Fix bug when both pointers have matching, non-word alignment, and the length
is <= 4 but more than enough to move them over a word boundary. Add comments explaining what each instruction does.
This commit is contained in:
Nick Clifton
parent
b9ce814089
commit
2ce884182c
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@ -1,3 +1,10 @@
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2001-05-25 Nick Clifton <nickc@cambridge.redhat.com>
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* libc/machine/xscale/memcmp.c: Fix bug when both pointers have
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matching, non-word alignment, and the length is <= 4 but more than
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enough to move them over a word boundary.
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Add comments explaining what each instruction does.
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Mon May 7 20:39:25 2001 Christopher Faylor <cgf@cygnus.com>
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* libc/include/sys/stat.h: Revert March 3, Cygwin change.
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@ -8,99 +8,102 @@
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#include "xscale.h"
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int
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memcmp (const void *s1, const void *s2, size_t len)
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memcmp (const void * s1, const void * s2, size_t len)
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{
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int result;
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asm (
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#ifndef __OPTIMIZE_SIZE__
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"
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cmp %2, #0x3
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bls 6f
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and r2, %0, #0x3
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and r3, %1, #0x3
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cmp r2, r3
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bne 6f
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mov lr, %0
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mov r4, %1
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cmp r2, #0x0
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beq 3f
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b 1f
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0:
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ldrb r2, [lr], #1 @ zero_extendqisi2
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" PRELOADSTR("lr") "
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ldrb r3, [r4], #1 @ zero_extendqisi2
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" PRELOADSTR("r4") "
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cmp r2, r3
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bne 5f
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tst lr, #0x3
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beq 3f
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1:
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sub %2, %2, #1
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cmn %2, #0x1
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bne 0b
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b 4f
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cmp %2, #0x3 @ Is the length a multiple of four ?
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bls 6f @ no = goto SLOW CHECK
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and r2, %0, #0x3 @ get alignment of first pointer
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and r3, %1, #0x3 @ get alignment of second pointer
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cmp r2, r3 @ Do the two pointers share the same alignment ?
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bne 6f @ no = goto SLOW CHECK
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mov lr, %0 @ copy first pointer into LR
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mov r4, %1 @ copy second pointer into R4
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cmp r2, #0x0 @ Are we comparing word aligned pointers ?
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beq 3f @ yes = goto START WORD CHECK LOOP
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b 1f @ jump to LOOP TEST
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0: @ LOOP START
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ldrb r2, [lr], #1 @ load byte from LR, post inc.
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" PRELOADSTR("lr") " @ preload
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ldrb r3, [r4], #1 @ load byte from R4, post inc.
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" PRELOADSTR("r4") " @ preload
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cmp r2, r3 @ are the two bytes the same ?
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bne 5f @ no = goto EXIT
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tst lr, #0x3 @ has the LR become word aligned ?
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bne 1f @ no = skip the next test
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cmp %2, #4 @ is the count >= 4 ?
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bhs 3f @ yes = goto START WORD CHECK LOOP
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1: @ LOOP TEST
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sub %2, %2, #1 @ decrement count by one
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cmn %2, #0x1 @ has the count reached -1 ?
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bne 0b @ no = loop back to LOOP START
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b 4f @ goto PASS END
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0:
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cmp %2, #0x7
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bls 3f
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ldmia lr,{r2, r3}
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ldmia r4,{r5, r6}
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sub %2, %2, #0x4
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cmp r2, r5
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bne 1f
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sub %2, %2, #0x4
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add lr, lr, #0x4
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add r4, r4, #0x4
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cmp r3, r6
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beq 0b
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1:
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add %2, %2, #0x4
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sub %0, lr, #0x4
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sub %1, r4, #0x4
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b 6f
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3:
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cmp %2, #0x3
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bls 1f
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ldr r2, [lr], #4
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ldr r3, [r4], #4
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sub %2, %2, #4
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cmp r2, r3
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bne 1f
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0:
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cmp %2, #0x3
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bls 1f
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ldr r2, [lr], #4
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" PRELOADSTR("lr") "
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ldr r3, [r4], #4
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" PRELOADSTR("r4") "
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sub %2, %2, #4
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cmp r2, r3
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beq 0b
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1:
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sub %0, lr, #0x4
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sub %1, r4, #0x4
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add %2, %2, #4
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"
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0: @ ??
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cmp %2, #0x7 @ Is the count a multiple of 8 ?
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bls 3f @ no = goto ???
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ldmia lr,{r2, r3} @ get two words from first pointer, post inc
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ldmia r4,{r5, r6} @ get two words from second pointer, post inc
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sub %2, %2, #0x4 @ decrement count by 4
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cmp r2, r5 @ has the count reached ????
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bne 1f @ no = goto
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sub %2, %2, #0x4 @ decrement the count by 4
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add lr, lr, #0x4 @ add 4 to first pointer
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add r4, r4, #0x4 @ add 4 to second pointer
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cmp r3, r6 @ ???
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beq 0b @ goto ???
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1: @ ??
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add %2, %2, #0x4 @ Add four to count
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sub %0, lr, #0x4 @ decrement first pointer by 4
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sub %1, r4, #0x4 @ decrement second pointer by 4
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b 6f @ goto SLOW CHECK
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3: @ START WORD CHECK LOOP
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cmp %2, #0x3 @ is the count <= 3 ?
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bls 1f @ yes = goto CHECK BYTES BY HAND
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ldr r2, [lr], #4 @ get word from LR, post inc
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ldr r3, [r4], #4 @ get word from R4, post inc
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sub %2, %2, #4 @ decrement count by 4
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cmp r2, r3 @ are the two words the same ?
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bne 1f @ no = goto CHECK WORD CONTENTS
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0: @ WORD CHECK LOOP
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cmp %2, #0x3 @ is the count <= 3 ?
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bls 1f @ yes = goto CHECK BYTES BY HAND
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ldr r2, [lr], #4 @ load word from LR, post inc
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" PRELOADSTR("lr") " @ preload
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ldr r3, [r4], #4 @ load word from R4, post inc
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" PRELOADSTR("r4") " @ preload
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sub %2, %2, #4 @ decrement count by 4
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cmp r2, r3 @ are the two words the same ?
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beq 0b @ yes = goto WORD CHECK LOOP
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1: @ CHECK BYTES BY HAND
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sub %0, lr, #0x4 @ move LR back a word and put into first pointer
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sub %1, r4, #0x4 @ move R4 back a word and put into second pointer
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add %2, %2, #4 @ increment the count by 4
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@ fall through into SLOW CHECK"
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#endif /* !__OPTIMIZE_SIZE__ */
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"
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6:
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sub %2, %2, #1
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cmn %2, #0x1
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beq 4f
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0:
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ldrb r2, [%0], #1 @ zero_extendqisi2
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" PRELOADSTR("%0") "
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ldrb r3, [%1], #1 @ zero_extendqisi2
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" PRELOADSTR("%1") "
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cmp r2, r3
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bne 5f
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sub %2, %2, #1
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cmn %2, #0x1
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bne 0b
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4:
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mov r3, r2
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5:
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rsb %0, r3, r2"
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6: @ SLOW CHECK
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sub %2, %2, #1 @ Decrement the count by one
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cmn %2, #0x1 @ Has the count reached -1 ?
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beq 4f @ Yes - we are finished, goto PASS END
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0: @ LOOP1
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ldrb r2, [%0], #1 @ get byte from first pointer
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" PRELOADSTR("%0") " @ preload first pointer
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ldrb r3, [%1], #1 @ get byte from second pointer
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" PRELOADSTR("%1") " @ preload second pointer
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cmp r2, r3 @ compare the two loaded bytes
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bne 5f @ if they are not equal goto EXIT
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sub %2, %2, #1 @ decremented count by 1
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cmn %2, #0x1 @ has the count reached -1 ?
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bne 0b @ no = then go back to LOOP1
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4: @ PASS END
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mov r3, r2 @ Default return value is 0
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5: @ EXIT
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rsb %0, r3, r2 @ return difference between last two bytes loaded"
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: "=r" (result), "=&r" (s2), "=&r" (len)
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: "0" (s1), "1" (s2), "2" (len)
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: "r2", "r3", "r4", "r5", "r6", "cc", "lr");
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