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math: rewrite inverse hyperbolic functions to be simpler/smaller

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modifications:
* avoid unsigned->signed integer conversion
* do not handle special cases when they work correctly anyway
* more strict threshold values (0x1p26 instead of 0x1p28 etc)
* smaller code, cleaner branching logic
* same precision as the old code:
    acosh(x) has up to 2ulp error in [1,1.125]
    asinh(x) has up to 1.6ulp error in [0.125,0.5], [-0.5,-0.125]
    atanh(x) has up to 1.7ulp error in [0.125,0.5], [-0.5,-0.125]
This commit is contained in:
Szabolcs Nagy
2012-12-11 23:06:20 +01:00
parent 64623cd59a
commit 482ccd2f74
9 changed files with 149 additions and 406 deletions
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72
src/math/asinhl.c
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@ -1,25 +1,3 @@
/* origin: OpenBSD /usr/src/lib/libm/src/ld80/s_asinhl.c */
/*
* ====================================================
* 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.
* ====================================================
*/
/* asinhl(x)
* Method :
* Based on
* asinhl(x) = signl(x) * logl [ |x| + sqrtl(x*x+1) ]
* we have
* asinhl(x) := x if 1+x*x=1,
* := signl(x)*(logl(x)+ln2)) for large |x|, else
* := signl(x)*logl(2|x|+1/(|x|+sqrtl(x*x+1))) if|x|>2, else
* := signl(x)*log1pl(|x| + x^2/(1 + sqrtl(1+x^2)))
*/
#include "libm.h"
#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024
@ -28,35 +6,33 @@ long double asinhl(long double x)
return asinh(x);
}
#elif LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384
static const long double
ln2 = 6.931471805599453094287e-01L, /* 0x3FFE, 0xB17217F7, 0xD1CF79AC */
huge = 1.000000000000000000e+4900L;
/* asinh(x) = sign(x)*log(|x|+sqrt(x*x+1)) ~= x - x^3/6 + o(x^5) */
long double asinhl(long double x)
{
long double t,w;
int32_t hx,ix;
union {
long double f;
struct{uint64_t m; uint16_t se; uint16_t pad;} i;
} u = {.f = x};
unsigned e = u.i.se & 0x7fff;
unsigned s = u.i.se >> 15;
GET_LDOUBLE_EXP(hx, x);
ix = hx & 0x7fff;
if (ix == 0x7fff)
return x + x; /* x is inf or NaN */
if (ix < 0x3fde) { /* |x| < 2**-34 */
/* return x, raise inexact if x != 0 */
if (huge+x > 1.0)
return x;
/* |x| */
u.i.se = e;
x = u.f;
if (e >= 0x3fff + 32) {
/* |x| >= 0x1p32 or inf or nan */
x = logl(x) + 0.693147180559945309417232121458176568L;
} else if (e >= 0x3fff + 1) {
/* |x| >= 2 */
x = logl(2*x + 1/(sqrtl(x*x+1)+x));
} else if (e >= 0x3fff - 32) {
/* |x| >= 0x1p-32 */
x = log1pl(x + x*x/(sqrtl(x*x+1)+1));
} else {
/* |x| < 0x1p-32, raise inexact if x!=0 */
FORCE_EVAL(x + 0x1p1000);
}
if (ix > 0x4020) { /* |x| > 2**34 */
w = logl(fabsl(x)) + ln2;
} else if (ix > 0x4000) { /* 2**34 > |x| > 2.0 */
t = fabsl(x);
w = logl(2.0*t + 1.0/(sqrtl(x*x + 1.0) + t));
} else { /* 2.0 > |x| > 2**-28 */
t = x*x;
w =log1pl(fabsl(x) + t/(1.0 + sqrtl(1.0 + t)));
}
if (hx & 0x8000)
return -w;
return w;
return s ? -x : x;
}
#endif