Re: Non-decimal integer literals

On Wed, Nov 23, 2022 at 3:54 PM David Rowley <dgrowleyml(at)gmail(dot)com> wrote:
>
> Going by [1], clang will actually use multiplication by 16 to
> implement the former. gcc is better and shifts left by 4, so likely
> won't improve things for gcc. It seems worth doing it this way for
> anything that does not have HAVE__BUILTIN_OP_OVERFLOW anyway.

FWIW, gcc 12.2 generates an imul on my system when compiling in situ. I've
found it useful to run godbolt locally* and load the entire PG file (nicer
to read than plain objdump) -- compilers can make different decisions when
going from isolated snippets to within full functions.

* clone from https://github.com/compiler-explorer/compiler-explorer
install npm 16
run "make" and when finished will show the localhost url
add the right flags, which in this case was

-Wall -Wmissing-prototypes -Wpointer-arith -Wdeclaration-after-statement
-Werror=vla -Wendif-labels -Wmissing-format-attribute
-Wimplicit-fallthrough=3 -Wcast-function-type -Wformat-security
-fno-strict-aliasing -fwrapv -fexcess-precision=standard
-Wno-format-truncation -Wno-stringop-truncation -O2
-I/path/to/srcdir/src/include -I/path/to/builddir/src/include -D_GNU_SOURCE

--
John Naylor
EDB: http://www.enterprisedb.com