Question

我正在使用Windows Vista 64位。

我需要编译一个Fortran文件，我需要编辑该文件以匹配我的机器的“机器相关常量”

在该文件中，我有以下信息。任何建议都会有很大帮助。感谢

C Explanation of machine-dependent constants
C
C   XINF   = largest positive machine number
C   XMAX1  = beta ** (p-1), where beta is the radix for the
C            floating-point system, and p is the number of base-beta
C            digits in the floating-point significand.  This is an
C            upper bound on non-integral floating-point numbers, and
C            the negative of the lower bound on acceptable negative
C            arguments for PSI.  If rounding is necessary, round this
C            value down.
C   XMIN1  = the smallest in magnitude acceptable argument.  We
C            recommend XMIN1 = MAX(1/XINF,xmin) rounded up, where
C            xmin is the smallest positive floating-point number.
C   XSMALL = absolute argument below which  PI*COTAN(PI*X)  may be
C            represented by 1/X.  We recommend XSMALL < sqrt(3 eps)/pi,
C            where eps is the smallest positive number such that
C            1+eps > 1. 
C   XLARGE = argument beyond which PSI(X) may be represented by
C            LOG(X).  The solution to the equation
C               x*ln(x) = beta ** p
C            is a safe value.
C
C     Approximate values for some important machines are
C
C                        beta  p     eps     xmin       XINF  
C
C  CDC 7600      (S.P.)    2  48  7.11E-15  3.13E-294  1.26E+322
C  CRAY-1        (S.P.)    2  48  7.11E-15  4.58E-2467 5.45E+2465
C  IEEE (IBM/XT,
C    SUN, etc.)  (S.P.)    2  24  1.19E-07  1.18E-38   3.40E+38
C  IEEE (IBM/XT,
C    SUN, etc.)  (D.P.)    2  53  1.11D-16  2.23E-308  1.79D+308
C  IBM 3033      (D.P.)   16  14  1.11D-16  5.40D-79   7.23D+75
C  SUN 3/160     (D.P.)    2  53  1.11D-16  2.23D-308  1.79D+308
C  VAX 11/780    (S.P.)    2  24  5.96E-08  2.94E-39   1.70E+38
C                (D.P.)    2  56  1.39D-17  2.94D-39   1.70D+38
C   (G Format)   (D.P.)    2  53  1.11D-16  5.57D-309  8.98D+307
C
C                         XMIN1      XMAX1     XSMALL    XLARGE
C
C  CDC 7600      (S.P.)  3.13E-294  1.40E+14  4.64E-08  9.42E+12
C  CRAY-1        (S.P.)  1.84E-2466 1.40E+14  4.64E-08  9.42E+12
C  IEEE (IBM/XT,
C    SUN, etc.)  (S.P.)  1.18E-38   8.38E+06  1.90E-04  1.20E+06
C  IEEE (IBM/XT,
C    SUN, etc.)  (D.P.)  2.23D-308  4.50D+15  5.80D-09  2.71D+14
C  IBM 3033      (D.P.)  1.39D-76   4.50D+15  5.80D-09  2.05D+15
C  SUN 3/160     (D.P.)  2.23D-308  4.50D+15  5.80D-09  2.71D+14
C  VAX 11/780    (S.P.)  5.89E-39   8.38E+06  1.35E-04  1.20E+06
C                (D.P.)  5.89D-39   3.60D+16  2.05D-09  2.05D+15
C   (G Format)   (D.P.)  1.12D-308  4.50D+15  5.80D-09  2.71D+14
C

Answer 1

你在睡觉前就抓住了我，所以我会把它缩短（因为我不能在这种情况下写出明智的答案）。 Fortran引入了许多用于确定系统相关常量的函数 - 拿一本书或一个互联网教程，查找SELECTED_REAL_KIND，EPSILON（以及那里经常出现的链接）等函数。

Answer 2

现代英特尔CPU使用IEEE兼容的浮点运算 - 似乎所有这些机器常数都与浮点值有关，而不是整数。因此，我认为您应该很好地复制您所显示的表中IEEE行的值。 S.P.和D.P引用单精度和双精度，您可能需要在其他地方指定它并在表格中选择相应的行。

如何知道机器相关的常数

2 个答案: