在 2016年03月28日 14:51, Sam Ravnborg 写道:
diff --git a/include/asm-generic/bitops/arch_parity.h b/include/asm-generic/bitops/arch_parity.h
new file mode 100644
index 0000000..cddc555
--- /dev/null
+++ b/include/asm-generic/bitops/arch_parity.h
@@ -0,0 +1,39 @@
+#ifndef _ASM_GENERIC_BITOPS_ARCH_PARITY_H_
+#define _ASM_GENERIC_BITOPS_ARCH_PARITY_H_
+
+#include <asm/types.h>
+
+/*
+ * Refrence to 'https://graphics.stanford.edu/~seander/bithacks.html#ParityParallel'.
+ */
+
+static inline unsigned int __arch_parity4(unsigned int w)
+{
+ w &= 0xf;
+ return (0x6996 >> w) & 1;
+}
+
+static inline unsigned int __arch_parity8(unsigned int w)
+{
+ w ^= w >> 4;
+ return __arch_parity4(w);
+}
+
+static inline unsigned int __arch_parity16(unsigned int w)
+{
+ w ^= w >> 8;
+ return __arch_parity8(w);
+}
+
+static inline unsigned int __arch_parity32(unsigned int w)
+{
+ w ^= w >> 16;
+ return __arch_parity16(w);
+}
+
+static inline unsigned int __arch_parity64(__u64 w)
+{
+ return __arch_parity32((unsigned int)(w >> 32) ^ (unsigned int)w);
+}
Defining these as static inlines in asm-generic prevent an architecture
from selecting between a more optimal asm version or the generic version
at run-time.
sparc would benefit from this as only some sparc chips supports popc.
See how this is done for hweight*
Sam
Thanks. I will try.
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