Peter Xu <pet...@redhat.com> writes:
> I stole the algorithm from print_type_size(). I didn't generalize it
> since that's using [KM...]iB while here we need [KM...]B to finally
> be able to stands for page sizes (and even more general).
Can you explain why we need units without the 'i' here?
>
> Signed-off-by: Peter Xu <pet...@redhat.com>
> ---
> include/qemu-common.h | 1 +
> util/cutils.c | 26 ++++++++++++++++++++++++++
> 2 files changed, 27 insertions(+)
>
> diff --git a/include/qemu-common.h b/include/qemu-common.h
> index d218821..d7d0448 100644
> --- a/include/qemu-common.h
> +++ b/include/qemu-common.h
> @@ -145,6 +145,7 @@ void qemu_hexdump(const char *buf, FILE *fp, const char
> *prefix, size_t size);
> int parse_debug_env(const char *name, int max, int initial);
>
> const char *qemu_ether_ntoa(const MACAddr *mac);
> +char *size_to_str(double val);
> void page_size_init(void);
>
> /* returns non-zero if dump is in progress, otherwise zero is
> diff --git a/util/cutils.c b/util/cutils.c
> index 50ad179..5aaf370 100644
> --- a/util/cutils.c
> +++ b/util/cutils.c
> @@ -619,3 +619,29 @@ const char *qemu_ether_ntoa(const MACAddr *mac)
>
> return ret;
> }
> +
> +/*
> + * Sample output:
> + *
> + * 1 -> "1 B"
> + * 528 -> "0.516 KB"
> + * 4096 -> "4 KB"
> + * 2402958 -> "2.29 MB"
> + * 1073741824 -> "1 GB"
> + *
> + * Please free the buffer after use.
> + */
> +char *size_to_str(double val)
> +{
> + static const char suffixes[] = { 'B', 'K', 'M', 'G', 'T', 'P', 'E' };
> + unsigned long div;
> + int i;
> +
> + frexp(val, &i);
The ignored return value is in [0.5,1), and multiplying it by 2^i yields
val. i is close to the binary logarithm.
> + i /= 10;
Now it's close to base-1024 logarithm.
Figuring this out requires too much thought for comfort. Recommend
steal the comment from print_type_size(), too.
> + assert(i < sizeof(suffixes));
> + div = 1ULL << (i * 10);
> +
> + return g_strdup_printf("%0.3g %c%s", val / div,
> + suffixes[i], i ? "B" : "");
The conditional is a bit confusing. To avoid it, we could make
suffixes[] an array of strings, with suffixes[0] = "".
> +}
