在 2016年04月06日 18:13, Borislav Petkov 写道:
On Wed, Apr 06, 2016 at 05:14:45PM +0800, [email protected] wrote:
From: Zhaoxiu Zeng <[email protected]>
Use alternatives, lifted from arch_hweight
Signed-off-by: Zhaoxiu Zeng <[email protected]>
---
arch/x86/include/asm/arch_hweight.h | 5 ++
arch/x86/include/asm/arch_parity.h | 102 ++++++++++++++++++++++++++++++++++++
arch/x86/include/asm/bitops.h | 4 +-
arch/x86/lib/Makefile | 8 +++
arch/x86/lib/parity.c | 32 ++++++++++++
5 files changed, 150 insertions(+), 1 deletion(-)
create mode 100644 arch/x86/include/asm/arch_parity.h
create mode 100644 arch/x86/lib/parity.c
...
+static __always_inline unsigned int __arch_parity32(unsigned int w)
+{
+ unsigned int res;
+
+ asm(ALTERNATIVE("call __sw_parity32", POPCNT32 "; and $1, %0",
X86_FEATURE_POPCNT)
+ : "="REG_OUT (res)
+ : REG_IN (w)
+ : "cc");
So why all that churn instead of simply doing:
static __always_inline unsigned int __arch_parity32(unsigned int w)
{
return hweight32(w) & 1;
}
Ditto for the 64-bit version.
__sw_parity32 is faster than __sw_hweight32.
I don't know how many CPUs do not support the popc, if they are outdated,
use __arch_hweight32 is the easiest way.
