Re: gawk -M using int() changes results

[arnold]

Hi.

Thanks for the report. It's not really a bug. Instead, you need to
increase the precision of the floating point values used. I found
that setting PREC = 65 caused your example to work, but you may need
more precision as your numbers get bigger.

$ cat intbug.awk 
  BEGIN {
   PREC = 65
   N = 123456789101112131415;
   print int( N / 10 );
   print ( N - N % 10 ) / 10;
  }
$ ./gawk -M -f intbug.awk
12345678910111213141
12345678910111213141

Thanks,

Arnold


João Oliveira <joao.souza@pucrs.br> wrote:

> Configuration Information [Automatically generated, do not change]:
> Machine: x86_64
> OS: linux-gnu
> Compiler: gcc
> Compilation CFLAGS: -g -O2 -DNDEBUG
> uname output: Linux caliope 5.15.0-116-generic #126~20.04.1-Ubuntu SMP Mon 
> Jul 1 15:40:07 UTC 2024 x86_64 x86_64 x86_64 GNU/Linux
> Machine Type: x86_64-pc-linux-gnu
>
> Gawk Version: 5.3.0
>
> Attestation 1:
>       I have read 
> https://www.gnu.org/software/gawk/manual/html_node/Bugs.html.
>       Yes
>
> Attestation 2:
>       I have not modified the sources before building gawk.
>       True
>
> Description:
>       When gawk -M is used, int() seems to be unable to cope properly with
>  numbers that are "too big", possibly bigger than a 64-bit integer. 
>
>  I was using large numbers and wanted to do something like
>
>     n = int( n / 10 ) // remove last decimal digit
>
>  and at a certain size results started to be wrong. On the other hand,
>  doing 
>
>     n = ( n - n % 10 ) / 10 // remove last decimal digit
>
>  works properly.
>  I was unable to find whether this is a known and accepted effect or a
>  real bug, so I decided to report it anyway.
>
> Repeat-By:
>
>   run gawk -M with
>
>   BEGIN {
>    N = 123456789101112131415;
>    print int( N / 10 );
>    print ( N - N % 10 ) / 10;
>   }
>