JFIF$        dd7 

Viewing File: /usr/src/kernels/5.14.0-570.32.1.el9_6.x86_64/tools/include/linux/hash.h

#ifndef _LINUX_HASH_H
#define _LINUX_HASH_H
/* Fast hashing routine for ints,  longs and pointers.
   (C) 2002 Nadia Yvette Chambers, IBM */

#include <asm/types.h>
#include <linux/compiler.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
 * were actively bad for hashing), but the name remains.
 */
#if BITS_PER_LONG == 32
#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_32
#define hash_long(val, bits) hash_32(val, bits)
#elif BITS_PER_LONG == 64
#define hash_long(val, bits) hash_64(val, bits)
#define GOLDEN_RATIO_PRIME GOLDEN_RATIO_64
#else
#error Wordsize not 32 or 64
#endif

/*
 * This hash multiplies the input by a large odd number and takes the
 * high bits.  Since multiplication propagates changes to the most
 * significant end only, it is essential that the high bits of the
 * product be used for the hash value.
 *
 * Chuck Lever verified the effectiveness of this technique:
 * http://www.citi.umich.edu/techreports/reports/citi-tr-00-1.pdf
 *
 * Although a random odd number will do, it turns out that the golden
 * ratio phi = (sqrt(5)-1)/2, or its negative, has particularly nice
 * properties.  (See Knuth vol 3, section 6.4, exercise 9.)
 *
 * These are the negative, (1 - phi) = phi**2 = (3 - sqrt(5))/2,
 * which is very slightly easier to multiply by and makes no
 * difference to the hash distribution.
 */
#define GOLDEN_RATIO_32 0x61C88647
#define GOLDEN_RATIO_64 0x61C8864680B583EBull

#ifdef CONFIG_HAVE_ARCH_HASH
/* This header may use the GOLDEN_RATIO_xx constants */
#include <asm/hash.h>
#endif

/*
 * The _generic versions exist only so lib/test_hash.c can compare
 * the arch-optimized versions with the generic.
 *
 * Note that if you change these, any <asm/hash.h> that aren't updated
 * to match need to have their HAVE_ARCH_* define values updated so the
 * self-test will not false-positive.
 */
#ifndef HAVE_ARCH__HASH_32
#define __hash_32 __hash_32_generic
#endif
static inline u32 __hash_32_generic(u32 val)
{
	return val * GOLDEN_RATIO_32;
}

static inline u32 hash_32(u32 val, unsigned int bits)
{
	/* High bits are more random, so use them. */
	return __hash_32(val) >> (32 - bits);
}

#ifndef HAVE_ARCH_HASH_64
#define hash_64 hash_64_generic
#endif
static __always_inline u32 hash_64_generic(u64 val, unsigned int bits)
{
#if BITS_PER_LONG == 64
	/* 64x64-bit multiply is efficient on all 64-bit processors */
	return val * GOLDEN_RATIO_64 >> (64 - bits);
#else
	/* Hash 64 bits using only 32x32-bit multiply. */
	return hash_32((u32)val ^ __hash_32(val >> 32), bits);
#endif
}

static inline u32 hash_ptr(const void *ptr, unsigned int bits)
{
	return hash_long((unsigned long)ptr, bits);
}

/* This really should be called fold32_ptr; it does no hashing to speak of. */
static inline u32 hash32_ptr(const void *ptr)
{
	unsigned long val = (unsigned long)ptr;

#if BITS_PER_LONG == 64
	val ^= (val >> 32);
#endif
	return (u32)val;
}

#endif /* _LINUX_HASH_H */
Back to Directory  nL+D550H?Mx ,D"v]qv;6*Zqn)ZP0!1 A "#a$2Qr D8 a Ri[f\mIykIw0cuFcRı?lO7к_f˓[C$殷WF<_W ԣsKcëIzyQy/_LKℂ;C",pFA:/]=H  ~,ls/9ć:[=/#f;)x{ٛEQ )~ =𘙲r*2~ a _V=' kumFD}KYYC)({ *g&f`툪ry`=^cJ.I](*`wq1dđ#̩͑0;H]u搂@:~וKL Nsh}OIR*8:2 !lDJVo(3=M(zȰ+i*NAr6KnSl)!JJӁ* %݉?|D}d5:eP0R;{$X'xF@.ÊB {,WJuQɲRI;9QE琯62fT.DUJ;*cP A\ILNj!J۱+O\͔]ޒS߼Jȧc%ANolՎprULZԛerE2=XDXgVQeӓk yP7U*omQIs,K`)6\G3t?pgjrmۛجwluGtfh9uyP0D;Uڽ"OXlif$)&|ML0Zrm1[HXPlPR0'G=i2N+0e2]]9VTPO׮7h(F*癈'=QVZDF,d߬~TX G[`le69CR(!S2!P <0x<!1AQ "Raq02Br#SCTb ?Ζ"]mH5WR7k.ۛ!}Q~+yԏz|@T20S~Kek *zFf^2X*(@8r?CIuI|֓>^ExLgNUY+{.RѪ τV׸YTD I62'8Y27'\TP.6d&˦@Vqi|8-OΕ]ʔ U=TL8=;6c| !qfF3aů&~$l}'NWUs$Uk^SV:U# 6w++s&r+nڐ{@29 gL u"TÙM=6(^"7r}=6YݾlCuhquympǦ GjhsǜNlɻ}o7#S6aw4!OSrD57%|?x>L |/nD6?/8w#[)L7+6〼T ATg!%5MmZ/c-{1_Je"|^$'O&ޱմTrb$w)R$& N1EtdU3Uȉ1pM"N*(DNyd96.(jQ)X 5cQɎMyW?Q*!R>6=7)Xj5`J]e8%t!+'!1Q5 !1 AQaqё#2"0BRb?Gt^## .llQT $v,,m㵜5ubV =sY+@d{N! dnO<.-B;_wJt6;QJd.Qc%p{ 1,sNDdFHI0ГoXшe黅XۢF:)[FGXƹ/w_cMeD,ʡcc.WDtA$j@:) -# u c1<@ۗ9F)KJ-hpP]_x[qBlbpʖw q"LFGdƶ*s+ډ_Zc"?%t[IP 6J]#=ɺVvvCGsGh1 >)6|ey?Lӣm,4GWUi`]uJVoVDG< SB6ϏQ@ TiUlyOU0kfV~~}SZ@*WUUi##; s/[=!7}"WN]'(L! ~y5g9T̅JkbM' +s:S +B)v@Mj e Cf jE 0Y\QnzG1д~Wo{T9?`Rmyhsy3!HAD]mc1~2LSu7xT;j$`}4->L#vzŏILS ֭T{rjGKC;bpU=-`BsK.SFw4Mq]ZdHS0)tLg