Re: printf "%010a" Inf/NaN and FreeBSD

[Eric Blake]

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According to Bruno Haible on 4/5/2007 5:14 AM:
> Eric Blake wrote:
>>> I find glibc's output more sensible, since strtod will accept it, while
>>> strtod will not grok "0000000inf". But FreeBSD appears to be closer to
>>> the POSIX wording, I won't count it as a FreeBSD bug.
>> I would, though.  POSIX allows "inf" vs. "infinity", but unless %010f
>> prints "0000000inf", I don't think %010a should do so either, because
>> POSIX was clear that "A double argument representing an infinity or NaN
>> shall be converted in the style of an f or F conversion specifier."
> 
> There is also the description of the '0' flag, which says the same for 'a'
> as for 'f':
>    "For d , i , o , u , x , X , a , A , e , E , f , F , g , and G conversion
>     specifiers, leading zeros (following any indication of sign or base) are
>     used to pad to the field width; no space padding is performed."

Yes, I read that too.  And with %a, "0000000nan" has no indication of
base, so it violates the above statement (the leading zeros must follow
the 0x, but with nan, there is no 0x).  Your argument about strtod being
able to parse printf results is also an important factor, because real
code expects that to work.  That's now three reasons why I think FreeBSD's
behavior is wrong.

> 
> POSIX doesn't guarantee it. And on systems where the number of mantissa bits
> (including the hidden bit) is not congruent to 1 modulo 4, the printf
> implementor might choose to map the bits in a predefined way,

Fair enough.  I won't make you do it if platforms don't do it; it was only
a quality-of-implementation suggestion.

- --
Don't work too hard, make some time for fun as well!

Eric Blake             address@hidden
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