Re: [Qemu-devel] [PATCH v7 2/4] utils: provide size_to_str()

[Peter Xu <peterx@redhat.com>]

On Thu, May 11, 2017 at 02:05:26PM +0100, Dr. David Alan Gilbert wrote:
> * Peter Xu (peterx@redhat.com) wrote:
> > Moving the algorithm from print_type_size() into size_to_str() so that
> > other component can also leverage it. With that, refactor
> > print_type_size().
> > 
> > Reviewed-by: Markus Armbruster <armbru@redhat.com>
> > Signed-off-by: Peter Xu <peterx@redhat.com>
> > ---
> >  include/qemu-common.h        |  1 +
> >  qapi/string-output-visitor.c | 22 ++++++----------------
> >  util/cutils.c                | 26 ++++++++++++++++++++++++++
> >  3 files changed, 33 insertions(+), 16 deletions(-)
> > 
> > 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/qapi/string-output-visitor.c b/qapi/string-output-visitor.c
> > index 94ac821..53c2175 100644
> > --- a/qapi/string-output-visitor.c
> > +++ b/qapi/string-output-visitor.c
> > @@ -211,10 +211,8 @@ static void print_type_size(Visitor *v, const char *name, uint64_t *obj,
> >                              Error **errp)
> >  {
> >      StringOutputVisitor *sov = to_sov(v);
> > -    static const char suffixes[] = { 'B', 'K', 'M', 'G', 'T', 'P', 'E' };
> > -    uint64_t div, val;
> > -    char *out;
> > -    int i;
> > +    uint64_t val;
> > +    char *out, *psize;
> >  
> >      if (!sov->human) {
> >          out = g_strdup_printf("%"PRIu64, *obj);
> > @@ -223,19 +221,11 @@ static void print_type_size(Visitor *v, const char *name, uint64_t *obj,
> >      }
> >  
> >      val = *obj;
> > -
> > -    /* The exponent (returned in i) minus one gives us
> > -     * floor(log2(val * 1024 / 1000).  The correction makes us
> > -     * switch to the higher power when the integer part is >= 1000.
> > -     */
> > -    frexp(val / (1000.0 / 1024.0), &i);
> > -    i = (i - 1) / 10;
> > -    assert(i < ARRAY_SIZE(suffixes));
> > -    div = 1ULL << (i * 10);
> > -
> > -    out = g_strdup_printf("%"PRIu64" (%0.3g %c%s)", val,
> > -                          (double)val/div, suffixes[i], i ? "iB" : "");
> > +    psize = size_to_str(val);
> > +    out = g_strdup_printf("%"PRIu64" (%s)", val, psize);
> >      string_output_set(sov, out);
> > +
> > +    g_free(psize);
> >  }
> >  
> >  static void print_type_bool(Visitor *v, const char *name, bool *obj,
> > diff --git a/util/cutils.c b/util/cutils.c
> > index 50ad179..fa5ddec 100644
> > --- a/util/cutils.c
> > +++ b/util/cutils.c
> > @@ -619,3 +619,29 @@ const char *qemu_ether_ntoa(const MACAddr *mac)
> >  
> >      return ret;
> >  }
> > +
> > +/*
> > + * Return human readable string for size @val.
> > + * @val must be between (-1000Eib, 1000EiB), exclusively.
> > + * Use IEC binary units like KiB, MiB, and so forth.
> > + * Caller is responsible for passing it to g_free().
> > + */
> > +char *size_to_str(double val)
> > +{
> > +    static const char *suffixes[] = { "", "Ki", "Mi", "Gi", "Ti", "Pi", "Ei" };
> > +    unsigned long div;
> > +    int i;
> > +
> > +    /*
> > +     * The exponent (returned in i) minus one gives us
> > +     * floor(log2(val * 1024 / 1000).  The correction makes us
> > +     * switch to the higher power when the integer part is >= 1000.
> > +     * (see e41b509d68afb1f for more info)
> > +     */
> > +    frexp(val / (1000.0 / 1024.0), &i);
> > +    i = (i - 1) / 10;
> > +    assert(i < ARRAY_SIZE(suffixes));
> 
> Because your code takes a double, where as Paolo's only takes uint's,
> I think you have to be careful to check that i >= 0  as well,  for
> example, what would happen if someone did size_to_str(1.0/100.0) ?

Yes, you are right.

Let me stick to uint64_t then, after all double helps little in dump
sizes... /me chose an unwise parameter type.

And then it's safe to directly remove the assert() in this patch,
because even UINT64_MAX is only 16 EiB. Then I can further drop the
last patch...

I'll resend. Thanks,

-- 
Peter Xu