101 lines
2.7 KiB
C
101 lines
2.7 KiB
C
/*****************************************************************************/
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/*****************************************************************************/
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// atanf from musl-0.9.15
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/*****************************************************************************/
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/*****************************************************************************/
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/* origin: FreeBSD /usr/src/lib/msun/src/s_atanf.c */
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/*
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* Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
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*/
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/*
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* ====================================================
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* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
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*
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* Developed at SunPro, a Sun Microsystems, Inc. business.
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* Permission to use, copy, modify, and distribute this
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* software is freely granted, provided that this notice
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* is preserved.
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* ====================================================
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*/
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#include "libm.h"
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static const float atanhi[] = {
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4.6364760399e-01, /* atan(0.5)hi 0x3eed6338 */
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7.8539812565e-01, /* atan(1.0)hi 0x3f490fda */
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9.8279368877e-01, /* atan(1.5)hi 0x3f7b985e */
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1.5707962513e+00, /* atan(inf)hi 0x3fc90fda */
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};
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static const float atanlo[] = {
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5.0121582440e-09, /* atan(0.5)lo 0x31ac3769 */
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3.7748947079e-08, /* atan(1.0)lo 0x33222168 */
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3.4473217170e-08, /* atan(1.5)lo 0x33140fb4 */
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7.5497894159e-08, /* atan(inf)lo 0x33a22168 */
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};
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static const float aT[] = {
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3.3333328366e-01,
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-1.9999158382e-01,
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1.4253635705e-01,
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-1.0648017377e-01,
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6.1687607318e-02,
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};
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float atanf(float x)
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{
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float_t w,s1,s2,z;
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uint32_t ix,sign;
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int id;
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GET_FLOAT_WORD(ix, x);
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sign = ix>>31;
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ix &= 0x7fffffff;
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if (ix >= 0x4c800000) { /* if |x| >= 2**26 */
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if (isnan(x))
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return x;
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z = atanhi[3] + 0x1p-120f;
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return sign ? -z : z;
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}
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if (ix < 0x3ee00000) { /* |x| < 0.4375 */
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if (ix < 0x39800000) { /* |x| < 2**-12 */
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if (ix < 0x00800000)
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/* raise underflow for subnormal x */
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FORCE_EVAL(x*x);
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return x;
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}
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id = -1;
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} else {
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x = fabsf(x);
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if (ix < 0x3f980000) { /* |x| < 1.1875 */
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if (ix < 0x3f300000) { /* 7/16 <= |x| < 11/16 */
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id = 0;
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x = (2.0f*x - 1.0f)/(2.0f + x);
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} else { /* 11/16 <= |x| < 19/16 */
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id = 1;
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x = (x - 1.0f)/(x + 1.0f);
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}
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} else {
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if (ix < 0x401c0000) { /* |x| < 2.4375 */
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id = 2;
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x = (x - 1.5f)/(1.0f + 1.5f*x);
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} else { /* 2.4375 <= |x| < 2**26 */
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id = 3;
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x = -1.0f/x;
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}
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}
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}
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/* end of argument reduction */
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z = x*x;
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w = z*z;
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/* break sum from i=0 to 10 aT[i]z**(i+1) into odd and even poly */
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s1 = z*(aT[0]+w*(aT[2]+w*aT[4]));
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s2 = w*(aT[1]+w*aT[3]);
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if (id < 0)
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return x - x*(s1+s2);
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z = atanhi[id] - ((x*(s1+s2) - atanlo[id]) - x);
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return sign ? -z : z;
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}
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