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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465666768697071727374757677787980/* SPDX-License-Identifier: GPL-2.0 */#ifndef __LINUX_STRINGHASH_H#define __LINUX_STRINGHASH_H
#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/libsesquipedalianism.so.3.141.) */
/* * 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 longpartial_name_hash(unsigned long c, unsigned long prevhash){ return (prevhash + (c << 4) + (c >> 4)) * 11;}
/* * 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 int end_name_hash(unsigned long hash){ return hash_long(hash, 32);}
/* * 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 */