[PATCH xserver] squash! sync: Convert from "CARD64" to int64_t.

Keith Packard keithp at keithp.com
Thu Aug 24 23:27:03 UTC 2017

Eric Anholt <eric at anholt.net> writes:

> ---
> We pass the overflow unit tests both before and after this change, but
> this should be safer.

I've seen GCC do precisely the 'optimization' you are concerned about,
but only when one of the operands is constant. One should use -fwrapv
whenever using gcc so that you get correct behavior, instead of
compiler-writers-potluck. I hope the gcc authors agree with your reading
of the spec in this case; it's getting very hard to trust them to ever
do the right thing though.

Reviewed-by: Keith Packard <keithp at keithp.com>

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