, fixed y);
  fixed fixatan(fixed x);
  fixed fixatan2(fixed y, fixed x);

  // ftofix and fixtof are used in generic C versions of fixmul and fixdiv
  inline fixed ftofix(double x) {
    if (x > 32767.0) {
      errno = ERANGE;
      return 0x7FFFFFFF;
    }

    if (x < -32767.0) {
      errno = ERANGE;
      return -0x7FFFFFFF;
    }

    return (fixed)(x * 65536.0 + (x < 0 ? -0.5 : 0.5));
  }

  inline double fixtof(fixed x) {
    return (double)x / 65536.0;
  };

  inline fixed fixadd(fixed x, fixed y) {
    fixed result = x + y;

    if (result >= 0) {
      if ((x < 0) && (y < 0)) {
        errno = ERANGE;
        return -0x7FFFFFFF;
      }
      return result;
    }
    if ((x > 0) && (y > 0)) {
      errno = ERANGE;
      return 0x7FFFFFFF;
    }
    return result;
  }

  inline fixed fixsub(fixed x, fixed y) {
    fixed result = x - y;

    if (result >= 0) {
      if ((x < 0) && (y > 0)) {
        errno = ERANGE;
        return -0x7FFFFFFF;
      }
      return result;
    }
    if ((x > 0) && (y < 0)) {
      errno = ERANGE;
      return 0x7FFFFFFF;
    }
    return result;
  }

  inline fixed fixmul(fixed x, fixed y) {
    return ftofix(fixtof(x) * fixtof(y));
  }

  inline fixed fixdiv(fixed x, fixed y) {
    if (y == 0) {
      errno = ERANGE;
      return (x < 0) ? -0x7FFFFFFF : 0x7FFFFFFF;
    }
    return ftofix(fixtof(x) / fixtof(y));
  }

  inline int fixfloor(fixed x) {
    /* (x >> 16) is not portable */
    if (x >= 0)
      return (x >> 16);
    return ~((~x) >> 16);
  }

  inline int fixceil(fixed x) {
    if (x > 0x7FFF0000) {
      errno = ERANGE;
      return 0x7FFF;
    }

    return fixfloor(x + 0xFFFF);
  }

  inline fixed itofix(int x) {
    return x << 16;
  }

  inline int fixtoi(fixed x) {
    return fixfloor(x) + ((x & 0x8000) >> 15);
  }

  inline fixed fixcos(fixed x) {
    return _cos_tbl[((x + 0x4000) >> 15) & 0x1FF];
  }

  inline fixed fixsin(fixed x) {
    return _cos_tbl[((x - 0x400000 + 0x4000) >> 15) & 0x1FF];
  }

  inline fixed fixtan(fixed x) {
    return _tan_tbl[((x + 0x4000) >> 15) & 0xFF];
  }

  inline fixed fixacos(fixed x) {
    if ((x < -65536) || (x > 65536)) {
      errno = EDOM;
      return 0;
    }

    return _acos_tbl[(x+65536+127)>>8];
  }

  inline fixed fixasin(fixed x) {
    if ((x < -65536) || (x > 65536)) {
      errno = EDOM;
      return 0;
    }

    return 0x00400000 - _acos_tbl[(x+65536+127)>>8];
  }

} // namespace fixmath

#endif