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/* dlngam.f -- translated by f2c (version 20041007).
You must link the resulting object file with libf2c:
on Microsoft Windows system, link with libf2c.lib;
on Linux or Unix systems, link with .../path/to/libf2c.a -lm
or, if you install libf2c.a in a standard place, with -lf2c -lm
-- in that order, at the end of the command line, as in
cc *.o -lf2c -lm
Source for libf2c is in /netlib/f2c/libf2c.zip, e.g.,
http://www.netlib.org/f2c/libf2c.zip
*/
/** This routine has been editted to be thread safe **/
#define V3P_NETLIB_SRC
#include "v3p_netlib.h"
/* Table of constant values */
static integer c__2 = 2;
static integer c__4 = 4;
static integer c__3 = 3;
static integer c__1 = 1;
/* DECK DLNGAM */
doublereal dlngam_(doublereal *x)
{
/* Initialized data */
static doublereal sq2pil = .91893853320467274178032973640562;
static doublereal sqpi2l = .225791352644727432363097614947441;
static doublereal pi = 3.1415926535897932384626433832795;
// static logical first = TRUE_;
/* System generated locals */
doublereal ret_val = 0.0, d__1, d__2;
/* Builtin functions */
double log(doublereal), sqrt(doublereal), sin(doublereal), d_int(
doublereal *);
/* Local variables */
doublereal y, temp;
/* static */ doublereal xmax, dxrel;
extern doublereal d1mach_(integer *), d9lgmc_(doublereal *), dgamma_(
doublereal *);
extern /* Subroutine */ int xermsg_(char *, char *, char *, integer *,
integer *, ftnlen, ftnlen, ftnlen);
doublereal sinpiy;
/* ***BEGIN PROLOGUE DLNGAM */
/* ***PURPOSE Compute the logarithm of the absolute value of the Gamma */
/* function. */
/* ***LIBRARY SLATEC (FNLIB) */
/* ***CATEGORY C7A */
/* ***TYPE DOUBLE PRECISION (ALNGAM-S, DLNGAM-D, CLNGAM-C) */
/* ***KEYWORDS ABSOLUTE VALUE, COMPLETE GAMMA FUNCTION, FNLIB, LOGARITHM, */
/* SPECIAL FUNCTIONS */
/* ***AUTHOR Fullerton, W., (LANL) */
/* ***DESCRIPTION */
/* DLNGAM(X) calculates the double precision logarithm of the */
/* absolute value of the Gamma function for double precision */
/* argument X. */
/* ***REFERENCES (NONE) */
/* ***ROUTINES CALLED D1MACH, D9LGMC, DGAMMA, XERMSG */
/* ***REVISION HISTORY (YYMMDD) */
/* 770601 DATE WRITTEN */
/* 890531 Changed all specific intrinsics to generic. (WRB) */
/* 890531 REVISION DATE from Version 3.2 */
/* 891214 Prologue converted to Version 4.0 format. (BAB) */
/* 900315 CALLs to XERROR changed to CALLs to XERMSG. (THJ) */
/* 900727 Added EXTERNAL statement. (WRB) */
/* ***END PROLOGUE DLNGAM */
/* ***FIRST EXECUTABLE STATEMENT DLNGAM */
// d1mach has been made thread safe, so there is no need for the
// statics in determining these values
// if (first) {
// temp = 1. / log(d1mach_(&c__2));
// xmax = temp * d1mach_(&c__2);
// dxrel = sqrt(d1mach_(&c__4));
// }
// first = FALSE_;
temp = 1. / log(d1mach_(&c__2));
xmax = temp * d1mach_(&c__2);
dxrel = sqrt(d1mach_(&c__4));
y = abs(*x);
if (y > 10.) {
goto L20;
}
/* LOG (ABS (DGAMMA(X)) ) FOR ABS(X) .LE. 10.0 */
ret_val = log((d__1 = dgamma_(x), abs(d__1)));
return ret_val;
/* LOG ( ABS (DGAMMA(X)) ) FOR ABS(X) .GT. 10.0 */
L20:
if (y > xmax) {
xermsg_("SLATEC", "DLNGAM", "ABS(X) SO BIG DLNGAM OVERFLOWS", &c__2, &
c__2, (ftnlen)6, (ftnlen)6, (ftnlen)30);
}
if (*x > 0.) {
ret_val = sq2pil + (*x - .5) * log(*x) - *x + d9lgmc_(&y);
}
if (*x > 0.) {
return ret_val;
}
sinpiy = (d__1 = sin(pi * y), abs(d__1));
if (sinpiy == 0.) {
xermsg_("SLATEC", "DLNGAM", "X IS A NEGATIVE INTEGER", &c__3, &c__2, (
ftnlen)6, (ftnlen)6, (ftnlen)23);
}
d__2 = *x - .5;
if ((d__1 = (*x - d_int(&d__2)) / *x, abs(d__1)) < dxrel) {
xermsg_("SLATEC", "DLNGAM", "ANSWER LT HALF PRECISION BECAUSE X TOO "
"NEAR NEGATIVE INTEGER", &c__1, &c__1, (ftnlen)6, (ftnlen)6, (
ftnlen)60);
}
ret_val = sqpi2l + (*x - .5) * log(y) - *x - log(sinpiy) - d9lgmc_(&y);
return ret_val;
} /* dlngam_ */
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