Re: [PATCH v2 19/19] cutils: Improve qemu_strtosz handling of fractions

[Hanna Czenczek <hreitz@redhat.com>]

On 12.05.23 04:10, Eric Blake wrote:
> We have several limitations and bugs worth fixing; they are
> inter-related enough that it is not worth splitting this patch into
> smaller pieces:
>
> * ".5k" should work to specify 512, just as "0.5k" does
> * "1.9999k" and "1." + "9"*50 + "k" should both produce the same
>    result of 2048 after rounding
> * "1." + "0"*350 + "1B" should not be treated the same as "1.0B";
>    underflow in the fraction should not be lost
> * "7.99e99" and "7.99e999" look similar, but our code was doing a
>    read-out-of-bounds on the latter because it was not expecting ERANGE
>    due to overflow. While we document that scientific notation is not
>    supported, and the previous patch actually fixed
>    qemu_strtod_finite() to no longer return ERANGE overflows, it is
>    easier to pre-filter than to try and determine after the fact if
>    strtod() consumed more than we wanted.  Note that this is a
>    low-level semantic change (when endptr is not NULL, we can now
>    successfully parse with a scale of 'E' and then report trailing
>    junk, instead of failing outright with EINVAL); but an earlier
>    commit already argued that this is not a high-level semantic change
>    since the only caller passing in a non-NULL endptr also checks that
>    the tail is whitespace-only.
>
> Fixes: https://gitlab.com/qemu-project/qemu/-/issues/1629
> Fixes: cf923b78 ("utils: Improve qemu_strtosz() to have 64 bits of precision", 6.0.0)
> Fixes: 7625a1ed ("utils: Use fixed-point arithmetic in qemu_strtosz", 6.0.0)
> Signed-off-by: Eric Blake <eblake@redhat.com>
>
> ---
>
> v2: more changes, handle negatives differently, catch fractions that
> round to 0 but don't underflow [Hanna]
> ---
>   tests/unit/test-cutils.c | 50 +++++++++-------------
>   util/cutils.c            | 89 ++++++++++++++++++++++++++++++----------
>   2 files changed, 86 insertions(+), 53 deletions(-)

Reviewed-by: Hanna Czenczek <hreitz@redhat.com>