arch/arm/lib/findbit.S

Source file repositories/reference/linux-study-clean/arch/arm/lib/findbit.S

File Facts

System
Linux kernel
Corpus path
arch/arm/lib/findbit.S
Extension
.S
Size
3126 bytes
Lines
140
Domain
Architecture Layer
Bucket
arch/arm
Inferred role
Architecture Layer: arch/arm
Status
atlas-only

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

#include <linux/linkage.h>
#include <asm/assembler.h>
#include <asm/unwind.h>
                .text

#ifdef __ARMEB__
#define SWAB_ENDIAN le
#else
#define SWAB_ENDIAN be
#endif

		.macro	find_first, endian, set, name
ENTRY(_find_first_\name\()bit_\endian)
	UNWIND(	.fnstart)
		teq	r1, #0
		beq	3f
		mov	r2, #0
1:		ldr	r3, [r0], #4
		.ifeq \set
		mvns	r3, r3			@ invert/test bits
		.else
		movs	r3, r3			@ test bits
		.endif
		.ifc \endian, SWAB_ENDIAN
		bne	.L_found_swab
		.else
		bne	.L_found		@ found the bit?
		.endif
		add	r2, r2, #32		@ next index
2:		cmp	r2, r1			@ any more?
		blo	1b
3:		mov	r0, r1			@ no more bits
		ret	lr
	UNWIND(	.fnend)
ENDPROC(_find_first_\name\()bit_\endian)
		.endm

		.macro	find_next, endian, set, name
ENTRY(_find_next_\name\()bit_\endian)
	UNWIND(	.fnstart)
		cmp	r2, r1
		bhs	3b
		mov	ip, r2, lsr #5		@ word index
		add	r0, r0, ip, lsl #2
		ands	ip, r2, #31		@ bit position
		beq	1b
		ldr	r3, [r0], #4
		.ifeq \set
		mvn	r3, r3			@ invert bits
		.endif
		.ifc \endian, SWAB_ENDIAN
		rev_l	r3, ip
		.if	.Lrev_l_uses_tmp
		@ we need to recompute ip because rev_l will have overwritten
		@ it.
		and	ip, r2, #31		@ bit position
		.endif
		.endif
		movs	r3, r3, lsr ip		@ shift off unused bits
		bne	.L_found
		orr	r2, r2, #31		@ no zero bits
		add	r2, r2, #1		@ align bit pointer
		b	2b			@ loop for next bit
	UNWIND(	.fnend)
ENDPROC(_find_next_\name\()bit_\endian)
		.endm

		.macro	find_bit, endian, set, name
		find_first \endian, \set, \name
		find_next  \endian, \set, \name

Annotation

Implementation Notes