On Thu, 30 Jan 2014 17:42:25 +0100
Paolo Bonzini <pbonz...@redhat.com> wrote:
> 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 <ebl...@redhat.com>
> Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
> ---
> qapi/string-output-visitor.c | 23 ++++++++++++-----------
> 1 file changed, 12 insertions(+), 11 deletions(-)
>
> diff --git a/qapi/string-output-visitor.c b/qapi/string-output-visitor.c
> index 67a8798..95dd8fa 100644
> --- a/qapi/string-output-visitor.c
> +++ b/qapi/string-output-visitor.c
> @@ -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" : "");
ERROR: code indent should never use tabs
#81: FILE: qapi/string-output-visitor.c:74:
+^I^I^I (double)val/div, suffixes[i], i ? "iB" : "");$
> string_output_set(sov, out);
> }
>
