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From: maine@altair.dfrf.nasa.gov (Richard Maine)
Newsgroups: comp.lang.fortran
Subject: Re: Uses for EQUIVALENCE
Message-ID: <MAINE.91Jun7111515@altair.dfrf.nasa.gov>
Date: 7 Jun 91 18:15:15 GMT
References: <1991Jun1.171914.802@weyrich.UUCP>
	<1991Jun5.220805.4653@alchemy.chem.utoronto.ca>
	<1991Jun6.232026.10172@jato.jpl.nasa.gov>
	<1991Jun7.171357.3941@eplrx7.uucp>
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In-reply-to: leipold@eplrx7.uucp's message of 7 Jun 91 17:13:57 GMT

On 7 Jun 91 17:13:57 GMT, leipold@eplrx7.uucp (Walt Leipold) said:

Walt> EPS(), HUGE()) for each constant?  And why aren't functions like
Walt> this part of X3.9-1978, so I can write portable numerical code?
Walt> Or (the real $64K question) are these functions included in the
Walt> long-expected and oft-delayed FORTRAN 90?

Yes.  From the S8.115 (June 1990) draft of F90,  (More detailed
descriptions are in other subsections; also pardon any typos I might
have made in transcribing this).

  13.10.8 Numeric Inquiry Functions

    digits(x)      - Number of significant digits in the model
    epsilon(x)     - Number that is almost negligible compared to one
    huge(x)        - Largest number in the model
    maxexponent(x) - Maximum exponent in the model
    minexponent(x) - Minimum exponent in the model
    precision(x)   - decimal precision
    radix(x)       - base of model
    range(x)       - decimal exponent range
    tiny(x)        - Smallest positive number in the model

  13.10.9 Bit Inquiry Function

    bit_size(i)    - Number of bits in the model

  13.10.10 Bit Manipulation Functions

    ...

  13.10.12 Floating-point Manipulation Functions

    exponent(x)       - Exponent part of a modewl number
    fraction(x)       - Fractional part of a model number
    nearest(x,s)      - Nearest different processor number in given direction
    rrspacing(x)      - Reciprocal of the relative spacing
                          of model numbers near given number
    scale(x,i)        - Multiply a real by its base to an integer power
    set_exponent(x,i) - Set exponent part of a number
    spacing(x)        - Absolute spacing of model numbers near given
                          number

Also relevant are the selected_int_kind and selected_real_kind
functions that allow you to portably specify what precision you want
as in

        !--- You probably put the parameter declaration in a module
        !--- or include file when doing thid for real.
        integer, parameter :: wr_kind = selected_real_kind(10,30)

        real(wr_kind) :: x,y,z

That specifies that x, y, and z are of the "smallest" floating point
type that has at least 10 digits of precision and a range
of at least 10**(-30) to 10**30.  This would be double precision on
most 32-bit systems and single precision on 60- and 64-bit ones.


--
--
Richard Maine
maine@altair.dfrf.nasa.gov