cachepc-linux

Fork of AMDESE/linux with modifications for CachePC side-channel attack
git clone https://git.sinitax.com/sinitax/cachepc-linux
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stringhash.h (2715B)

      1/* SPDX-License-Identifier: GPL-2.0 */
      2#ifndef __LINUX_STRINGHASH_H
      3#define __LINUX_STRINGHASH_H
      4
      5#include <linux/compiler.h>	/* For __pure */
      6#include <linux/types.h>	/* For u32, u64 */
      7#include <linux/hash.h>
      8
      9/*
     10 * Routines for hashing strings of bytes to a 32-bit hash value.
     11 *
     12 * These hash functions are NOT GUARANTEED STABLE between kernel
     13 * versions, architectures, or even repeated boots of the same kernel.
     14 * (E.g. they may depend on boot-time hardware detection or be
     15 * deliberately randomized.)
     16 *
     17 * They are also not intended to be secure against collisions caused by
     18 * malicious inputs; much slower hash functions are required for that.
     19 *
     20 * They are optimized for pathname components, meaning short strings.
     21 * Even if a majority of files have longer names, the dynamic profile of
     22 * pathname components skews short due to short directory names.
     23 * (E.g. /usr/lib/libsesquipedalianism.so.3.141.)
     24 */
     25
     26/*
     27 * Version 1: one byte at a time.  Example of use:
     28 *
     29 * unsigned long hash = init_name_hash;
     30 * while (*p)
     31 *	hash = partial_name_hash(tolower(*p++), hash);
     32 * hash = end_name_hash(hash);
     33 *
     34 * Although this is designed for bytes, fs/hfsplus/unicode.c
     35 * abuses it to hash 16-bit values.
     36 */
     37
     38/* Hash courtesy of the R5 hash in reiserfs modulo sign bits */
     39#define init_name_hash(salt)		(unsigned long)(salt)
     40
     41/* partial hash update function. Assume roughly 4 bits per character */
     42static inline unsigned long
     43partial_name_hash(unsigned long c, unsigned long prevhash)
     44{
     45	return (prevhash + (c << 4) + (c >> 4)) * 11;
     46}
     47
     48/*
     49 * Finally: cut down the number of bits to a int value (and try to avoid
     50 * losing bits).  This also has the property (wanted by the dcache)
     51 * that the msbits make a good hash table index.
     52 */
     53static inline unsigned int end_name_hash(unsigned long hash)
     54{
     55	return hash_long(hash, 32);
     56}
     57
     58/*
     59 * Version 2: One word (32 or 64 bits) at a time.
     60 * If CONFIG_DCACHE_WORD_ACCESS is defined (meaning <asm/word-at-a-time.h>
     61 * exists, which describes major Linux platforms like x86 and ARM), then
     62 * this computes a different hash function much faster.
     63 *
     64 * If not set, this falls back to a wrapper around the preceding.
     65 */
     66extern unsigned int __pure full_name_hash(const void *salt, const char *, unsigned int);
     67
     68/*
     69 * A hash_len is a u64 with the hash of a string in the low
     70 * half and the length in the high half.
     71 */
     72#define hashlen_hash(hashlen) ((u32)(hashlen))
     73#define hashlen_len(hashlen)  ((u32)((hashlen) >> 32))
     74#define hashlen_create(hash, len) ((u64)(len)<<32 | (u32)(hash))
     75
     76/* Return the "hash_len" (hash and length) of a null-terminated string */
     77extern u64 __pure hashlen_string(const void *salt, const char *name);
     78
     79#endif	/* __LINUX_STRINGHASH_H */