72 lines
1.5 KiB
C
72 lines
1.5 KiB
C
/* origin: FreeBSD /usr/src/lib/msun/src/e_acosf.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 "libc/math/libm.h"
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static const float
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pio2_hi = 1.5707962513e+00, /* 0x3fc90fda */
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pio2_lo = 7.5497894159e-08, /* 0x33a22168 */
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pS0 = 1.6666586697e-01,
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pS1 = -4.2743422091e-02,
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pS2 = -8.6563630030e-03,
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qS1 = -7.0662963390e-01;
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static float R(float z)
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{
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float_t p, q;
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p = z*(pS0+z*(pS1+z*pS2));
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q = 1.0f+z*qS1;
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return p/q;
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}
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float acosf(float x)
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{
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float z,w,s,c,df;
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uint32_t hx,ix;
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GET_FLOAT_WORD(hx, x);
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ix = hx & 0x7fffffff;
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/* |x| >= 1 or nan */
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if (ix >= 0x3f800000) {
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if (ix == 0x3f800000) {
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if (hx >> 31)
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return 2*pio2_hi + 0x1p-120f;
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return 0;
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}
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return 0/(x-x);
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}
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/* |x| < 0.5 */
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if (ix < 0x3f000000) {
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if (ix <= 0x32800000) /* |x| < 2**-26 */
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return pio2_hi + 0x1p-120f;
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return pio2_hi - (x - (pio2_lo-x*R(x*x)));
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}
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/* x < -0.5 */
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if (hx >> 31) {
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z = (1+x)*0.5f;
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s = sqrtf(z);
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w = R(z)*s-pio2_lo;
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return 2*(pio2_hi - (s+w));
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}
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/* x > 0.5 */
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z = (1-x)*0.5f;
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s = sqrtf(z);
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GET_FLOAT_WORD(hx,s);
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SET_FLOAT_WORD(df,hx&0xfffff000);
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c = (z-df*df)/(s+df);
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w = R(z)*s+c;
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return 2*(df+w);
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}
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