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

[Luc Michel]

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. 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++;
    }

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

is enough?

-- 
Luc

> +}
> +
>  int qemu_pstrcmp0(const char **str1, const char **str2)
>  {
>      return g_strcmp0(*str1, *str2);
> -- 
> 2.26.2
>