cosmetic changes

2019/include/bug.h

@@ -8,7 +8,8 @@
 #include "likely.h"
 #include "debug.h"
 
-/* inspired by Linux kernel's <asm/bug.h> */
+/* BUG functions inspired by Linux kernel's <asm/bug.h>
+ */
 
 #define panic() exit(0xff)
 

2019/include/hash.h

@@ -2,7 +2,7 @@
 
 #ifndef _BR_HASH_H
 #define _BR_HASH_H
-/* adaptation of Linux kernel's <linux/hash.h>
+/* adaptation of Linux kernel's <linux/hash.h> and <linux/stringhash.h>
  */
 
 /* Fast hashing routine for ints,  longs and pointers.
@@ -11,6 +11,8 @@
 #include <asm/types.h>
 #include <asm/bitsperlong.h>
 #include "bits.h"
+#include "br.h"
+
 /*
  * The "GOLDEN_RATIO_PRIME" is used in ifs/btrfs/brtfs_inode.h and
  * fs/inode.c.  It's not actually prime any more (the previous primes
@@ -98,4 +100,74 @@ static inline u32 hash32_ptr(const void *ptr)
 	return (u32)val;
 }
 
+/*
+ * 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 long
+partial_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 hash_string(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 /* _BR_HASH_H */