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OpenLibm/ld128/e_powl.c
Viral B. Shah 52c901a68c Import long double versions from OpenBSD.
2014-12-04 23:11:16 +05:30

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/*
* ====================================================
* 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.
* ====================================================
*/
/*
* Copyright (c) 2008 Stephen L. Moshier <steve@moshier.net>
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
/* powl(x,y) return x**y
*
* n
* Method: Let x = 2 * (1+f)
* 1. Compute and return log2(x) in two pieces:
* log2(x) = w1 + w2,
* where w1 has 113-53 = 60 bit trailing zeros.
* 2. Perform y*log2(x) = n+y' by simulating muti-precision
* arithmetic, where |y'|<=0.5.
* 3. Return x**y = 2**n*exp(y'*log2)
*
* Special cases:
* 1. (anything) ** 0 is 1
* 2. (anything) ** 1 is itself
* 3. (anything) ** NAN is NAN
* 4. NAN ** (anything except 0) is NAN
* 5. +-(|x| > 1) ** +INF is +INF
* 6. +-(|x| > 1) ** -INF is +0
* 7. +-(|x| < 1) ** +INF is +0
* 8. +-(|x| < 1) ** -INF is +INF
* 9. +-1 ** +-INF is NAN
* 10. +0 ** (+anything except 0, NAN) is +0
* 11. -0 ** (+anything except 0, NAN, odd integer) is +0
* 12. +0 ** (-anything except 0, NAN) is +INF
* 13. -0 ** (-anything except 0, NAN, odd integer) is +INF
* 14. -0 ** (odd integer) = -( +0 ** (odd integer) )
* 15. +INF ** (+anything except 0,NAN) is +INF
* 16. +INF ** (-anything except 0,NAN) is +0
* 17. -INF ** (anything) = -0 ** (-anything)
* 18. (-anything) ** (integer) is (-1)**(integer)*(+anything**integer)
* 19. (-anything except 0 and inf) ** (non-integer) is NAN
*
*/
#include <math.h>
#include "math_private.h"
static const long double bp[] = {
1.0L,
1.5L,
};
/* log_2(1.5) */
static const long double dp_h[] = {
0.0,
5.8496250072115607565592654282227158546448E-1L
};
/* Low part of log_2(1.5) */
static const long double dp_l[] = {
0.0,
1.0579781240112554492329533686862998106046E-16L
};
static const long double zero = 0.0L,
one = 1.0L,
two = 2.0L,
two113 = 1.0384593717069655257060992658440192E34L,
huge = 1.0e3000L,
tiny = 1.0e-3000L;
/* 3/2 log x = 3 z + z^3 + z^3 (z^2 R(z^2))
z = (x-1)/(x+1)
1 <= x <= 1.25
Peak relative error 2.3e-37 */
static const long double LN[] =
{
-3.0779177200290054398792536829702930623200E1L,
6.5135778082209159921251824580292116201640E1L,
-4.6312921812152436921591152809994014413540E1L,
1.2510208195629420304615674658258363295208E1L,
-9.9266909031921425609179910128531667336670E-1L
};
static const long double LD[] =
{
-5.129862866715009066465422805058933131960E1L,
1.452015077564081884387441590064272782044E2L,
-1.524043275549860505277434040464085593165E2L,
7.236063513651544224319663428634139768808E1L,
-1.494198912340228235853027849917095580053E1L
/* 1.0E0 */
};
/* exp(x) = 1 + x - x / (1 - 2 / (x - x^2 R(x^2)))
0 <= x <= 0.5
Peak relative error 5.7e-38 */
static const long double PN[] =
{
5.081801691915377692446852383385968225675E8L,
9.360895299872484512023336636427675327355E6L,
4.213701282274196030811629773097579432957E4L,
5.201006511142748908655720086041570288182E1L,
9.088368420359444263703202925095675982530E-3L,
};
static const long double PD[] =
{
3.049081015149226615468111430031590411682E9L,
1.069833887183886839966085436512368982758E8L,
8.259257717868875207333991924545445705394E5L,
1.872583833284143212651746812884298360922E3L,
/* 1.0E0 */
};
static const long double
/* ln 2 */
lg2 = 6.9314718055994530941723212145817656807550E-1L,
lg2_h = 6.9314718055994528622676398299518041312695E-1L,
lg2_l = 2.3190468138462996154948554638754786504121E-17L,
ovt = 8.0085662595372944372e-0017L,
/* 2/(3*log(2)) */
cp = 9.6179669392597560490661645400126142495110E-1L,
cp_h = 9.6179669392597555432899980587535537779331E-1L,
cp_l = 5.0577616648125906047157785230014751039424E-17L;
long double
powl(long double x, long double y)
{
long double z, ax, z_h, z_l, p_h, p_l;
long double yy1, t1, t2, r, s, t, u, v, w;
long double s2, s_h, s_l, t_h, t_l;
int32_t i, j, k, yisint, n;
u_int32_t ix, iy;
int32_t hx, hy;
ieee_quad_shape_type o, p, q;
p.value = x;
hx = p.parts32.mswhi;
ix = hx & 0x7fffffff;
q.value = y;
hy = q.parts32.mswhi;
iy = hy & 0x7fffffff;
/* y==zero: x**0 = 1 */
if ((iy | q.parts32.mswlo | q.parts32.lswhi | q.parts32.lswlo) == 0)
return one;
/* 1.0**y = 1; -1.0**+-Inf = 1 */
if (x == one)
return one;
if (x == -1.0L && iy == 0x7fff0000
&& (q.parts32.mswlo | q.parts32.lswhi | q.parts32.lswlo) == 0)
return one;
/* +-NaN return x+y */
if ((ix > 0x7fff0000)
|| ((ix == 0x7fff0000)
&& ((p.parts32.mswlo | p.parts32.lswhi | p.parts32.lswlo) != 0))
|| (iy > 0x7fff0000)
|| ((iy == 0x7fff0000)
&& ((q.parts32.mswlo | q.parts32.lswhi | q.parts32.lswlo) != 0)))
return x + y;
/* determine if y is an odd int when x < 0
* yisint = 0 ... y is not an integer
* yisint = 1 ... y is an odd int
* yisint = 2 ... y is an even int
*/
yisint = 0;
if (hx < 0)
{
if (iy >= 0x40700000) /* 2^113 */
yisint = 2; /* even integer y */
else if (iy >= 0x3fff0000) /* 1.0 */
{
if (floorl (y) == y)
{
z = 0.5 * y;
if (floorl (z) == z)
yisint = 2;
else
yisint = 1;
}
}
}
/* special value of y */
if ((q.parts32.mswlo | q.parts32.lswhi | q.parts32.lswlo) == 0)
{
if (iy == 0x7fff0000) /* y is +-inf */
{
if (((ix - 0x3fff0000) | p.parts32.mswlo | p.parts32.lswhi |
p.parts32.lswlo) == 0)
return y - y; /* +-1**inf is NaN */
else if (ix >= 0x3fff0000) /* (|x|>1)**+-inf = inf,0 */
return (hy >= 0) ? y : zero;
else /* (|x|<1)**-,+inf = inf,0 */
return (hy < 0) ? -y : zero;
}
if (iy == 0x3fff0000)
{ /* y is +-1 */
if (hy < 0)
return one / x;
else
return x;
}
if (hy == 0x40000000)
return x * x; /* y is 2 */
if (hy == 0x3ffe0000)
{ /* y is 0.5 */
if (hx >= 0) /* x >= +0 */
return sqrtl (x);
}
}
ax = fabsl (x);
/* special value of x */
if ((p.parts32.mswlo | p.parts32.lswhi | p.parts32.lswlo) == 0)
{
if (ix == 0x7fff0000 || ix == 0 || ix == 0x3fff0000)
{
z = ax; /*x is +-0,+-inf,+-1 */
if (hy < 0)
z = one / z; /* z = (1/|x|) */
if (hx < 0)
{
if (((ix - 0x3fff0000) | yisint) == 0)
{
z = (z - z) / (z - z); /* (-1)**non-int is NaN */
}
else if (yisint == 1)
z = -z; /* (x<0)**odd = -(|x|**odd) */
}
return z;
}
}
/* (x<0)**(non-int) is NaN */
if (((((u_int32_t) hx >> 31) - 1) | yisint) == 0)
return (x - x) / (x - x);
/* |y| is huge.
2^-16495 = 1/2 of smallest representable value.
If (1 - 1/131072)^y underflows, y > 1.4986e9 */
if (iy > 0x401d654b)
{
/* if (1 - 2^-113)^y underflows, y > 1.1873e38 */
if (iy > 0x407d654b)
{
if (ix <= 0x3ffeffff)
return (hy < 0) ? huge * huge : tiny * tiny;
if (ix >= 0x3fff0000)
return (hy > 0) ? huge * huge : tiny * tiny;
}
/* over/underflow if x is not close to one */
if (ix < 0x3ffeffff)
return (hy < 0) ? huge * huge : tiny * tiny;
if (ix > 0x3fff0000)
return (hy > 0) ? huge * huge : tiny * tiny;
}
n = 0;
/* take care subnormal number */
if (ix < 0x00010000)
{
ax *= two113;
n -= 113;
o.value = ax;
ix = o.parts32.mswhi;
}
n += ((ix) >> 16) - 0x3fff;
j = ix & 0x0000ffff;
/* determine interval */
ix = j | 0x3fff0000; /* normalize ix */
if (j <= 0x3988)
k = 0; /* |x|<sqrt(3/2) */
else if (j < 0xbb67)
k = 1; /* |x|<sqrt(3) */
else
{
k = 0;
n += 1;
ix -= 0x00010000;
}
o.value = ax;
o.parts32.mswhi = ix;
ax = o.value;
/* compute s = s_h+s_l = (x-1)/(x+1) or (x-1.5)/(x+1.5) */
u = ax - bp[k]; /* bp[0]=1.0, bp[1]=1.5 */
v = one / (ax + bp[k]);
s = u * v;
s_h = s;
o.value = s_h;
o.parts32.lswlo = 0;
o.parts32.lswhi &= 0xf8000000;
s_h = o.value;
/* t_h=ax+bp[k] High */
t_h = ax + bp[k];
o.value = t_h;
o.parts32.lswlo = 0;
o.parts32.lswhi &= 0xf8000000;
t_h = o.value;
t_l = ax - (t_h - bp[k]);
s_l = v * ((u - s_h * t_h) - s_h * t_l);
/* compute log(ax) */
s2 = s * s;
u = LN[0] + s2 * (LN[1] + s2 * (LN[2] + s2 * (LN[3] + s2 * LN[4])));
v = LD[0] + s2 * (LD[1] + s2 * (LD[2] + s2 * (LD[3] + s2 * (LD[4] + s2))));
r = s2 * s2 * u / v;
r += s_l * (s_h + s);
s2 = s_h * s_h;
t_h = 3.0 + s2 + r;
o.value = t_h;
o.parts32.lswlo = 0;
o.parts32.lswhi &= 0xf8000000;
t_h = o.value;
t_l = r - ((t_h - 3.0) - s2);
/* u+v = s*(1+...) */
u = s_h * t_h;
v = s_l * t_h + t_l * s;
/* 2/(3log2)*(s+...) */
p_h = u + v;
o.value = p_h;
o.parts32.lswlo = 0;
o.parts32.lswhi &= 0xf8000000;
p_h = o.value;
p_l = v - (p_h - u);
z_h = cp_h * p_h; /* cp_h+cp_l = 2/(3*log2) */
z_l = cp_l * p_h + p_l * cp + dp_l[k];
/* log2(ax) = (s+..)*2/(3*log2) = n + dp_h + z_h + z_l */
t = (long double) n;
t1 = (((z_h + z_l) + dp_h[k]) + t);
o.value = t1;
o.parts32.lswlo = 0;
o.parts32.lswhi &= 0xf8000000;
t1 = o.value;
t2 = z_l - (((t1 - t) - dp_h[k]) - z_h);
/* s (sign of result -ve**odd) = -1 else = 1 */
s = one;
if (((((u_int32_t) hx >> 31) - 1) | (yisint - 1)) == 0)
s = -one; /* (-ve)**(odd int) */
/* split up y into yy1+y2 and compute (yy1+y2)*(t1+t2) */
yy1 = y;
o.value = yy1;
o.parts32.lswlo = 0;
o.parts32.lswhi &= 0xf8000000;
yy1 = o.value;
p_l = (y - yy1) * t1 + y * t2;
p_h = yy1 * t1;
z = p_l + p_h;
o.value = z;
j = o.parts32.mswhi;
if (j >= 0x400d0000) /* z >= 16384 */
{
/* if z > 16384 */
if (((j - 0x400d0000) | o.parts32.mswlo | o.parts32.lswhi |
o.parts32.lswlo) != 0)
return s * huge * huge; /* overflow */
else
{
if (p_l + ovt > z - p_h)
return s * huge * huge; /* overflow */
}
}
else if ((j & 0x7fffffff) >= 0x400d01b9) /* z <= -16495 */
{
/* z < -16495 */
if (((j - 0xc00d01bc) | o.parts32.mswlo | o.parts32.lswhi |
o.parts32.lswlo)
!= 0)
return s * tiny * tiny; /* underflow */
else
{
if (p_l <= z - p_h)
return s * tiny * tiny; /* underflow */
}
}
/* compute 2**(p_h+p_l) */
i = j & 0x7fffffff;
k = (i >> 16) - 0x3fff;
n = 0;
if (i > 0x3ffe0000)
{ /* if |z| > 0.5, set n = [z+0.5] */
n = floorl (z + 0.5L);
t = n;
p_h -= t;
}
t = p_l + p_h;
o.value = t;
o.parts32.lswlo = 0;
o.parts32.lswhi &= 0xf8000000;
t = o.value;
u = t * lg2_h;
v = (p_l - (t - p_h)) * lg2 + t * lg2_l;
z = u + v;
w = v - (z - u);
/* exp(z) */
t = z * z;
u = PN[0] + t * (PN[1] + t * (PN[2] + t * (PN[3] + t * PN[4])));
v = PD[0] + t * (PD[1] + t * (PD[2] + t * (PD[3] + t)));
t1 = z - t * u / v;
r = (z * t1) / (t1 - two) - (w + z * w);
z = one - (r - z);
o.value = z;
j = o.parts32.mswhi;
j += (n << 16);
if ((j >> 16) <= 0)
z = scalbnl (z, n); /* subnormal output */
else
{
o.parts32.mswhi = j;
z = o.value;
}
return s * z;
}
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