74 lines
2.0 KiB
Diff
74 lines
2.0 KiB
Diff
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---
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usr/target.h | 59 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
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1 file changed, 58 insertions(+), 1 deletion(-)
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--- a/usr/target.h
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+++ b/usr/target.h
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@@ -3,8 +3,65 @@
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#include <limits.h>
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#define BITS_PER_LONG (ULONG_MAX == 0xFFFFFFFFUL ? 32 : 64)
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-#include <linux/hash.h>
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+#ifndef _LINUX_HASH_H
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+#define _LINUX_HASH_H
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+/* Fast hashing routine for a long.
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+ (C) 2002 William Lee Irwin III, IBM */
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+
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+/*
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+ * Knuth recommends primes in approximately golden ratio to the maximum
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+ * integer representable by a machine word for multiplicative hashing.
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+ * Chuck Lever verified the effectiveness of this technique:
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+ * http://www.citi.umich.edu/techreports/reports/citi-tr-00-1.pdf
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+ *
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+ * These primes are chosen to be bit-sparse, that is operations on
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+ * them can use shifts and additions instead of multiplications for
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+ * machines where multiplications are slow.
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+ */
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+#if BITS_PER_LONG == 32
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+/* 2^31 + 2^29 - 2^25 + 2^22 - 2^19 - 2^16 + 1 */
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+#define GOLDEN_RATIO_PRIME 0x9e370001UL
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+#elif BITS_PER_LONG == 64
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+/* 2^63 + 2^61 - 2^57 + 2^54 - 2^51 - 2^18 + 1 */
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+#define GOLDEN_RATIO_PRIME 0x9e37fffffffc0001UL
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+#else
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+#error Define GOLDEN_RATIO_PRIME for your wordsize.
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+#endif
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+
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+static inline unsigned long hash_long(unsigned long val, unsigned int bits)
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+{
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+ unsigned long hash = val;
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+
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+#if BITS_PER_LONG == 64
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+ /* Sigh, gcc can't optimise this alone like it does for 32 bits. */
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+ unsigned long n = hash;
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+ n <<= 18;
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+ hash -= n;
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+ n <<= 33;
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+ hash -= n;
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+ n <<= 3;
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+ hash += n;
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+ n <<= 3;
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+ hash -= n;
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+ n <<= 4;
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+ hash += n;
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+ n <<= 2;
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+ hash += n;
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+#else
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+ /* On some cpus multiply is faster, on others gcc will do shifts */
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+ hash *= GOLDEN_RATIO_PRIME;
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+#endif
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+
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+ /* High bits are more random, so use them. */
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+ return hash >> (BITS_PER_LONG - bits);
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+}
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+
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+static inline unsigned long hash_ptr(void *ptr, unsigned int bits)
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+{
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+ return hash_long((unsigned long)ptr, bits);
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+}
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+#endif /* _LINUX_HASH_H */
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#define HASH_ORDER 4
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#define hashfn(val) hash_long((unsigned long) (val), HASH_ORDER)
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