Re: [PATCH 1/3] util/cutils: Introduce freq_to_str() to display Hertz units

[Philippe Mathieu-Daudé]

On 9/28/20 9:50 AM, Luc Michel wrote:
> Hi Philippe,
> 
> On 11:08 Sun 27 Sep     , Philippe Mathieu-Daudé wrote:
>> Introduce freq_to_str() to convert frequency values in human
>> friendly units using the SI units for Hertz.
>>
>> Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
>> ---
>>  include/qemu/cutils.h | 12 ++++++++++++
>>  util/cutils.c         | 10 ++++++++++
>>  2 files changed, 22 insertions(+)
>>
>> diff --git a/include/qemu/cutils.h b/include/qemu/cutils.h
>> index eb59852dfdf..0186c846e9c 100644
>> --- a/include/qemu/cutils.h
>> +++ b/include/qemu/cutils.h
>> @@ -158,6 +158,18 @@ int qemu_strtosz_metric(const char *nptr, const char 
>> **end, uint64_t *result);
>>  
>>  char *size_to_str(uint64_t val);
>>  
>> +/**
>> + * freq_to_str:
>> + * @freq_hz: frequency to stringify
>> + *
>> + * Return human readable string for frequency @freq_hz.
>> + * Use SI units like KHz, MHz, and so forth.
>> + *
>> + * The caller is responsible for releasing the value returned with g_free()
>> + * after use.
>> + */
>> +char *freq_to_str(uint64_t freq_hz);
>> +
>>  /* used to print char* safely */
>>  #define STR_OR_NULL(str) ((str) ? (str) : "null")
>>  
>> diff --git a/util/cutils.c b/util/cutils.c
>> index 36ce712271f..dab837fd8b8 100644
>> --- a/util/cutils.c
>> +++ b/util/cutils.c
>> @@ -885,6 +885,16 @@ char *size_to_str(uint64_t val)
>>      return g_strdup_printf("%0.3g %sB", (double)val / div, suffixes[i]);
>>  }
>>  
>> +char *freq_to_str(uint64_t freq_hz)
>> +{
>> +    static const char *suffixes[] = { "", "K", "M", "G", "T", "P", "E" };
>> +    unsigned unit_index = log10(freq_hz) / 3;
>> +
>> +    return g_strdup_printf("%0.3g %sHz",
>> +                           freq_hz / pow(10.0, unit_index * 3.0),
>> +                           suffixes[unit_index]);
> 
> You could end up going out of your 'suffixes' array if freq_hz is very
> high.

Oh, good point.

> Also, to avoid the complexity of log10/pow, maybe something like:
> 
>     double freq = freq_hz;
>     size_t idx = 0;
> 
>     while (freq >= 1000.0 && idx < ARRAY_LENGTH(suffixes)) {
>         freq /= 1000.0;
>         idx++;
>     }

KISS, I like it :)

> 
>     return g_strdup_printf("%0.3g %sHz", freq, suffixes[idx]);
> 
> is enough?
> 

I'll respin, thanks!

Phil.