arch/arm/lib/csumpartial.S

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

File Facts

System
Linux kernel
Corpus path
arch/arm/lib/csumpartial.S
Extension
.S
Size
2976 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>

		.text

/*
 * Function: __u32 csum_partial(const char *src, int len, __u32 sum)
 * Params  : r0 = buffer, r1 = len, r2 = checksum
 * Returns : r0 = new checksum
 */

buf	.req	r0
len	.req	r1
sum	.req	r2
td0	.req	r3
td1	.req	r4	@ save before use
td2	.req	r5	@ save before use
td3	.req	lr

.Lzero:		mov	r0, sum
		add	sp, sp, #4
		ldr	pc, [sp], #4

		/*
		 * Handle 0 to 7 bytes, with any alignment of source and
		 * destination pointers.  Note that when we get here, C = 0
		 */
.Lless8:		teq	len, #0			@ check for zero count
		beq	.Lzero

		/* we must have at least one byte. */
		tst	buf, #1			@ odd address?
		movne	sum, sum, ror #8
		ldrbne	td0, [buf], #1
		subne	len, len, #1
		adcsne	sum, sum, td0, put_byte_1

.Lless4:		tst	len, #6
		beq	.Lless8_byte

		/* we are now half-word aligned */

.Lless8_wordlp:
#if __LINUX_ARM_ARCH__ >= 4
		ldrh	td0, [buf], #2
		sub	len, len, #2
#else
		ldrb	td0, [buf], #1
		ldrb	td3, [buf], #1
		sub	len, len, #2
#ifndef __ARMEB__
		orr	td0, td0, td3, lsl #8
#else
		orr	td0, td3, td0, lsl #8
#endif
#endif
		adcs	sum, sum, td0
		tst	len, #6
		bne	.Lless8_wordlp

.Lless8_byte:	tst	len, #1			@ odd number of bytes
		ldrbne	td0, [buf], #1		@ include last byte
		adcsne	sum, sum, td0, put_byte_0	@ update checksum

.Ldone:		adc	r0, sum, #0		@ collect up the last carry
		ldr	td0, [sp], #4
		tst	td0, #1			@ check buffer alignment
		movne	r0, r0, ror #8		@ rotate checksum by 8 bits
		ldr	pc, [sp], #4		@ return

Annotation

Implementation Notes