fusl/src/math/__cosdf.c

/* origin: FreeBSD /usr/src/lib/msun/src/k_cosf.c */
/*
 * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
 * Debugged and optimized by Bruce D. Evans.
 */
/*
 * ====================================================
 * 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.
 * ====================================================
 */

#include "libm.h"

/* |cos(x) - c(x)| < 2**-34.1 (~[-5.37e-11, 5.295e-11]). */
static const double C0 = -0x1ffffffd0c5e81.0p-54, /* -0.499999997251031003120 */
    C1 = 0x155553e1053a42.0p-57,  /*  0.0416666233237390631894 */
    C2 = -0x16c087e80f1e27.0p-62, /* -0.00138867637746099294692 */
    C3 = 0x199342e0ee5069.0p-68;  /*  0.0000243904487962774090654 */

float __cosdf(double x) {
  double_t r, w, z;

  /* Try to optimize for parallel evaluation as in __tandf.c. */
  z = x * x;
  w = z * z;
  r = C2 + z * C3;
  return ((1.0 + z * C0) + w * C1) + (w * z) * r;
}