cregit-Linux how code gets into the kernel

Release 4.12 include/linux/stringhash.h

Directory: include/linux


#include <linux/compiler.h>	/* For __pure */
#include <linux/types.h>	/* For u32, u64 */
#include <linux/hash.h>

 * Routines for hashing strings of bytes to a 32-bit hash value.
 * These hash functions are NOT GUARANTEED STABLE between kernel
 * versions, architectures, or even repeated boots of the same kernel.
 * (E.g. they may depend on boot-time hardware detection or be
 * deliberately randomized.)
 * They are also not intended to be secure against collisions caused by
 * malicious inputs; much slower hash functions are required for that.
 * They are optimized for pathname components, meaning short strings.
 * Even if a majority of files have longer names, the dynamic profile of
 * pathname components skews short due to short directory names.
 * (E.g. /usr/lib/

 * Version 1: one byte at a time.  Example of use:
 * unsigned long hash = init_name_hash;
 * while (*p)
 *      hash = partial_name_hash(tolower(*p++), hash);
 * hash = end_name_hash(hash);
 * Although this is designed for bytes, fs/hfsplus/unicode.c
 * abuses it to hash 16-bit values.

/* Hash courtesy of the R5 hash in reiserfs modulo sign bits */

#define init_name_hash(salt)		(unsigned long)(salt)

/* partial hash update function. Assume roughly 4 bits per character */

static inline unsigned long partial_name_hash(unsigned long c, unsigned long prevhash) { return (prevhash + (c << 4) + (c >> 4)) * 11; }


George Spelvin35100.00%1100.00%

/* * Finally: cut down the number of bits to a int value (and try to avoid * losing bits). This also has the property (wanted by the dcache) * that the msbits make a good hash table index. */
static inline unsigned long end_name_hash(unsigned long hash) { return __hash_32((unsigned int)hash); }


George Spelvin22100.00%2100.00%

/* * Version 2: One word (32 or 64 bits) at a time. * If CONFIG_DCACHE_WORD_ACCESS is defined (meaning <asm/word-at-a-time.h> * exists, which describes major Linux platforms like x86 and ARM), then * this computes a different hash function much faster. * * If not set, this falls back to a wrapper around the preceding. */ extern unsigned int __pure full_name_hash(const void *salt, const char *, unsigned int); /* * A hash_len is a u64 with the hash of a string in the low * half and the length in the high half. */ #define hashlen_hash(hashlen) ((u32)(hashlen)) #define hashlen_len(hashlen) ((u32)((hashlen) >> 32)) #define hashlen_create(hash, len) ((u64)(len)<<32 | (u32)(hash)) /* Return the "hash_len" (hash and length) of a null-terminated string */ extern u64 __pure hashlen_string(const void *salt, const char *name); #endif /* __LINUX_STRINGHASH_H */

Overall Contributors

George Spelvin13690.67%375.00%
Linus Torvalds149.33%125.00%
Directory: include/linux
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