arch/arc/lib/strchr-700.S

Source file repositories/reference/linux-study-clean/arch/arc/lib/strchr-700.S

File Facts

System
Linux kernel
Corpus path
arch/arc/lib/strchr-700.S
Extension
.S
Size
2576 bytes
Lines
131
Domain
Architecture Layer
Bucket
arch/arc
Inferred role
Architecture Layer: arch/arc
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

to avoid branches that are hard to predict.  On the other hand, the
   presence of the norm instruction makes it easier to operate on whole
   words branch-free.  */

#include <linux/linkage.h>

ENTRY_CFI(strchr)
	extb_s	r1,r1
	asl	r5,r1,8
	bmsk	r2,r0,1
	or	r5,r5,r1
	mov_s	r3,0x01010101
	breq.d	r2,r0,.Laligned
	asl	r4,r5,16
	sub_s	r0,r0,r2
	asl	r7,r2,3
	ld_s	r2,[r0]
#ifdef __LITTLE_ENDIAN__
	asl	r7,r3,r7
#else
	lsr	r7,r3,r7
#endif
	or	r5,r5,r4
	ror	r4,r3
	sub	r12,r2,r7
	bic_s	r12,r12,r2
	and	r12,r12,r4
	brne.d	r12,0,.Lfound0_ua
	xor	r6,r2,r5
	ld.a	r2,[r0,4]
	sub	r12,r6,r7
	bic	r12,r12,r6
#ifdef __LITTLE_ENDIAN__
	and	r7,r12,r4
	breq	r7,0,.Loop ; For speed, we want this branch to be unaligned.
	b	.Lfound_char ; Likewise this one.
#else
	and	r12,r12,r4
	breq	r12,0,.Loop ; For speed, we want this branch to be unaligned.
	lsr_s	r12,r12,7
	bic 	r2,r7,r6
	b.d	.Lfound_char_b
	and_s	r2,r2,r12
#endif
; /* We require this code address to be unaligned for speed...  */
.Laligned:
	ld_s	r2,[r0]
	or	r5,r5,r4
	ror	r4,r3
; /* ... so that this code address is aligned, for itself and ...  */
.Loop:
	sub	r12,r2,r3
	bic_s	r12,r12,r2
	and	r12,r12,r4
	brne.d	r12,0,.Lfound0
	xor	r6,r2,r5
	ld.a	r2,[r0,4]
	sub	r12,r6,r3
	bic	r12,r12,r6
	and	r7,r12,r4
	breq	r7,0,.Loop /* ... so that this branch is unaligned.  */
	; Found searched-for character.  r0 has already advanced to next word.
#ifdef __LITTLE_ENDIAN__
/* We only need the information about the first matching byte
   (i.e. the least significant matching byte) to be exact,
   hence there is no problem with carry effects.  */
.Lfound_char:
	sub	r3,r7,1
	bic	r3,r3,r7
	norm	r2,r3

Annotation

Implementation Notes