Longreal gives the correct result:
 

samiam@samiam-home-pc:~/projects/pascal/pascal-p5$ cat test.pas
program test(output);

var b,c: longreal;

begin

b := maxint;
c := 10.0;
b := b+c;
writeln(b:40:1);

writeln(maxint:38);

end.
samiam@samiam-home-pc:~/projects/pascal/pascal-p5$ gpc -o test test.pas
samiam@samiam-home-pc:~/projects/pascal/pascal-p5$ ./test
9223372036854775817.0
9223372036854775807

--------- Original Message ---------
Subject: Errrr what?
From: "scott andrew franco" <samiam@moorecad.com>
Date: 8/31/20 1:07 pm
To: "gpc@gnu.de" <gpc@gnu.de>

samiam@samiam-home-pc:~/projects/pascal/pascal-p5$ cat test.pas
program test(output);

var b,c: real;

begin

b := maxint;
c := 10.0;
b := b+c;
writeln(b:40:1);

writeln(maxint:38);

end.
samiam@samiam-home-pc:~/projects/pascal/pascal-p5$ gpc -o test test.pas
samiam@samiam-home-pc:~/projects/pascal/pascal-p5$ ./test
9223372036854775808.0
9223372036854775807