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Date: Tue, 6 Sep 2022 14:21:52 +0200
From: Gabriel Ravier <>
To:, Joakim Sindholt <>
Subject: Re: ecvt(0, 0, ...) is broken

On 9/6/22 14:13, Joakim Sindholt wrote:
> On Tue, 6 Sep 2022 12:12:48 +0200, Gabriel Ravier <> wrote:
>> Executing ecvt(0, 0, &decpt, &sign) results in musl returning
>> "000000000000000".
>> This seems highly likely to be a bug considering that glibc returns ""
>> and I see no plausible reasoning for musl's behavior that could be
>> justified by the standard.
> POSIX.1-2001 said:
>> The ecvt() function shall convert value to a null-terminated string of
>> ndigit digits (where ndigit is reduced to an unspecified limit
>> determined by the precision of a double) and return a pointer to the
>> string. The high-order digit shall be non-zero, unless the value is 0.
> The first part would imply that ndigit=0 should return the string "" but
> the second part makes no provision for a zero-digit-long string.
> I would say ndigit=0 is UB.
Wouldn't that then mean that any request call of fcvt with a small 
ndigits but very small value that isn't 0, as in my previous email, 
would also be UB (since if my logic is correct, the string cannot start 
with a 0 but it also cannot start with any other value, which forces it 
to be empty) ? That seems rather excessive...

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