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

     1  /* origin: FreeBSD /usr/src/lib/msun/src/s_cosf.c */
     2  /*
     3   * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
     4   * Optimized by Bruce D. Evans.
     5   */
     6  /*
     7   * ====================================================
     8   * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
     9   *
    10   * Developed at SunPro, a Sun Microsystems, Inc. business.
    11   * Permission to use, copy, modify, and distribute this
    12   * software is freely granted, provided that this notice
    13   * is preserved.
    14   * ====================================================
    15   */
    16  
    17  #include "libm.h"
    18  
    19  /* Small multiples of pi/2 rounded to double precision. */
    20  static const double
    21  c1pio2 = 1*M_PI_2, /* 0x3FF921FB, 0x54442D18 */
    22  c2pio2 = 2*M_PI_2, /* 0x400921FB, 0x54442D18 */
    23  c3pio2 = 3*M_PI_2, /* 0x4012D97C, 0x7F3321D2 */
    24  c4pio2 = 4*M_PI_2; /* 0x401921FB, 0x54442D18 */
    25  
    26  float cosf(float x)
    27  {
    28  	double y;
    29  	uint32_t ix;
    30  	unsigned n, sign;
    31  
    32  	GET_FLOAT_WORD(ix, x);
    33  	sign = ix >> 31;
    34  	ix &= 0x7fffffff;
    35  
    36  	if (ix <= 0x3f490fda) {  /* |x| ~<= pi/4 */
    37  		if (ix < 0x39800000) {  /* |x| < 2**-12 */
    38  			/* raise inexact if x != 0 */
    39  			FORCE_EVAL(x + 0x1p120f);
    40  			return 1.0f;
    41  		}
    42  		return __cosdf(x);
    43  	}
    44  	if (ix <= 0x407b53d1) {  /* |x| ~<= 5*pi/4 */
    45  		if (ix > 0x4016cbe3)  /* |x|  ~> 3*pi/4 */
    46  			return -__cosdf(sign ? x+c2pio2 : x-c2pio2);
    47  		else {
    48  			if (sign)
    49  				return __sindf(x + c1pio2);
    50  			else
    51  				return __sindf(c1pio2 - x);
    52  		}
    53  	}
    54  	if (ix <= 0x40e231d5) {  /* |x| ~<= 9*pi/4 */
    55  		if (ix > 0x40afeddf)  /* |x| ~> 7*pi/4 */
    56  			return __cosdf(sign ? x+c4pio2 : x-c4pio2);
    57  		else {
    58  			if (sign)
    59  				return __sindf(-x - c3pio2);
    60  			else
    61  				return __sindf(x - c3pio2);
    62  		}
    63  	}
    64  
    65  	/* cos(Inf or NaN) is NaN */
    66  	if (ix >= 0x7f800000)
    67  		return x-x;
    68  
    69  	/* general argument reduction needed */
    70  	n = __rem_pio2f(x,&y);
    71  	switch (n&3) {
    72  	case 0: return  __cosdf(y);
    73  	case 1: return  __sindf(-y);
    74  	case 2: return -__cosdf(y);
    75  	default:
    76  		return  __sindf(y);
    77  	}
    78  }