github.com/afumu/libc@v0.0.6/musl/src/math/acosl.c (about)

     1  /* origin: FreeBSD /usr/src/lib/msun/src/e_acosl.c */
     2  /*
     3   * ====================================================
     4   * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
     5   *
     6   * Developed at SunSoft, a Sun Microsystems, Inc. business.
     7   * Permission to use, copy, modify, and distribute this
     8   * software is freely granted, provided that this notice
     9   * is preserved.
    10   * ====================================================
    11   */
    12  /*
    13   * See comments in acos.c.
    14   * Converted to long double by David Schultz <das@FreeBSD.ORG>.
    15   */
    16  
    17  #include "libm.h"
    18  
    19  #if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
    20  long double acosl(long double x)
    21  {
    22  	return acos(x);
    23  }
    24  #elif (LDBL_MANT_DIG == 64 || LDBL_MANT_DIG == 113) && LDBL_MAX_EXP == 16384
    25  #include "__invtrigl.h"
    26  #if LDBL_MANT_DIG == 64
    27  #define CLEARBOTTOM(u) (u.i.m &= -1ULL << 32)
    28  #elif LDBL_MANT_DIG == 113
    29  #define CLEARBOTTOM(u) (u.i.lo = 0)
    30  #endif
    31  
    32  long double acosl(long double x)
    33  {
    34  	union ldshape u = {x};
    35  	long double z, s, c, f;
    36  	uint16_t e = u.i.se & 0x7fff;
    37  
    38  	/* |x| >= 1 or nan */
    39  	if (e >= 0x3fff) {
    40  		if (x == 1)
    41  			return 0;
    42  		if (x == -1)
    43  			return 2*pio2_hi + 0x1p-120f;
    44  		return 0/(x-x);
    45  	}
    46  	/* |x| < 0.5 */
    47  	if (e < 0x3fff - 1) {
    48  		if (e < 0x3fff - LDBL_MANT_DIG - 1)
    49  			return pio2_hi + 0x1p-120f;
    50  		return pio2_hi - (__invtrigl_R(x*x)*x - pio2_lo + x);
    51  	}
    52  	/* x < -0.5 */
    53  	if (u.i.se >> 15) {
    54  		z = (1 + x)*0.5;
    55  		s = sqrtl(z);
    56  		return 2*(pio2_hi - (__invtrigl_R(z)*s - pio2_lo + s));
    57  	}
    58  	/* x > 0.5 */
    59  	z = (1 - x)*0.5;
    60  	s = sqrtl(z);
    61  	u.f = s;
    62  	CLEARBOTTOM(u);
    63  	f = u.f;
    64  	c = (z - f*f)/(s + f);
    65  	return 2*(__invtrigl_R(z)*s + c + f);
    66  }
    67  #endif