1 | /* origin: FreeBSD /usr/src/lib/msun/src/e_atan2f.c */
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2 | /*
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3 | * Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
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4 | */
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5 | /*
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6 | * ====================================================
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7 | * Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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8 | *
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9 | * Developed at SunPro, a Sun Microsystems, Inc. business.
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10 | * Permission to use, copy, modify, and distribute this
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11 | * software is freely granted, provided that this notice
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12 | * is preserved.
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13 | * ====================================================
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14 | */
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15 |
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16 | #include "libm.h"
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17 |
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18 | static const float
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19 | pi = 3.1415927410e+00, /* 0x40490fdb */
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20 | pi_lo = -8.7422776573e-08; /* 0xb3bbbd2e */
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21 |
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22 | float atan2f(float y, float x)
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23 | {
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24 | float z;
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25 | uint32_t m,ix,iy;
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26 |
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27 | if (isnan(x) || isnan(y))
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28 | return x+y;
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29 | GET_FLOAT_WORD(ix, x);
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30 | GET_FLOAT_WORD(iy, y);
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31 | if (ix == 0x3f800000) /* x=1.0 */
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32 | return atanf(y);
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33 | m = ((iy>>31)&1) | ((ix>>30)&2); /* 2*sign(x)+sign(y) */
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34 | ix &= 0x7fffffff;
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35 | iy &= 0x7fffffff;
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36 |
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37 | /* when y = 0 */
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38 | if (iy == 0) {
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39 | switch (m) {
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40 | case 0:
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41 | case 1: return y; /* atan(+-0,+anything)=+-0 */
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42 | case 2: return pi; /* atan(+0,-anything) = pi */
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43 | case 3: return -pi; /* atan(-0,-anything) =-pi */
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44 | }
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45 | }
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46 | /* when x = 0 */
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47 | if (ix == 0)
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48 | return m&1 ? -pi/2 : pi/2;
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49 | /* when x is INF */
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50 | if (ix == 0x7f800000) {
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51 | if (iy == 0x7f800000) {
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52 | switch (m) {
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53 | case 0: return pi/4; /* atan(+INF,+INF) */
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54 | case 1: return -pi/4; /* atan(-INF,+INF) */
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55 | case 2: return 3*pi/4; /*atan(+INF,-INF)*/
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56 | case 3: return -3*pi/4; /*atan(-INF,-INF)*/
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57 | }
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58 | } else {
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59 | switch (m) {
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60 | case 0: return 0.0f; /* atan(+...,+INF) */
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61 | case 1: return -0.0f; /* atan(-...,+INF) */
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62 | case 2: return pi; /* atan(+...,-INF) */
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63 | case 3: return -pi; /* atan(-...,-INF) */
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64 | }
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65 | }
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66 | }
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67 | /* |y/x| > 0x1p26 */
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68 | if (ix+(26<<23) < iy || iy == 0x7f800000)
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69 | return m&1 ? -pi/2 : pi/2;
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70 |
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71 | /* z = atan(|y/x|) with correct underflow */
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72 | if ((m&2) && iy+(26<<23) < ix) /*|y/x| < 0x1p-26, x < 0 */
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73 | z = 0.0;
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74 | else
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75 | z = atanf(fabsf(y/x));
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76 | switch (m) {
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77 | case 0: return z; /* atan(+,+) */
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78 | case 1: return -z; /* atan(-,+) */
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79 | case 2: return pi - (z-pi_lo); /* atan(+,-) */
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80 | default: /* case 3 */
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81 | return (z-pi_lo) - pi; /* atan(-,-) */
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82 | }
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83 | }
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