tools/include/asm-generic/bitops/__ffs.h

Source file repositories/reference/linux-study-clean/tools/include/asm-generic/bitops/__ffs.h

File Facts

System
Linux kernel
Corpus path
tools/include/asm-generic/bitops/__ffs.h
Extension
.h
Size
852 bytes
Lines
46
Domain
Support Tooling And Documentation
Bucket
tools
Inferred role
Support Tooling And Documentation: implementation source
Status
source implementation candidate

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

Detected Declarations

Annotated Snippet

#ifndef _TOOLS_LINUX_ASM_GENERIC_BITOPS___FFS_H_
#define _TOOLS_LINUX_ASM_GENERIC_BITOPS___FFS_H_

#include <asm/types.h>
#include <asm/bitsperlong.h>

/**
 * __ffs - find first bit in word.
 * @word: The word to search
 *
 * Undefined if no bit exists, so code should check against 0 first.
 */
static __always_inline unsigned int __ffs(unsigned long word)
{
	unsigned int num = 0;

#if __BITS_PER_LONG == 64
	if ((word & 0xffffffff) == 0) {
		num += 32;
		word >>= 32;
	}
#endif
	if ((word & 0xffff) == 0) {
		num += 16;
		word >>= 16;
	}
	if ((word & 0xff) == 0) {
		num += 8;
		word >>= 8;
	}
	if ((word & 0xf) == 0) {
		num += 4;
		word >>= 4;
	}
	if ((word & 0x3) == 0) {
		num += 2;
		word >>= 2;
	}
	if ((word & 0x1) == 0)
		num += 1;
	return num;
}

#endif /* _TOOLS_LINUX_ASM_GENERIC_BITOPS___FFS_H_ */

Annotation

Implementation Notes