arch/arc/include/asm/bitops.h

Source file repositories/reference/linux-study-clean/arch/arc/include/asm/bitops.h

File Facts

System
Linux kernel
Corpus path
arch/arc/include/asm/bitops.h
Extension
.h
Size
3870 bytes
Lines
200
Domain
Architecture Layer
Bucket
arch/arc
Inferred role
Architecture Layer: implementation source
Status
source implementation candidate

Why This File Exists

CPU and platform-specific kernel glue: boot entry, traps, syscall entry, interrupts, page tables, context switch, and low-level barriers.

Dependency Surface

Detected Declarations

Annotated Snippet

#ifndef _ASM_BITOPS_H
#define _ASM_BITOPS_H

#ifndef _LINUX_BITOPS_H
#error only <linux/bitops.h> can be included directly
#endif

#ifndef __ASSEMBLER__

#include <linux/types.h>
#include <linux/compiler.h>

#ifdef CONFIG_ISA_ARCOMPACT

/*
 * Count the number of zeros, starting from MSB
 * Helper for fls( ) friends
 * This is a pure count, so (1-32) or (0-31) doesn't apply
 * It could be 0 to 32, based on num of 0's in there
 * clz(0x8000_0000) = 0, clz(0xFFFF_FFFF)=0, clz(0) = 32, clz(1) = 31
 */
static inline __attribute__ ((const)) int clz(unsigned int x)
{
	unsigned int res;

	__asm__ __volatile__(
	"	norm.f  %0, %1		\n"
	"	mov.n   %0, 0		\n"
	"	add.p   %0, %0, 1	\n"
	: "=r"(res)
	: "r"(x)
	: "cc");

	return res;
}

static inline int constant_fls(unsigned int x)
{
	int r = 32;

	if (!x)
		return 0;
	if (!(x & 0xffff0000u)) {
		x <<= 16;
		r -= 16;
	}
	if (!(x & 0xff000000u)) {
		x <<= 8;
		r -= 8;
	}
	if (!(x & 0xf0000000u)) {
		x <<= 4;
		r -= 4;
	}
	if (!(x & 0xc0000000u)) {
		x <<= 2;
		r -= 2;
	}
	if (!(x & 0x80000000u))
		r -= 1;
	return r;
}

/*
 * fls = Find Last Set in word
 * @result: [1-32]
 * fls(1) = 1, fls(0x80000000) = 32, fls(0) = 0
 */
static inline __attribute__ ((const)) int fls(unsigned int x)
{
	if (__builtin_constant_p(x))
	       return constant_fls(x);

	return 32 - clz(x);
}

/*
 * __fls: Similar to fls, but zero based (0-31)
 */
static inline __attribute__ ((const)) unsigned long __fls(unsigned long x)
{
	if (!x)
		return 0;
	else
		return fls(x) - 1;
}

/*
 * ffs = Find First Set in word (LSB to MSB)
 * @result: [1-32], 0 if all 0's

Annotation

Implementation Notes