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| /qemu/util/ |
| H A D | cutils.c | diff 25f74087 Fri Nov 22 08:00:39 GMT 2019 Fangrui Song <i@maskray.me> util/cutils: Fix incorrect integer->float conversion caught by clang
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 <armbru@redhat.com>
[Patch split, commit message improved]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20191122080039.12771-3-armbru@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Juan Quintela <quintela@redhat.com>
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