Re: [bug-gawk] inside awk script check that -M/--bignum given on command line?

[arnold]

There is also PROCINFO["argv"] in 4.2.0, which lets you
see the command line arguments passed to gawk.

HTH,

Arnold

"Andrew J. Schorr" <address@hidden> wrote:

> Hi,
>
> On Thu, Jan 04, 2018 at 11:57:05PM +0100, Jannick wrote:
> > I am running gawk (4.2.0) against an awk script requiring that the --bignum
> > mode (-M) is effectively switched on. Otherwise no meaningful, but rather
> > confusing results are produced.
> > 
> > Is there any way (1) to run a check inside the script that the -M/--bignum
> > flag was provided on the command line (if negative exit my script) or (2) to
> > switch on/off the bignum mode inside the script (like IGNORECASE=1 or =0; I
> > wouldn't mind if it could be switched on only)? 
> > 
> > To make sure that the MPR lib is compiled into gawk can be checked iff
> > PROCINFO["mpfr_version"] is given. However the default values of PREC (=5)
> > and ROUNDMODE(="N") do not appear to provide any insight if -M was given I
> > think. 
>
> This issue has arisen in the past. There is a section in the documentation
> about this:
>
> https://www.gnu.org/software/gawk/manual/html_node/Checking-for-MPFR.html
>
> Occasionally, you might like to be able to check if 'gawk' was invoked
> with the '-M' option, enabling arbitrary-precision arithmetic.  You can
> do so with the following function, contributed by Andrew Schorr:
>
>      # adequate_math_precision --- return true if we have enough bits
>
>      function adequate_math_precision(n)
>      {
>          return (1 != (1+(1/(2^(n-1)))))
>      }
>
>    Here is code that invokes the function in order to check if
> arbitrary-precision arithmetic is available:
>
>      BEGIN {
>          # How many bits of mantissa precision are required
>          # for this program to function properly?
>          fpbits = 123
>
>          # We hope that we were invoked with MPFR enabled. If so, the
>          # following statement should configure calculations to our desired
>          # precision.
>          PREC = fpbits
>
>          if (! adequate_math_precision(fpbits)) {
>              print("Error: insufficient computation precision available.\n" \
>                    "Try again with the -M argument?") > "/dev/stderr"
>              exit 1
>          }
>      }
>
> Does this solve your problem?
>
> Regards,
> Andy