fusl/src/math/sincos.c

/* origin: FreeBSD /usr/src/lib/msun/src/s_sin.c */
/*
 * ====================================================
 * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
 *
 * Developed at SunPro, a Sun Microsystems, Inc. business.
 * Permission to use, copy, modify, and distribute this
 * software is freely granted, provided that this notice
 * is preserved.
 * ====================================================
 */

#define _GNU_SOURCE
#include "libm.h"

void sincos(double x, double* sin, double* cos) {
  double y[2], s, c;
  uint32_t ix;
  unsigned n;

  GET_HIGH_WORD(ix, x);
  ix &= 0x7fffffff;

  /* |x| ~< pi/4 */
  if (ix <= 0x3fe921fb) {
    /* if |x| < 2**-27 * sqrt(2) */
    if (ix < 0x3e46a09e) {
      /* raise inexact if x!=0 and underflow if subnormal */
      FORCE_EVAL(ix < 0x00100000 ? x / 0x1p120f : x + 0x1p120f);
      *sin = x;
      *cos = 1.0;
      return;
    }
    *sin = __sin(x, 0.0, 0);
    *cos = __cos(x, 0.0);
    return;
  }

  /* sincos(Inf or NaN) is NaN */
  if (ix >= 0x7ff00000) {
    *sin = *cos = x - x;
    return;
  }

  /* argument reduction needed */
  n = __rem_pio2(x, y);
  s = __sin(y[0], y[1], 1);
  c = __cos(y[0], y[1]);
  switch (n & 3) {
    case 0:
      *sin = s;
      *cos = c;
      break;
    case 1:
      *sin = c;
      *cos = -s;
      break;
    case 2:
      *sin = -s;
      *cos = -c;
      break;
    case 3:
    default:
      *sin = -c;
      *cos = s;
      break;
  }
}