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Justine Tunney 2020-06-15 07:18:57 -07:00
commit c91b3c5006
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libc/math/acosf.c Normal file
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/* origin: FreeBSD /usr/src/lib/msun/src/e_acosf.c */
/*
* Conversion to float by Ian Lance Taylor, Cygnus Support, ian@cygnus.com.
*/
/*
* ====================================================
* Copyright (C) 1993 by Sun Microsystems, Inc. All rights reserved.
*
* Developed at SunPro, a Sun Microsystems, Inc. business.
* Permission to use, copy, modify, and distribute this
* software is freely granted, provided that this notice
* is preserved.
* ====================================================
*/
#include "libc/math/libm.h"
static const float
pio2_hi = 1.5707962513e+00, /* 0x3fc90fda */
pio2_lo = 7.5497894159e-08, /* 0x33a22168 */
pS0 = 1.6666586697e-01,
pS1 = -4.2743422091e-02,
pS2 = -8.6563630030e-03,
qS1 = -7.0662963390e-01;
static float R(float z)
{
float_t p, q;
p = z*(pS0+z*(pS1+z*pS2));
q = 1.0f+z*qS1;
return p/q;
}
float acosf(float x)
{
float z,w,s,c,df;
uint32_t hx,ix;
GET_FLOAT_WORD(hx, x);
ix = hx & 0x7fffffff;
/* |x| >= 1 or nan */
if (ix >= 0x3f800000) {
if (ix == 0x3f800000) {
if (hx >> 31)
return 2*pio2_hi + 0x1p-120f;
return 0;
}
return 0/(x-x);
}
/* |x| < 0.5 */
if (ix < 0x3f000000) {
if (ix <= 0x32800000) /* |x| < 2**-26 */
return pio2_hi + 0x1p-120f;
return pio2_hi - (x - (pio2_lo-x*R(x*x)));
}
/* x < -0.5 */
if (hx >> 31) {
z = (1+x)*0.5f;
s = sqrtf(z);
w = R(z)*s-pio2_lo;
return 2*(pio2_hi - (s+w));
}
/* x > 0.5 */
z = (1-x)*0.5f;
s = sqrtf(z);
GET_FLOAT_WORD(hx,s);
SET_FLOAT_WORD(df,hx&0xfffff000);
c = (z-df*df)/(s+df);
w = R(z)*s+c;
return 2*(df+w);
}