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

     1  /* origin: FreeBSD /usr/src/lib/msun/src/e_acosf.c */
     2  /*
     3   * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
     4   */
     5  /*
     6   * ====================================================
     7   * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
     8   *
     9   * Developed at SunPro, a Sun Microsystems, Inc. business.
    10   * Permission to use, copy, modify, and distribute this
    11   * software is freely granted, provided that this notice
    12   * is preserved.
    13   * ====================================================
    14   */
    15  
    16  #include "libm.h"
    17  
    18  static const float
    19  pio2_hi = 1.5707962513e+00, /* 0x3fc90fda */
    20  pio2_lo = 7.5497894159e-08, /* 0x33a22168 */
    21  pS0 =  1.6666586697e-01,
    22  pS1 = -4.2743422091e-02,
    23  pS2 = -8.6563630030e-03,
    24  qS1 = -7.0662963390e-01;
    25  
    26  static float R(float z)
    27  {
    28  	float_t p, q;
    29  	p = z*(pS0+z*(pS1+z*pS2));
    30  	q = 1.0f+z*qS1;
    31  	return p/q;
    32  }
    33  
    34  float acosf(float x)
    35  {
    36  	float z,w,s,c,df;
    37  	uint32_t hx,ix;
    38  
    39  	GET_FLOAT_WORD(hx, x);
    40  	ix = hx & 0x7fffffff;
    41  	/* |x| >= 1 or nan */
    42  	if (ix >= 0x3f800000) {
    43  		if (ix == 0x3f800000) {
    44  			if (hx >> 31)
    45  				return 2*pio2_hi + 0x1p-120f;
    46  			return 0;
    47  		}
    48  		return 0/(x-x);
    49  	}
    50  	/* |x| < 0.5 */
    51  	if (ix < 0x3f000000) {
    52  		if (ix <= 0x32800000) /* |x| < 2**-26 */
    53  			return pio2_hi + 0x1p-120f;
    54  		return pio2_hi - (x - (pio2_lo-x*R(x*x)));
    55  	}
    56  	/* x < -0.5 */
    57  	if (hx >> 31) {
    58  		z = (1+x)*0.5f;
    59  		s = sqrtf(z);
    60  		w = R(z)*s-pio2_lo;
    61  		return 2*(pio2_hi - (s+w));
    62  	}
    63  	/* x > 0.5 */
    64  	z = (1-x)*0.5f;
    65  	s = sqrtf(z);
    66  	GET_FLOAT_WORD(hx,s);
    67  	SET_FLOAT_WORD(df,hx&0xfffff000);
    68  	c = (z-df*df)/(s+df);
    69  	w = R(z)*s+c;
    70  	return 2*(df+w);
    71  }