GNU Extension and intrinsics

[Mark Eggleston <mark dot eggleston at codethink dot co dot uk>]

A number of intrinsic functions have two parameters that must match by 
type and kind such as "dim" and "mod". In addition there are two 
intrinsics "max" and "min" that also require the parameters to match by 
type and kind. The documentation for "max" and "min" at 
https://gcc.gnu.org/onlinedocs/gfortran/Intrinsic-Procedures.html#Intrinsic-Procedures 
states for the parameters following the first that "As a GNU extension, 
arguments of different kinds are permitted."

Using -std=f95 the following error is produced:

25 |   write(*,*) max(1_1, 2_4, 6_4)
   |                      1
Error: GNU Extension: Different type kinds at (1)


The same error is also produced for "dim", "mod" and "modulo" but not "sign"
e.g.:

26 |   write(*,*) modulo(17, 5_2)
   |                        1
Error: GNU Extension: Different type kinds at (1)

There is no mention of the GNU extension applying to "dim", "mod" and 
"modulo". The intrinsic "sign" has its parameter described in the same 
way as mod so should the GNU Extension also apply to sign?

According to the standard (N692 Fortran 90) the type and kind of the 
return parameter should match that of the first parameter. The GNU 
Extension is not standard, for dim, mod and modulo the kind of the 
return type is the higher of the two parameters so the return type for 
mod(33_2, 5_4) is integer(4) instead of integer(2).

Comparing with PGI Fortran: its the return type for mod(33_2, 5_4) is 
integer(2). Oddly PGI Fortran returns integer(4) for mod(67_1, 4_1). PGI 
Fortran also accepts different types: mod(67_2, 4.0) will
return an integer(2).

Should the GNU Extension apply to sign?

The documentation should be updated to reflect where the GNU Extension 
applies.

Should the return type always match the type of the first parameter?

Would it be reasonable to modify the GNU Extension to allow for 
different types (integer or real) as well as different kinds?

Mark

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