On Mon, Jul 24, 2017 at 11:01 AM, Matt Brown
<matthew.brown....@gmail.com> wrote:
> This adds emulations for the popcntb, popcntw, and popcntd instructions.
> Tested for correctness against the popcnt{b,w,d} instructions on ppc64le.
>
> Signed-off-by: Matt Brown <matthew.brown....@gmail.com>
> ---
> v2:
> - fixed opcodes
> - fixed typecasting
> - fixed bitshifting error for both 32 and 64bit arch
> ---
> arch/powerpc/lib/sstep.c | 43 ++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 42 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
> index 87d277f..e6a16a3 100644
> --- a/arch/powerpc/lib/sstep.c
> +++ b/arch/powerpc/lib/sstep.c
> @@ -612,6 +612,35 @@ static nokprobe_inline void do_cmpb(struct pt_regs
> *regs, unsigned long v1,
> regs->gpr[rd] = out_val;
> }
>
> +/*
> + * The size parameter is used to adjust the equivalent popcnt instruction.
> + * popcntb = 8, popcntw = 32, popcntd = 64
> + */
> +static nokprobe_inline void do_popcnt(struct pt_regs *regs, unsigned long v1,
> + int size, int ra)
> +{
> + unsigned long long high, low, mask;
> + unsigned int n;
> + int i, j;
> +
> + high = 0;
> + low = 0;
> +
> + for (i = 0; i < (64 / size); i++) {
> + n = 0;
> + for (j = 0; j < size; j++) {
> + mask = 1UL << (j + (i * size));
> + if (v1 & mask)
> + n++;
> + }
> + if ((i * size) < 32)
> + low |= n << (i * size);
> + else
> + high |= n << ((i * size) - 32);
> + }
> + regs->gpr[ra] = (high << 32) | low;
> +}
There's a way to do it in very efficient way via the Giles-Miller
method of side-ways addition
Please see
http://opensourceforu.com/2012/06/power-programming-bitwise-tips-tricks/
and lib/hweight.c, you can reuse the code from lib/hweight.c
Balbir Singh
