Re: [PATCH 01/31] bitops: add parity functions

Sam Ravnborg
2016-03-27T12:44:12Z

Hi Zeng.

Looking through the arch specific implementations of __arch_parity().
Some architectures uses #defines, other uses inline static functions.

Any particular reason that you select one approach over the other
in the different cases?

ia64:
+#define __arch_parity32(x) ((unsigned int) __arch_parity64((x) & 0xfffffffful))
+#define __arch_parity16(x) ((unsigned int) __arch_parity64((x) & 0xfffful))
+#define __arch_parity8(x) ((unsigned int) __arch_parity64((x) & 0xfful))
+#define __arch_parity4(x) ((unsigned int) __arch_parity64((x) & 0xful))

tile:
+static inline unsigned int __arch_parity32(unsigned int w)
+{
+ return __builtin_popcount(w) & 1;
+}
+
+static inline unsigned int __arch_parity16(unsigned int w)
+{
+ return __arch_parity32(w & 0xffff);
+}
+
+static inline unsigned int __arch_parity8(unsigned int w)
+{
+ return __arch_parity32(w & 0xff);
+}
+
+static inline unsigned int __arch_parity4(unsigned int w)
+{
+ return __arch_parity32(w & 0xf);
+}

Just two examples.

Adding the parity helpers seems like veny nice simplifications.

A few comments to some of those I looked at.
(I am not subscribed to lkml, so you get it as comments here)

[PATCH 21/31] mtd: use parity16 in ssfdc.c
The original code semes to check that the parity equals the
value of first bit in the address.
This seems lost after the conversion.

[PATCH 20/31] scsi: use parity32 in isci/phy.c
+ if (parity32(phy_cap.all))
phy_cap.parity = 1;
Could be written like this - simpler IMO:
phy_cap.parity = parity32(phy_cap.all);

Sam