Fl crashes on -9223372036854775808LL but accepts 2LL^63

[Eric Hivon]

Some IDL codes, for instance https://github.com/wlandsman/IDLAstro/blob/master/pro/mrdfits.pro (line 982)
use the literal value -9223372036854775808LL, which is accepted in IDL, but makes FL crash with the error
\% Error: number too big: 9223372036854775808
while FL would accept 2LL^63 which has the same numerical value.

[Lajos Foldy]

I think the bug is in IDL. “-9223372036854775808LL” is parsed (both in IDL and FL) as two tokens, a unary minus and a signed integer. 9223372036854775808LL is too big for a 64 bit signed integer, the valid range is from −9,223,372,036,854,775,808 to 9,223,372,036,854,775,807.

Try this:

IDL> var=9223372036854775808LL
IDL> help, var
VAR LONG64 = -9223372036854775808

IDL silently assigns a big negative value to var, instead of the big positive value. In FL, you get an error:

If I compile FL with a sanitizer, I get a warning for 2LL^63, too (signed overflow, and that is undefined in C/C++).

Here is a minimal Fortran example:

integer(kind=8) x
x=2
write (*,*) x**63
stop
end

Compiling this with gfortran -fsanitize=undefined a.f I get a runtime error:

a.f:3:23: runtime error: signed integer overflow: 134217728 * 68719476736 cannot be represented in type 'integer(kind=8)'

x=-9223372036854775808gives a compile time error:

2 |       x=-9223372036854775808
|                             1
Error: Integer too big for its kind at (1). This check can be disabled with the option ‘-fno-range-check’

So, if it is an error in Fortran, it should be an error in IDL, too.

The proper way to assign -9223372036854775808 to a 64 bit signed integer is: var='8000000000000000'xll

Or var=-9223372036854775807ll-1ll

[Lajos Foldy]

The 32 bit version gives an error even in IDL, so the missing error for the 64 bit integer is really an IDL bug:

IDL> help, -2147483648l

help, -2147483648
       ^
% Long integer constant must be less than 2147483648.

The 64 bit version gives a different result in GDL:

GDL> help, -9223372036854775808ll
<Expression>    LONG64    =                      1

‌

-9223372036854775807-1 works everywhere.

[Lajos Foldy]

I have made an exception for 9223372036854775808, the error is replaced with a warning.

[Lajos Foldy]

Closed.