[Libguestfs] [PATCH nbdinfo v2 1/3] common/utils: Add function to convert sizes to human-readable

[Laszlo Ersek]

On 09/20/21 18:39, Richard W.M. Jones wrote:
> On Mon, Sep 20, 2021 at 06:25:34PM +0200, Laszlo Ersek wrote:
>> On 09/20/21 13:04, Richard W.M. Jones wrote:

>>> +/* If you allocate a buffer of at least this length in bytes and pass
>>> + * it as the first parameter to human_size, then it will not overrun.
>>> + */
>>> +#define HUMAN_SIZE_LONGEST 64
>>
>> (5) The integer constant expression
>>
>>   ((sizeof (uint64_t) * 8 + 2) / 3 + 1)
>>
>> would be more frugal (but we might not care).
>>
>> If we take the number of three-bit groups in the word, and divide that
>> by three -- rounded up --, we get the number of necessary octal digits.
>> The number of decimal digits needed never exceeds the number of octal
>> digits needed, so this is safe. Add one character for the NUL terminator.)
> 
> Yeah I was just guessing here.  FWIW gnulib really does the hard work:
> 
> https://git.savannah.gnu.org/gitweb/?p=gnulib.git;a=blob;f=lib/human.h;h=61f110fc0215205039ec9729ab34e68686c2d102;hb=HEAD#l30

I was prepared to mention log10(2) and that we could approximate it more
closely than with 1/3; gnulib didn't disappoint this time either! :)

Thanks!
Laszlo