language semantics shouldn't depend on the compiler

[andychu]

Perl even documents this:

https://perldoc.perl.org/perlnumber.html#Storing-numbers

Perl can internally represent numbers in 3 different ways: as native integers, as native floating point numbers, and as decimal strings. Decimal strings may have an exponential notation part, as in "12.34e-56" . Native here means "a format supported by the C compiler which was used to build perl".

I think integer and floating point semantics are reasonably well defined though?

Issues:

• Oil uses 32 bit int (even on 64 bit) while other shells use 64 bits (long int)
• printf had an issue, with negative numbers I think

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In theory we want Oil on two different machines to behave the same way, even if they were compiled with a different compiler. It makes things more reproducible

[andychu]

Integer overflow is undefined behavior in C.

When undefined behavior is invoked, the behavior depends on the compiler. So we should avoid overflow for user operations.

Instead we can use these compiler extensions:

https://gcc.gnu.org/onlinedocs/gcc/Integer-Overflow-Builtins.html

https://clang.llvm.org/docs/LanguageExtensions.html

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Also TODO:

• document portability
  • we use the EXTGLOB extension for GNU glob
  • and eventually these overflow builtins
  • otherwise it's ISO C++11 and POSIX