Re: [Qemu-devel] [PATCH v2 1/9] cutils: Add qemu_strtod() and qemu_strtod_finite()

[David Hildenbrand <david@redhat.com>]

On 20.11.18 21:07, Markus Armbruster wrote:
> Eric Blake <eblake@redhat.com> writes:
> 
>> On 11/20/18 3:25 AM, David Hildenbrand wrote:
>>> Let's provide a wrapper for strtod().
>>>
>>> Reviewed-by: Eric Blake <eblake@redhat.com>
>>
>> This changed enough from v1 that I would have dropped R-b to ensure
>> that reviewers notice the differences.

Indeed, dropping it now ;)

>>
>>> Signed-off-by: David Hildenbrand <david@redhat.com>
>>> ---
>>>   include/qemu/cutils.h |  2 ++
>>>   util/cutils.c         | 65 +++++++++++++++++++++++++++++++++++++++++++
>>>   2 files changed, 67 insertions(+)
>>>
>>
>>> + * If the conversion overflows, store +/-HUGE_VAL in @result, depending
>>> + * on the sign, and return -ERANGE.
>>> + *
>>> + * If the conversion underflows, store ±0.0 in @result, depending on the
>>> + * sign, and return -ERANGE.
>>
>> The use of UTF-8 ± in one place but not both is odd.  I think we're at
>> the point where UTF-8 comments are acceptable these days, rather than
>> trying to keep our codebase ASCII-clean, so I don't care which way you
>> resolve the inconsistency.
> 
> 217 out of 6455 git-controlled files contain non-ASCII characters.  53
> of them are binary, and don't count.  In most text files, it's for
> spelling names of authors properly in comments.  Ample precedence for
> UTF-8 in comments, I'd say.
> 
> That said, I second Eric's call for consistency, with the slightest of
> preferrences for plain ASCII.

I'll just go with +/-. Thanks.

> 
> I spotted UTF-8 in two error messages, which might still be unadvisable:
> 
> hw/misc/tmp105.c:        error_setg(errp, "value %" PRId64 ".%03" PRIu64 " °C is out of range",
> hw/misc/tmp421.c:        error_setg(errp, "value %" PRId64 ".%03" PRIu64 " °C is out of range",
> 
>>> +/**
>>> + * Convert string @nptr to a finite double.
>>> + *
>>> + * Works like qemu_strtod(), except that "NaN" and "inf" are rejected
>>> + * with -EINVAL and no conversion is performed.
>>> + */
>>> +int qemu_strtod_finite(const char *nptr, const char **endptr, double *result)
>>> +{
>>> +    double tmp;
>>> +    int ret;
>>> +
>>> +    ret = qemu_strtod(nptr, endptr, &tmp);
>>> +    if (ret) {
>>> +        return ret;
>>
>> So, if we overflow, we are returning -ERANGE but with nothing stored
>> into *result.  This is different from qemu_strtod(), where a return of
>> -ERANGE guarantees that *result is one of 4 values (+/- 0.0/inf).
>> That seems awkward.
> 
> Violates the contract's "like qemu_strtod()".

Right, I missed that. What about something like this:

int qemu_strtod_finite(const char *nptr, const char **endptr, double
*result)
{
    double tmp;
    int ret;

    ret = qemu_strtod(nptr, endptr, &tmp);
    if (!ret && !isfinite(tmp)) {
        if (endptr) {
            *endptr = nptr;
        }
        ret = -EINVAL;
    }

    if (ret != -EINVAL) {
        *result = tmp;
    }
    return ret;
}



-- 

Thanks,

David / dhildenb