Commit e41b509d authored by Paolo Bonzini's avatar Paolo Bonzini Committed by Andreas Färber
Browse files

qapi: Refine human printing of sizes 



This fixes several bugs or shortcomings of the previous pretty-printer.
In particular:

* use PRIu64 instead of casting to long long

* the exact value is included too

* the correct unit of measure (MiB, GiB, etc.) is used.  PiB and EiB
are added too.

* due to an off-by-one error, 512*2^30 was printed as 0.500MiB rather than
512MiB.  floor(log2(val)) is equal to 63 - clz(val), while the code used 64.

* The desired specification is %g rather than %f, which always uses three
decimals in the current code.  However %g would switch to scientific
notation when the integer part is >= 1000 (e.g. 1000*2^30).  To keep the
code simple, switch to the higher power when the integer part is >= 1000;
overflow is avoided by using frexp instead of clz.

Suggested-by: default avatarEric Blake <eblake@redhat.com>
Reviewed-by: default avatarIgor Mammedov <imammedo@redhat.com>
Reviewed-by: default avatarEric Blake <eblake@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarAndreas Färber <afaerber@suse.de>
parent 85ca1202

qapi/string-output-visitor.c

+12 −11
Original line number Diff line number Diff line
@@ -15,6 +15,7 @@ 
#include "qapi/visitor-impl.h"

#include "qapi/qmp/qerror.h"

#include "qemu/host-utils.h"

#include <math.h>



struct StringOutputVisitor

{
@@ -47,30 +48,30 @@ static void print_type_size(Visitor *v, uint64_t *obj, const char *name, 
                           Error **errp)

{

    StringOutputVisitor *sov = DO_UPCAST(StringOutputVisitor, visitor, v);

    static const char suffixes[] = { 'B', 'K', 'M', 'G', 'T' };

    static const char suffixes[] = { 'B', 'K', 'M', 'G', 'T', 'P', 'E' };

    uint64_t div, val;

    char *out;

    int i;



    if (!sov->human) {

        out = g_strdup_printf("%llu", (long long) *obj);

        out = g_strdup_printf("%"PRIu64, *obj);

        string_output_set(sov, out);

        return;

    }



    val = *obj;



    /* Compute floor(log2(val)).  */

    i = 64 - clz64(val);



    /* Find the power of 1024 that we'll display as the units.  */

    i /= 10;

    if (i >= ARRAY_SIZE(suffixes)) {

        i = ARRAY_SIZE(suffixes) - 1;

    }

    /* 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("%0.03f%c", (double)val/div, suffixes[i]);

    out = g_strdup_printf("%"PRIu64" (%0.3g %c%s)", val,

                          (double)val/div, suffixes[i], i ? "iB" : "");

    string_output_set(sov, out);

}