Markus Armbruster <arm...@redhat.com> wrote: > From: Fangrui Song <i...@maskray.me> > > Clang does not like do_strtosz()'s code to guard against overflow: > > qemu/util/cutils.c:245:23: error: implicit conversion from 'unsigned > long' to 'double' changes value from 18446744073709550592 to > 18446744073709551616 [-Werror,-Wimplicit-int-float-conversion] > > The warning will be enabled by default in clang 10. It is not > available for clang <= 9. > > val * mul >= 0xfffffffffffffc00 is indeed wrong. 0xfffffffffffffc00 > is not representable exactly as double. It's half-way between the > representable values 0xfffffffffffff800 and 0x10000000000000000. > Which one we get is implementation-defined. Bad. > > We want val * mul > (the largest uint64_t exactly representable as > double). That's 0xfffffffffffff800. Write it as nextafter(0x1p64, 0) > with a suitable comment. > > Signed-off-by: Fangrui Song <i...@maskray.me> > Reviewed-by: Markus Armbruster <arm...@redhat.com> > [Patch split, commit message improved] > Signed-off-by: Markus Armbruster <arm...@redhat.com>
Reviewed-by: Juan Quintela <quint...@redhat.com> Learning this *new* C99 float format O:-)
