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Subject[PATCH 04/10] Change hash_64() return value to 32 bits
That's all that's ever asked for, and it makes the return
type of hash_long() consistent.

It also allows (upcoming patch) an optimized implementation
of hash_64 on 32-bit machines.

There's a WARN_ON in there in case I missed anything. Most callers pass
a compile-time constant bits and will have no run-time overhead.

Signed-off-by: George Spelvin <linux@sciencehorizons.net>
---
include/linux/hash.h | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/include/linux/hash.h b/include/linux/hash.h
index 79c52fa8..b9201c33 100644
--- a/include/linux/hash.h
+++ b/include/linux/hash.h
@@ -48,7 +48,7 @@
#define GOLDEN_RATIO_32 0x61C88647
#define GOLDEN_RATIO_64 0x61C8864680B583EBull

-static __always_inline u64 hash_64(u64 val, unsigned int bits)
+static __always_inline u32 hash_64(u64 val, unsigned int bits)
{
u64 hash = val;

@@ -71,8 +71,14 @@ static __always_inline u64 hash_64(u64 val, unsigned int bits)
hash += n;
#endif

+ if (__builtin_constant_p(bits > 32 || bits == 0)) {
+ BUILD_BUG_ON(bits > 32 || bits == 0);
+ } else {
+ WARN_ON(bits > 32 || bits == 0);
+ }
+
/* High bits are more random, so use them. */
- return hash >> (64 - bits);
+ return (u32)(hash >> (64 - bits));
}

static inline u32 hash_32(u32 val, unsigned int bits)
@@ -84,7 +90,7 @@ static inline u32 hash_32(u32 val, unsigned int bits)
return hash >> (32 - bits);
}

-static inline unsigned long hash_ptr(const void *ptr, unsigned int bits)
+static inline u32 hash_ptr(const void *ptr, unsigned int bits)
{
return hash_long((unsigned long)ptr, bits);
}
--
2.8.1
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