[352] | 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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