github.com/afumu/libc@v0.0.6/musl/src/math/atan2f.c (about)

     1  /* origin: FreeBSD /usr/src/lib/msun/src/e_atan2f.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  pi     = 3.1415927410e+00, /* 0x40490fdb */
    20  pi_lo  = -8.7422776573e-08; /* 0xb3bbbd2e */
    21  
    22  float atan2f(float y, float x)
    23  {
    24  	float z;
    25  	uint32_t m,ix,iy;
    26  
    27  	if (isnan(x) || isnan(y))
    28  		return x+y;
    29  	GET_FLOAT_WORD(ix, x);
    30  	GET_FLOAT_WORD(iy, y);
    31  	if (ix == 0x3f800000)  /* x=1.0 */
    32  		return atanf(y);
    33  	m = ((iy>>31)&1) | ((ix>>30)&2);  /* 2*sign(x)+sign(y) */
    34  	ix &= 0x7fffffff;
    35  	iy &= 0x7fffffff;
    36  
    37  	/* when y = 0 */
    38  	if (iy == 0) {
    39  		switch (m) {
    40  		case 0:
    41  		case 1: return y;   /* atan(+-0,+anything)=+-0 */
    42  		case 2: return  pi; /* atan(+0,-anything) = pi */
    43  		case 3: return -pi; /* atan(-0,-anything) =-pi */
    44  		}
    45  	}
    46  	/* when x = 0 */
    47  	if (ix == 0)
    48  		return m&1 ? -pi/2 : pi/2;
    49  	/* when x is INF */
    50  	if (ix == 0x7f800000) {
    51  		if (iy == 0x7f800000) {
    52  			switch (m) {
    53  			case 0: return  pi/4; /* atan(+INF,+INF) */
    54  			case 1: return -pi/4; /* atan(-INF,+INF) */
    55  			case 2: return 3*pi/4;  /*atan(+INF,-INF)*/
    56  			case 3: return -3*pi/4; /*atan(-INF,-INF)*/
    57  			}
    58  		} else {
    59  			switch (m) {
    60  			case 0: return  0.0f;    /* atan(+...,+INF) */
    61  			case 1: return -0.0f;    /* atan(-...,+INF) */
    62  			case 2: return  pi; /* atan(+...,-INF) */
    63  			case 3: return -pi; /* atan(-...,-INF) */
    64  			}
    65  		}
    66  	}
    67  	/* |y/x| > 0x1p26 */
    68  	if (ix+(26<<23) < iy || iy == 0x7f800000)
    69  		return m&1 ? -pi/2 : pi/2;
    70  
    71  	/* z = atan(|y/x|) with correct underflow */
    72  	if ((m&2) && iy+(26<<23) < ix)  /*|y/x| < 0x1p-26, x < 0 */
    73  		z = 0.0;
    74  	else
    75  		z = atanf(fabsf(y/x));
    76  	switch (m) {
    77  	case 0: return z;              /* atan(+,+) */
    78  	case 1: return -z;             /* atan(-,+) */
    79  	case 2: return pi - (z-pi_lo); /* atan(+,-) */
    80  	default: /* case 3 */
    81  		return (z-pi_lo) - pi; /* atan(-,-) */
    82  	}
    83  }