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qapi: Refine human printing of sizes

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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: Eric Blake <eblake@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
This commit is contained in:
Paolo Bonzini 2014-02-08 11:01:57 +01:00 committed by Andreas Färber
parent 85ca1202d1
commit e41b509d68
1 changed files with 12 additions and 11 deletions
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23
qapi/string-output-visitor.c
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@ -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);
}