diff options
Diffstat (limited to 'system/lib/libc/musl/src/math/tgammal.c')
| -rw-r--r-- | system/lib/libc/musl/src/math/tgammal.c | 275 |
1 files changed, 275 insertions, 0 deletions
diff --git a/system/lib/libc/musl/src/math/tgammal.c b/system/lib/libc/musl/src/math/tgammal.c new file mode 100644 index 00000000..5c1a02a6 --- /dev/null +++ b/system/lib/libc/musl/src/math/tgammal.c @@ -0,0 +1,275 @@ +/* origin: OpenBSD /usr/src/lib/libm/src/ld80/e_tgammal.c */ +/* + * 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. + */ +/* + * Gamma function + * + * + * SYNOPSIS: + * + * long double x, y, tgammal(); + * + * y = tgammal( x ); + * + * + * DESCRIPTION: + * + * Returns gamma function of the argument. The result is + * correctly signed. + * + * Arguments |x| <= 13 are reduced by recurrence and the function + * approximated by a rational function of degree 7/8 in the + * interval (2,3). Large arguments are handled by Stirling's + * formula. Large negative arguments are made positive using + * a reflection formula. + * + * + * ACCURACY: + * + * Relative error: + * arithmetic domain # trials peak rms + * IEEE -40,+40 10000 3.6e-19 7.9e-20 + * IEEE -1755,+1755 10000 4.8e-18 6.5e-19 + * + * Accuracy for large arguments is dominated by error in powl(). + * + */ + +#include "libm.h" + +#if LDBL_MANT_DIG == 53 && LDBL_MAX_EXP == 1024 +long double tgammal(long double x) +{ + return tgamma(x); +} +#elif LDBL_MANT_DIG == 64 && LDBL_MAX_EXP == 16384 +/* +tgamma(x+2) = tgamma(x+2) P(x)/Q(x) +0 <= x <= 1 +Relative error +n=7, d=8 +Peak error = 1.83e-20 +Relative error spread = 8.4e-23 +*/ +static const long double P[8] = { + 4.212760487471622013093E-5L, + 4.542931960608009155600E-4L, + 4.092666828394035500949E-3L, + 2.385363243461108252554E-2L, + 1.113062816019361559013E-1L, + 3.629515436640239168939E-1L, + 8.378004301573126728826E-1L, + 1.000000000000000000009E0L, +}; +static const long double Q[9] = { +-1.397148517476170440917E-5L, + 2.346584059160635244282E-4L, +-1.237799246653152231188E-3L, +-7.955933682494738320586E-4L, + 2.773706565840072979165E-2L, +-4.633887671244534213831E-2L, +-2.243510905670329164562E-1L, + 4.150160950588455434583E-1L, + 9.999999999999999999908E-1L, +}; + +/* +static const long double P[] = { +-3.01525602666895735709e0L, +-3.25157411956062339893e1L, +-2.92929976820724030353e2L, +-1.70730828800510297666e3L, +-7.96667499622741999770e3L, +-2.59780216007146401957e4L, +-5.99650230220855581642e4L, +-7.15743521530849602425e4L +}; +static const long double Q[] = { + 1.00000000000000000000e0L, +-1.67955233807178858919e1L, + 8.85946791747759881659e1L, + 5.69440799097468430177e1L, +-1.98526250512761318471e3L, + 3.31667508019495079814e3L, + 1.60577839621734713377e4L, +-2.97045081369399940529e4L, +-7.15743521530849602412e4L +}; +*/ +#define MAXGAML 1755.455L +/*static const long double LOGPI = 1.14472988584940017414L;*/ + +/* Stirling's formula for the gamma function +tgamma(x) = sqrt(2 pi) x^(x-.5) exp(-x) (1 + 1/x P(1/x)) +z(x) = x +13 <= x <= 1024 +Relative error +n=8, d=0 +Peak error = 9.44e-21 +Relative error spread = 8.8e-4 +*/ +static const long double STIR[9] = { + 7.147391378143610789273E-4L, +-2.363848809501759061727E-5L, +-5.950237554056330156018E-4L, + 6.989332260623193171870E-5L, + 7.840334842744753003862E-4L, +-2.294719747873185405699E-4L, +-2.681327161876304418288E-3L, + 3.472222222230075327854E-3L, + 8.333333333333331800504E-2L, +}; + +#define MAXSTIR 1024.0L +static const long double SQTPI = 2.50662827463100050242E0L; + +/* 1/tgamma(x) = z P(z) + * z(x) = 1/x + * 0 < x < 0.03125 + * Peak relative error 4.2e-23 + */ +static const long double S[9] = { +-1.193945051381510095614E-3L, + 7.220599478036909672331E-3L, +-9.622023360406271645744E-3L, +-4.219773360705915470089E-2L, + 1.665386113720805206758E-1L, +-4.200263503403344054473E-2L, +-6.558780715202540684668E-1L, + 5.772156649015328608253E-1L, + 1.000000000000000000000E0L, +}; + +/* 1/tgamma(-x) = z P(z) + * z(x) = 1/x + * 0 < x < 0.03125 + * Peak relative error 5.16e-23 + * Relative error spread = 2.5e-24 + */ +static const long double SN[9] = { + 1.133374167243894382010E-3L, + 7.220837261893170325704E-3L, + 9.621911155035976733706E-3L, +-4.219773343731191721664E-2L, +-1.665386113944413519335E-1L, +-4.200263503402112910504E-2L, + 6.558780715202536547116E-1L, + 5.772156649015328608727E-1L, +-1.000000000000000000000E0L, +}; + +static const long double PIL = 3.1415926535897932384626L; + +/* Gamma function computed by Stirling's formula. + */ +static long double stirf(long double x) +{ + long double y, w, v; + + w = 1.0/x; + /* For large x, use rational coefficients from the analytical expansion. */ + if (x > 1024.0) + w = (((((6.97281375836585777429E-5L * w + + 7.84039221720066627474E-4L) * w + - 2.29472093621399176955E-4L) * w + - 2.68132716049382716049E-3L) * w + + 3.47222222222222222222E-3L) * w + + 8.33333333333333333333E-2L) * w + + 1.0; + else + w = 1.0 + w * __polevll(w, STIR, 8); + y = expl(x); + if (x > MAXSTIR) { /* Avoid overflow in pow() */ + v = powl(x, 0.5L * x - 0.25L); + y = v * (v / y); + } else { + y = powl(x, x - 0.5L) / y; + } + y = SQTPI * y * w; + return y; +} + +long double tgammal(long double x) +{ + long double p, q, z; + + if (!isfinite(x)) + return x + INFINITY; + + q = fabsl(x); + if (q > 13.0) { + if (x < 0.0) { + p = floorl(q); + z = q - p; + if (z == 0) + return 0 / z; + if (q > MAXGAML) { + z = 0; + } else { + if (z > 0.5) { + p += 1.0; + z = q - p; + } + z = q * sinl(PIL * z); + z = fabsl(z) * stirf(q); + z = PIL/z; + } + if (0.5 * p == floorl(q * 0.5)) + z = -z; + } else if (x > MAXGAML) { + z = x * 0x1p16383L; + } else { + z = stirf(x); + } + return z; + } + + z = 1.0; + while (x >= 3.0) { + x -= 1.0; + z *= x; + } + while (x < -0.03125L) { + z /= x; + x += 1.0; + } + if (x <= 0.03125L) + goto small; + while (x < 2.0) { + z /= x; + x += 1.0; + } + if (x == 2.0) + return z; + + x -= 2.0; + p = __polevll(x, P, 7); + q = __polevll(x, Q, 8); + z = z * p / q; + return z; + +small: + /* z==1 if x was originally +-0 */ + if (x == 0 && z != 1) + return x / x; + if (x < 0.0) { + x = -x; + q = z / (x * __polevll(x, SN, 8)); + } else + q = z / (x * __polevll(x, S, 8)); + return q; +} +#endif |