Question

我正在浏览函数gamma()的R源代码，该代码指向this C source file。

代码片段如下：

#ifdef NOMORE_FOR_THREADS
    static int ngam = 0;
    static double xmin = 0, xmax = 0., xsml = 0., dxrel = 0.;

    /* Initialize machine dependent constants, the first time gamma() is called.
    FIXME for threads ! */
    if (ngam == 0) {
    ngam = chebyshev_init(gamcs, 42, DBL_EPSILON/20);/*was .1*d1mach(3)*/
    gammalims(&xmin, &xmax);/*-> ./gammalims.c */
    xsml = exp(fmax2(log(DBL_MIN), -log(DBL_MAX)) + 0.01);
    /*   = exp(.01)*DBL_MIN = 2.247e-308 for IEEE */
    dxrel = sqrt(DBL_EPSILON);/*was sqrt(d1mach(4)) */
    }
#else
/* For IEEE double precision DBL_EPSILON = 2^-52 = 2.220446049250313e-16 :
 * (xmin, xmax) are non-trivial, see ./gammalims.c
 * xsml = exp(.01)*DBL_MIN
 * dxrel = sqrt(DBL_EPSILON) = 2 ^ -26
*/
# define ngam 22
# define xmin -170.5674972726612
# define xmax  171.61447887182298
# define xsml 2.2474362225598545e-308
# define dxrel 1.490116119384765696e-8
#endif

现在我知道这段代码正在初始化ngam，xsml，dxrel等变量的值。但我不明白什么是NOMORE_FOR_THREADS。

我无法找到定义的位置，因此我很困惑何时会输入#ifdef子句，或者只是进入#else子句并根据IEEE标准定义变量。 / p>

如果有人能够了解NOMORE_FOR_THREADS或其定义的内容，那将非常有用。

感谢您的帮助。

Answer 1

看起来在修订版13433中添加了<div id="demo" class="collapse in width" style="background-color:yellow;float:right;">：

#ifdef

这是与之前版本的差异：

> svn log -vr13433
------------------------------------------------------------------------
r13433 | maechler | 2001-04-10 10:05:54 -0500 (Tue, 10 Apr 2001) | 2 lines
Changed paths:
   M /trunk/src/nmath/beta.c
   M /trunk/src/nmath/gamma.c
   M /trunk/src/nmath/lgamma.c
   M /trunk/src/nmath/lgammacor.c

globals now #ifdef NOMORE_FOR_THREADS

------------------------------------------------------------------------

我没有在该版本的源代码中的任何位置定义> svn diff -r13432:13433 src/nmath/gamma.c Index: src/nmath/gamma.c =================================================================== --- src/nmath/gamma.c (revision 13432) +++ src/nmath/gamma.c (revision 13433) @@ -1,7 +1,7 @@ /* * Mathlib : A C Library of Special Functions * Copyright (C) 1998 Ross Ihaka - * Copyright (C) 2000 The R Development Core Team + * Copyright (C) 2000-2001 The R Development Core Team * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by @@ -40,7 +40,7 @@ double gammafn(double x) { - static /* const */ double gamcs[42] = { + const double gamcs[42] = { +.8571195590989331421920062399942e-2, +.4415381324841006757191315771652e-2, +.5685043681599363378632664588789e-1, @@ -89,6 +89,7 @@ double y; double sinpiy, value; +#ifdef NOMORE_FOR_THREADS static int ngam = 0; static double xmin = 0, xmax = 0., xsml = 0., dxrel = 0.; @@ -101,6 +102,18 @@ /* = exp(.01)*DBL_MIN = 2.247e-308 for IEEE */ dxrel = sqrt(1/DBL_EPSILON);/*was (1/d1mach(4)) */ } +#else +/* For IEEE double precision DBL_EPSILON = 2^-52 = 2.220446049250313e-16 : + * (xmin, xmax) are non-trivial, see ./gammalims.c + * xsml = exp(.01)*DBL_MIN + * dxrel = sqrt(1/DBL_EPSILON) = 2 ^ 26 +*/ +# define ngam 22 +# define xmin -170.5674972726612 +# define xmax 171.61447887182298 +# define xsml 2.2474362225598545e-308 +# define dxrel 67108864. +#endif if(ISNAN(x)) return x;，在添加它之后的下几百个修订版本或当前版本中。它可能（虽然似乎不太可能）可以在某些系统头文件中定义。它似乎更有可能通过命令行参数指定。

R语言源代码 - C代码中的`NOMORE_FOR_THREADS`是什么

1 个答案: