From: Sukadev Bhattiprolu
> When checking whether a bit representing a register is set in
> sample_regs, a 64-bit mask, use 64-bit value (1LL).
>
> Signed-off-by: Sukadev Bhattiprolu <suka...@linux.vnet.ibm.com>
> ---
> tools/perf/util/unwind.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/util/unwind.c b/tools/perf/util/unwind.c
> index 742f23b..2b888c6 100644
> --- a/tools/perf/util/unwind.c
> +++ b/tools/perf/util/unwind.c
> @@ -396,11 +396,11 @@ static int reg_value(unw_word_t *valp, struct regs_dump
> *regs, int id,
> {
> int i, idx = 0;
>
> - if (!(sample_regs & (1 << id)))
> + if (!(sample_regs & (1LL << id)))
> return -EINVAL;
>
> for (i = 0; i < id; i++) {
> - if (sample_regs & (1 << i))
> + if (sample_regs & (1LL << i))
> idx++;
> }
There are much faster ways to count the number of set bits, especially
if you might need to check a significant number of bits.
There might even be a function defined somewhere to do it.
Basically you just add up the bits, for 16 bit it would be:
val = (val & 0x5555) + (val >> 1) & 0x5555;
val = (val & 0x3333) + (val >> 2) & 0x3333;
val = (val & 0x0f0f) + (val >> 4) & 0x0f0f;
val = (val & 0x00ff) + (val >> 8) & 0x00ff;
As the size of the work increases the improvement is more significant.
(Some of the later masking can probably be proven unnecessary.)
David
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