text: /* From: @(#)k_cos.c 1.3 95/01/18 */
  /*
   * ====================================================
   * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
   * Copyright (c) 2008 Steven G. Kargl, David Schultz, Bruce D. Evans.
   *
   * Developed at SunSoft, a Sun Microsystems, Inc. business.
   * Permission to use, copy, modify, and distribute this
   * software is freely granted, provided that this notice
   * is preserved.
   * ====================================================
   */
  
  #include <sys/cdefs.h>
  __FBSDID("$FreeBSD$");
  
  /*
   * ld80 version of k_cos.c.  See ../src/k_cos.c for most comments.
   */
  
  #include "math_private.h"
  
  /*
   * Domain [-0.7854, 0.7854], range ~[-2.43e-23, 2.425e-23]:
   * |cos(x) - c(x)| < 2**-75.1
   *
   * The coefficients of c(x) were generated by a pari-gp script using
   * a Remez algorithm that searches for the best higher coefficients
   * after rounding leading coefficients to a specified precision.
   *
   * Simpler methods like Chebyshev or basic Remez barely suffice for
   * cos() in 64-bit precision, because we want the coefficient of x^2
   * to be precisely -0.5 so that multiplying by it is exact, and plain
   * rounding of the coefficients of a good polynomial approximation only
   * gives this up to about 64-bit precision.  Plain rounding also gives
   * a mediocre approximation for the coefficient of x^4, but a rounding
   * error of 0.5 ulps for this coefficient would only contribute ~0.01
   * ulps to the final error, so this is unimportant.  Rounding errors in
   * higher coefficients are even less important.
   *
   * In fact, coefficients above the x^4 one only need to have 53-bit
   * precision, and this is more efficient.  We get this optimization
   * almost for free from the complications needed to search for the best
   * higher coefficients.
   */
  static const double
  one = 1.0;
  
  #if defined(__amd64__) || defined(__i386__)
  /* Long double constants are slow on these arches, and broken on i386. */
  static const volatile double
  C1hi = 0.041666666666666664,		/*  0x15555555555555.0p-57 */
  C1lo = 2.2598839032744733e-18;		/*  0x14d80000000000.0p-111 */
  #define	C1	((long double)C1hi + C1lo)
  #else
  static const long double
  C1 =  0.0416666666666666666136L;	/*  0xaaaaaaaaaaaaaa9b.0p-68 */
  #endif
  
  static const double
  C2 = -0.0013888888888888874,		/* -0x16c16c16c16c10.0p-62 */
  C3 =  0.000024801587301571716,		/*  0x1a01a01a018e22.0p-68 */
  C4 = -0.00000027557319215507120,	/* -0x127e4fb7602f22.0p-74 */
  C5 =  0.0000000020876754400407278,	/*  0x11eed8caaeccf1.0p-81 */
  C6 = -1.1470297442401303e-11,		/* -0x19393412bd1529.0p-89 */
  C7 =  4.7383039476436467e-14;		/*  0x1aac9d9af5c43e.0p-97 */
  
  long double
  __kernel_cosl(long double x, long double y)
  {
  	long double hz,z,r,w;
  
  	z  = x*x;
  	r  = z*(C1+z*(C2+z*(C3+z*(C4+z*(C5+z*(C6+z*C7))))));
  	hz = 0.5*z;
  	w  = one-hz;
  	return w + (((one-w)-hz) + (z*r-x*y));
  }
  