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head/lib/msun/ld80/e_powl.c
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svn:eol-style | null | native \ No newline at end of property |
svn:keywords | null | FreeBSD=%H \ No newline at end of property |
svn:mime-type | null | text/plain \ No newline at end of property |
/*- | |||||
* 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.c | |||||
* | |||||
* Power function, long double precision | |||||
* | |||||
* | |||||
* | |||||
* SYNOPSIS: | |||||
* | |||||
* long double x, y, z, powl(); | |||||
* | |||||
* z = powl( x, y ); | |||||
* | |||||
* | |||||
* | |||||
* DESCRIPTION: | |||||
* | |||||
* Computes x raised to the yth power. Analytically, | |||||
* | |||||
* x**y = exp( y log(x) ). | |||||
* | |||||
* Following Cody and Waite, this program uses a lookup table | |||||
* of 2**-i/32 and pseudo extended precision arithmetic to | |||||
* obtain several extra bits of accuracy in both the logarithm | |||||
* and the exponential. | |||||
* | |||||
* | |||||
* | |||||
* ACCURACY: | |||||
* | |||||
* The relative error of pow(x,y) can be estimated | |||||
* by y dl ln(2), where dl is the absolute error of | |||||
* the internally computed base 2 logarithm. At the ends | |||||
* of the approximation interval the logarithm equal 1/32 | |||||
* and its relative error is about 1 lsb = 1.1e-19. Hence | |||||
* the predicted relative error in the result is 2.3e-21 y . | |||||
* | |||||
* Relative error: | |||||
* arithmetic domain # trials peak rms | |||||
* | |||||
* IEEE +-1000 40000 2.8e-18 3.7e-19 | |||||
* .001 < x < 1000, with log(x) uniformly distributed. | |||||
* -1000 < y < 1000, y uniformly distributed. | |||||
* | |||||
* IEEE 0,8700 60000 6.5e-18 1.0e-18 | |||||
* 0.99 < x < 1.01, 0 < y < 8700, uniformly distributed. | |||||
* | |||||
* | |||||
* ERROR MESSAGES: | |||||
* | |||||
* message condition value returned | |||||
* pow overflow x**y > MAXNUM INFINITY | |||||
* pow underflow x**y < 1/MAXNUM 0.0 | |||||
* pow domain x<0 and y noninteger 0.0 | |||||
* | |||||
*/ | |||||
#include <sys/cdefs.h> | |||||
__FBSDID("$FreeBSD$"); | |||||
#include <float.h> | |||||
#include <math.h> | |||||
#include "math_private.h" | |||||
/* Table size */ | |||||
#define NXT 32 | |||||
/* log2(Table size) */ | |||||
#define LNXT 5 | |||||
/* log(1+x) = x - .5x^2 + x^3 * P(z)/Q(z) | |||||
* on the domain 2^(-1/32) - 1 <= x <= 2^(1/32) - 1 | |||||
*/ | |||||
static long double P[] = { | |||||
8.3319510773868690346226E-4L, | |||||
4.9000050881978028599627E-1L, | |||||
1.7500123722550302671919E0L, | |||||
1.4000100839971580279335E0L, | |||||
}; | |||||
static long double Q[] = { | |||||
/* 1.0000000000000000000000E0L,*/ | |||||
5.2500282295834889175431E0L, | |||||
8.4000598057587009834666E0L, | |||||
4.2000302519914740834728E0L, | |||||
}; | |||||
/* A[i] = 2^(-i/32), rounded to IEEE long double precision. | |||||
* If i is even, A[i] + B[i/2] gives additional accuracy. | |||||
*/ | |||||
static long double A[33] = { | |||||
1.0000000000000000000000E0L, | |||||
9.7857206208770013448287E-1L, | |||||
9.5760328069857364691013E-1L, | |||||
9.3708381705514995065011E-1L, | |||||
9.1700404320467123175367E-1L, | |||||
8.9735453750155359320742E-1L, | |||||
8.7812608018664974155474E-1L, | |||||
8.5930964906123895780165E-1L, | |||||
8.4089641525371454301892E-1L, | |||||
8.2287773907698242225554E-1L, | |||||
8.0524516597462715409607E-1L, | |||||
7.8799042255394324325455E-1L, | |||||
7.7110541270397041179298E-1L, | |||||
7.5458221379671136985669E-1L, | |||||
7.3841307296974965571198E-1L, | |||||
7.2259040348852331001267E-1L, | |||||
7.0710678118654752438189E-1L, | |||||
6.9195494098191597746178E-1L, | |||||
6.7712777346844636413344E-1L, | |||||
6.6261832157987064729696E-1L, | |||||
6.4841977732550483296079E-1L, | |||||
6.3452547859586661129850E-1L, | |||||
6.2092890603674202431705E-1L, | |||||
6.0762367999023443907803E-1L, | |||||
5.9460355750136053334378E-1L, | |||||
5.8186242938878875689693E-1L, | |||||
5.6939431737834582684856E-1L, | |||||
5.5719337129794626814472E-1L, | |||||
5.4525386633262882960438E-1L, | |||||
5.3357020033841180906486E-1L, | |||||
5.2213689121370692017331E-1L, | |||||
5.1094857432705833910408E-1L, | |||||
5.0000000000000000000000E-1L, | |||||
}; | |||||
static long double B[17] = { | |||||
0.0000000000000000000000E0L, | |||||
2.6176170809902549338711E-20L, | |||||
-1.0126791927256478897086E-20L, | |||||
1.3438228172316276937655E-21L, | |||||
1.2207982955417546912101E-20L, | |||||
-6.3084814358060867200133E-21L, | |||||
1.3164426894366316434230E-20L, | |||||
-1.8527916071632873716786E-20L, | |||||
1.8950325588932570796551E-20L, | |||||
1.5564775779538780478155E-20L, | |||||
6.0859793637556860974380E-21L, | |||||
-2.0208749253662532228949E-20L, | |||||
1.4966292219224761844552E-20L, | |||||
3.3540909728056476875639E-21L, | |||||
-8.6987564101742849540743E-22L, | |||||
-1.2327176863327626135542E-20L, | |||||
0.0000000000000000000000E0L, | |||||
}; | |||||
/* 2^x = 1 + x P(x), | |||||
* on the interval -1/32 <= x <= 0 | |||||
*/ | |||||
static long double R[] = { | |||||
1.5089970579127659901157E-5L, | |||||
1.5402715328927013076125E-4L, | |||||
1.3333556028915671091390E-3L, | |||||
9.6181291046036762031786E-3L, | |||||
5.5504108664798463044015E-2L, | |||||
2.4022650695910062854352E-1L, | |||||
6.9314718055994530931447E-1L, | |||||
}; | |||||
#define douba(k) A[k] | |||||
#define doubb(k) B[k] | |||||
#define MEXP (NXT*16384.0L) | |||||
/* The following if denormal numbers are supported, else -MEXP: */ | |||||
#define MNEXP (-NXT*(16384.0L+64.0L)) | |||||
/* log2(e) - 1 */ | |||||
#define LOG2EA 0.44269504088896340735992L | |||||
#define F W | |||||
#define Fa Wa | |||||
#define Fb Wb | |||||
#define G W | |||||
#define Ga Wa | |||||
#define Gb u | |||||
#define H W | |||||
#define Ha Wb | |||||
#define Hb Wb | |||||
static const long double MAXLOGL = 1.1356523406294143949492E4L; | |||||
static const long double MINLOGL = -1.13994985314888605586758E4L; | |||||
static const long double LOGE2L = 6.9314718055994530941723E-1L; | |||||
static volatile long double z; | |||||
static long double w, W, Wa, Wb, ya, yb, u; | |||||
static const long double huge = 0x1p10000L; | |||||
#if 0 /* XXX Prevent gcc from erroneously constant folding this. */ | |||||
static const long double twom10000 = 0x1p-10000L; | |||||
#else | |||||
static volatile long double twom10000 = 0x1p-10000L; | |||||
#endif | |||||
static long double reducl( long double ); | |||||
static long double powil ( long double, int ); | |||||
long double | |||||
powl(long double x, long double y) | |||||
{ | |||||
/* double F, Fa, Fb, G, Ga, Gb, H, Ha, Hb */ | |||||
int i, nflg, iyflg, yoddint; | |||||
long e; | |||||
if( y == 0.0L ) | |||||
return( 1.0L ); | |||||
if( x == 1.0L ) | |||||
return( 1.0L ); | |||||
if( isnan(x) ) | |||||
return( x ); | |||||
if( isnan(y) ) | |||||
return( y ); | |||||
if( y == 1.0L ) | |||||
return( x ); | |||||
if( !isfinite(y) && x == -1.0L ) | |||||
return( 1.0L ); | |||||
if( y >= LDBL_MAX ) | |||||
{ | |||||
if( x > 1.0L ) | |||||
return( INFINITY ); | |||||
if( x > 0.0L && x < 1.0L ) | |||||
return( 0.0L ); | |||||
if( x < -1.0L ) | |||||
return( INFINITY ); | |||||
if( x > -1.0L && x < 0.0L ) | |||||
return( 0.0L ); | |||||
} | |||||
if( y <= -LDBL_MAX ) | |||||
{ | |||||
if( x > 1.0L ) | |||||
return( 0.0L ); | |||||
if( x > 0.0L && x < 1.0L ) | |||||
return( INFINITY ); | |||||
if( x < -1.0L ) | |||||
return( 0.0L ); | |||||
if( x > -1.0L && x < 0.0L ) | |||||
return( INFINITY ); | |||||
} | |||||
if( x >= LDBL_MAX ) | |||||
{ | |||||
if( y > 0.0L ) | |||||
return( INFINITY ); | |||||
return( 0.0L ); | |||||
} | |||||
w = floorl(y); | |||||
/* Set iyflg to 1 if y is an integer. */ | |||||
iyflg = 0; | |||||
if( w == y ) | |||||
iyflg = 1; | |||||
/* Test for odd integer y. */ | |||||
yoddint = 0; | |||||
if( iyflg ) | |||||
{ | |||||
ya = fabsl(y); | |||||
ya = floorl(0.5L * ya); | |||||
yb = 0.5L * fabsl(w); | |||||
if( ya != yb ) | |||||
yoddint = 1; | |||||
} | |||||
if( x <= -LDBL_MAX ) | |||||
{ | |||||
if( y > 0.0L ) | |||||
{ | |||||
if( yoddint ) | |||||
return( -INFINITY ); | |||||
return( INFINITY ); | |||||
} | |||||
if( y < 0.0L ) | |||||
{ | |||||
if( yoddint ) | |||||
return( -0.0L ); | |||||
return( 0.0 ); | |||||
} | |||||
} | |||||
nflg = 0; /* flag = 1 if x<0 raised to integer power */ | |||||
if( x <= 0.0L ) | |||||
{ | |||||
if( x == 0.0L ) | |||||
{ | |||||
if( y < 0.0 ) | |||||
{ | |||||
if( signbit(x) && yoddint ) | |||||
return( -INFINITY ); | |||||
return( INFINITY ); | |||||
} | |||||
if( y > 0.0 ) | |||||
{ | |||||
if( signbit(x) && yoddint ) | |||||
return( -0.0L ); | |||||
return( 0.0 ); | |||||
} | |||||
if( y == 0.0L ) | |||||
return( 1.0L ); /* 0**0 */ | |||||
else | |||||
return( 0.0L ); /* 0**y */ | |||||
} | |||||
else | |||||
{ | |||||
if( iyflg == 0 ) | |||||
return (x - x) / (x - x); /* (x<0)**(non-int) is NaN */ | |||||
nflg = 1; | |||||
} | |||||
} | |||||
/* Integer power of an integer. */ | |||||
if( iyflg ) | |||||
{ | |||||
i = w; | |||||
w = floorl(x); | |||||
if( (w == x) && (fabsl(y) < 32768.0) ) | |||||
{ | |||||
w = powil( x, (int) y ); | |||||
return( w ); | |||||
} | |||||
} | |||||
if( nflg ) | |||||
x = fabsl(x); | |||||
/* separate significand from exponent */ | |||||
x = frexpl( x, &i ); | |||||
e = i; | |||||
/* find significand in antilog table A[] */ | |||||
i = 1; | |||||
if( x <= douba(17) ) | |||||
i = 17; | |||||
if( x <= douba(i+8) ) | |||||
i += 8; | |||||
if( x <= douba(i+4) ) | |||||
i += 4; | |||||
if( x <= douba(i+2) ) | |||||
i += 2; | |||||
if( x >= douba(1) ) | |||||
i = -1; | |||||
i += 1; | |||||
/* Find (x - A[i])/A[i] | |||||
* in order to compute log(x/A[i]): | |||||
* | |||||
* log(x) = log( a x/a ) = log(a) + log(x/a) | |||||
* | |||||
* log(x/a) = log(1+v), v = x/a - 1 = (x-a)/a | |||||
*/ | |||||
x -= douba(i); | |||||
x -= doubb(i/2); | |||||
x /= douba(i); | |||||
/* rational approximation for log(1+v): | |||||
* | |||||
* log(1+v) = v - v**2/2 + v**3 P(v) / Q(v) | |||||
*/ | |||||
z = x*x; | |||||
w = x * ( z * __polevll( x, P, 3 ) / __p1evll( x, Q, 3 ) ); | |||||
w = w - ldexpl( z, -1 ); /* w - 0.5 * z */ | |||||
/* Convert to base 2 logarithm: | |||||
* multiply by log2(e) = 1 + LOG2EA | |||||
*/ | |||||
z = LOG2EA * w; | |||||
z += w; | |||||
z += LOG2EA * x; | |||||
z += x; | |||||
/* Compute exponent term of the base 2 logarithm. */ | |||||
w = -i; | |||||
w = ldexpl( w, -LNXT ); /* divide by NXT */ | |||||
w += e; | |||||
/* Now base 2 log of x is w + z. */ | |||||
/* Multiply base 2 log by y, in extended precision. */ | |||||
/* separate y into large part ya | |||||
* and small part yb less than 1/NXT | |||||
*/ | |||||
ya = reducl(y); | |||||
yb = y - ya; | |||||
/* (w+z)(ya+yb) | |||||
* = w*ya + w*yb + z*y | |||||
*/ | |||||
F = z * y + w * yb; | |||||
Fa = reducl(F); | |||||
Fb = F - Fa; | |||||
G = Fa + w * ya; | |||||
Ga = reducl(G); | |||||
Gb = G - Ga; | |||||
H = Fb + Gb; | |||||
Ha = reducl(H); | |||||
w = ldexpl( Ga+Ha, LNXT ); | |||||
/* Test the power of 2 for overflow */ | |||||
if( w > MEXP ) | |||||
return (huge * huge); /* overflow */ | |||||
if( w < MNEXP ) | |||||
return (twom10000 * twom10000); /* underflow */ | |||||
e = w; | |||||
Hb = H - Ha; | |||||
if( Hb > 0.0L ) | |||||
{ | |||||
e += 1; | |||||
Hb -= (1.0L/NXT); /*0.0625L;*/ | |||||
} | |||||
/* Now the product y * log2(x) = Hb + e/NXT. | |||||
* | |||||
* Compute base 2 exponential of Hb, | |||||
* where -0.0625 <= Hb <= 0. | |||||
*/ | |||||
z = Hb * __polevll( Hb, R, 6 ); /* z = 2**Hb - 1 */ | |||||
/* Express e/NXT as an integer plus a negative number of (1/NXT)ths. | |||||
* Find lookup table entry for the fractional power of 2. | |||||
*/ | |||||
if( e < 0 ) | |||||
i = 0; | |||||
else | |||||
i = 1; | |||||
i = e/NXT + i; | |||||
e = NXT*i - e; | |||||
w = douba( e ); | |||||
z = w * z; /* 2**-e * ( 1 + (2**Hb-1) ) */ | |||||
z = z + w; | |||||
z = ldexpl( z, i ); /* multiply by integer power of 2 */ | |||||
if( nflg ) | |||||
{ | |||||
/* For negative x, | |||||
* find out if the integer exponent | |||||
* is odd or even. | |||||
*/ | |||||
w = ldexpl( y, -1 ); | |||||
w = floorl(w); | |||||
w = ldexpl( w, 1 ); | |||||
if( w != y ) | |||||
z = -z; /* odd exponent */ | |||||
} | |||||
return( z ); | |||||
} | |||||
/* Find a multiple of 1/NXT that is within 1/NXT of x. */ | |||||
static long double | |||||
reducl(long double x) | |||||
{ | |||||
long double t; | |||||
t = ldexpl( x, LNXT ); | |||||
t = floorl( t ); | |||||
t = ldexpl( t, -LNXT ); | |||||
return(t); | |||||
} | |||||
/* powil.c | |||||
* | |||||
* Real raised to integer power, long double precision | |||||
* | |||||
* | |||||
* | |||||
* SYNOPSIS: | |||||
* | |||||
* long double x, y, powil(); | |||||
* int n; | |||||
* | |||||
* y = powil( x, n ); | |||||
* | |||||
* | |||||
* | |||||
* DESCRIPTION: | |||||
* | |||||
* Returns argument x raised to the nth power. | |||||
* The routine efficiently decomposes n as a sum of powers of | |||||
* two. The desired power is a product of two-to-the-kth | |||||
* powers of x. Thus to compute the 32767 power of x requires | |||||
* 28 multiplications instead of 32767 multiplications. | |||||
* | |||||
* | |||||
* | |||||
* ACCURACY: | |||||
* | |||||
* | |||||
* Relative error: | |||||
* arithmetic x domain n domain # trials peak rms | |||||
* IEEE .001,1000 -1022,1023 50000 4.3e-17 7.8e-18 | |||||
* IEEE 1,2 -1022,1023 20000 3.9e-17 7.6e-18 | |||||
* IEEE .99,1.01 0,8700 10000 3.6e-16 7.2e-17 | |||||
* | |||||
* Returns MAXNUM on overflow, zero on underflow. | |||||
* | |||||
*/ | |||||
static long double | |||||
powil(long double x, int nn) | |||||
{ | |||||
long double ww, y; | |||||
long double s; | |||||
int n, e, sign, asign, lx; | |||||
if( x == 0.0L ) | |||||
{ | |||||
if( nn == 0 ) | |||||
return( 1.0L ); | |||||
else if( nn < 0 ) | |||||
return( LDBL_MAX ); | |||||
else | |||||
return( 0.0L ); | |||||
} | |||||
if( nn == 0 ) | |||||
return( 1.0L ); | |||||
if( x < 0.0L ) | |||||
{ | |||||
asign = -1; | |||||
x = -x; | |||||
} | |||||
else | |||||
asign = 0; | |||||
if( nn < 0 ) | |||||
{ | |||||
sign = -1; | |||||
n = -nn; | |||||
} | |||||
else | |||||
{ | |||||
sign = 1; | |||||
n = nn; | |||||
} | |||||
/* Overflow detection */ | |||||
/* Calculate approximate logarithm of answer */ | |||||
s = x; | |||||
s = frexpl( s, &lx ); | |||||
e = (lx - 1)*n; | |||||
if( (e == 0) || (e > 64) || (e < -64) ) | |||||
{ | |||||
s = (s - 7.0710678118654752e-1L) / (s + 7.0710678118654752e-1L); | |||||
s = (2.9142135623730950L * s - 0.5L + lx) * nn * LOGE2L; | |||||
} | |||||
else | |||||
{ | |||||
s = LOGE2L * e; | |||||
} | |||||
if( s > MAXLOGL ) | |||||
return (huge * huge); /* overflow */ | |||||
if( s < MINLOGL ) | |||||
return (twom10000 * twom10000); /* underflow */ | |||||
/* Handle tiny denormal answer, but with less accuracy | |||||
* since roundoff error in 1.0/x will be amplified. | |||||
* The precise demarcation should be the gradual underflow threshold. | |||||
*/ | |||||
if( s < (-MAXLOGL+2.0L) ) | |||||
{ | |||||
x = 1.0L/x; | |||||
sign = -sign; | |||||
} | |||||
/* First bit of the power */ | |||||
if( n & 1 ) | |||||
y = x; | |||||
else | |||||
{ | |||||
y = 1.0L; | |||||
asign = 0; | |||||
} | |||||
ww = x; | |||||
n >>= 1; | |||||
while( n ) | |||||
{ | |||||
ww = ww * ww; /* arg to the 2-to-the-kth power */ | |||||
if( n & 1 ) /* if that bit is set, then include in product */ | |||||
y *= ww; | |||||
n >>= 1; | |||||
} | |||||
if( asign ) | |||||
y = -y; /* odd power of negative number */ | |||||
if( sign < 0 ) | |||||
y = 1.0L/y; | |||||
return(y); | |||||
} |