From 2ce884182c6752cf9bcfd72399d7e9e4c5048da0 Mon Sep 17 00:00:00 2001
From: Nick Clifton <nickc@redhat.com>
Date: Fri, 25 May 2001 21:17:06 +0000
Subject: [PATCH] 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.
---
newlib/ChangeLog | 7 ++
newlib/libc/machine/xscale/memcmp.c | 173 ++++++++++++++--------------
2 files changed, 95 insertions(+), 85 deletions(-)
diff --git a/newlib/ChangeLog b/newlib/ChangeLog
index 79f59fb42..5c23dece0 100644
--- a/newlib/ChangeLog
+++ b/newlib/ChangeLog
@@ -1,3 +1,10 @@
+2001-05-25 Nick Clifton <nickc@cambridge.redhat.com>
+
+ * libc/machine/xscale/memcmp.c: 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.
+
Mon May 7 20:39:25 2001 Christopher Faylor <cgf@cygnus.com>
* libc/include/sys/stat.h: Revert March 3, Cygwin change.
diff --git a/newlib/libc/machine/xscale/memcmp.c b/newlib/libc/machine/xscale/memcmp.c
index 15ca9b1d1..1b85af45d 100644
--- a/newlib/libc/machine/xscale/memcmp.c
+++ b/newlib/libc/machine/xscale/memcmp.c
@@ -8,99 +8,102 @@
#include "xscale.h"
int
-memcmp (const void *s1, const void *s2, size_t len)
+memcmp (const void * s1, const void * s2, size_t len)
{
int result;
asm (
#ifndef __OPTIMIZE_SIZE__
"
- cmp %2, #0x3
- bls 6f
- and r2, %0, #0x3
- and r3, %1, #0x3
- cmp r2, r3
- bne 6f
- mov lr, %0
- mov r4, %1
- cmp r2, #0x0
- beq 3f
- b 1f
-0:
- ldrb r2, [lr], #1 @ zero_extendqisi2
-" PRELOADSTR("lr") "
- ldrb r3, [r4], #1 @ zero_extendqisi2
-" PRELOADSTR("r4") "
- cmp r2, r3
- bne 5f
- tst lr, #0x3
- beq 3f
-1:
- sub %2, %2, #1
- cmn %2, #0x1
- bne 0b
- b 4f
+ cmp %2, #0x3 @ Is the length a multiple of four ?
+ bls 6f @ no = goto SLOW CHECK
+ and r2, %0, #0x3 @ get alignment of first pointer
+ and r3, %1, #0x3 @ get alignment of second pointer
+ cmp r2, r3 @ Do the two pointers share the same alignment ?
+ bne 6f @ no = goto SLOW CHECK
+ mov lr, %0 @ copy first pointer into LR
+ mov r4, %1 @ copy second pointer into R4
+ cmp r2, #0x0 @ Are we comparing word aligned pointers ?
+ beq 3f @ yes = goto START WORD CHECK LOOP
+ b 1f @ jump to LOOP TEST
+0: @ LOOP START
+ ldrb r2, [lr], #1 @ load byte from LR, post inc.
+" PRELOADSTR("lr") " @ preload
+ ldrb r3, [r4], #1 @ load byte from R4, post inc.
+" PRELOADSTR("r4") " @ preload
+ cmp r2, r3 @ are the two bytes the same ?
+ bne 5f @ no = goto EXIT
+ tst lr, #0x3 @ has the LR become word aligned ?
+ bne 1f @ no = skip the next test
+ cmp %2, #4 @ is the count >= 4 ?
+ bhs 3f @ yes = goto START WORD CHECK LOOP
+1: @ LOOP TEST
+ sub %2, %2, #1 @ decrement count by one
+ cmn %2, #0x1 @ has the count reached -1 ?
+ bne 0b @ no = loop back to LOOP START
+ b 4f @ goto PASS END
-0:
- cmp %2, #0x7
- bls 3f
- ldmia lr,{r2, r3}
- ldmia r4,{r5, r6}
- sub %2, %2, #0x4
- cmp r2, r5
- bne 1f
- sub %2, %2, #0x4
- add lr, lr, #0x4
- add r4, r4, #0x4
- cmp r3, r6
- beq 0b
-1:
- add %2, %2, #0x4
- sub %0, lr, #0x4
- sub %1, r4, #0x4
- b 6f
-3:
- cmp %2, #0x3
- bls 1f
- ldr r2, [lr], #4
- ldr r3, [r4], #4
- sub %2, %2, #4
- cmp r2, r3
- bne 1f
-0:
- cmp %2, #0x3
- bls 1f
- ldr r2, [lr], #4
-" PRELOADSTR("lr") "
- ldr r3, [r4], #4
-" PRELOADSTR("r4") "
- sub %2, %2, #4
- cmp r2, r3
- beq 0b
-1:
- sub %0, lr, #0x4
- sub %1, r4, #0x4
- add %2, %2, #4
-"
+0: @ ??
+ cmp %2, #0x7 @ Is the count a multiple of 8 ?
+ bls 3f @ no = goto ???
+ ldmia lr,{r2, r3} @ get two words from first pointer, post inc
+ ldmia r4,{r5, r6} @ get two words from second pointer, post inc
+ sub %2, %2, #0x4 @ decrement count by 4
+ cmp r2, r5 @ has the count reached ????
+ bne 1f @ no = goto
+ sub %2, %2, #0x4 @ decrement the count by 4
+ add lr, lr, #0x4 @ add 4 to first pointer
+ add r4, r4, #0x4 @ add 4 to second pointer
+ cmp r3, r6 @ ???
+ beq 0b @ goto ???
+1: @ ??
+ add %2, %2, #0x4 @ Add four to count
+ sub %0, lr, #0x4 @ decrement first pointer by 4
+ sub %1, r4, #0x4 @ decrement second pointer by 4
+ b 6f @ goto SLOW CHECK
+
+3: @ START WORD CHECK LOOP
+ cmp %2, #0x3 @ is the count <= 3 ?
+ bls 1f @ yes = goto CHECK BYTES BY HAND
+ ldr r2, [lr], #4 @ get word from LR, post inc
+ ldr r3, [r4], #4 @ get word from R4, post inc
+ sub %2, %2, #4 @ decrement count by 4
+ cmp r2, r3 @ are the two words the same ?
+ bne 1f @ no = goto CHECK WORD CONTENTS
+0: @ WORD CHECK LOOP
+ cmp %2, #0x3 @ is the count <= 3 ?
+ bls 1f @ yes = goto CHECK BYTES BY HAND
+ ldr r2, [lr], #4 @ load word from LR, post inc
+" PRELOADSTR("lr") " @ preload
+ ldr r3, [r4], #4 @ load word from R4, post inc
+" PRELOADSTR("r4") " @ preload
+ sub %2, %2, #4 @ decrement count by 4
+ cmp r2, r3 @ are the two words the same ?
+ beq 0b @ yes = goto WORD CHECK LOOP
+1: @ CHECK BYTES BY HAND
+ sub %0, lr, #0x4 @ move LR back a word and put into first pointer
+ sub %1, r4, #0x4 @ move R4 back a word and put into second pointer
+ add %2, %2, #4 @ increment the count by 4
+ @ fall through into SLOW CHECK"
#endif /* !__OPTIMIZE_SIZE__ */
"
-6:
- sub %2, %2, #1
- cmn %2, #0x1
- beq 4f
-0:
- ldrb r2, [%0], #1 @ zero_extendqisi2
-" PRELOADSTR("%0") "
- ldrb r3, [%1], #1 @ zero_extendqisi2
-" PRELOADSTR("%1") "
- cmp r2, r3
- bne 5f
- sub %2, %2, #1
- cmn %2, #0x1
- bne 0b
-4:
- mov r3, r2
-5:
- rsb %0, r3, r2"
+6: @ SLOW CHECK
+ sub %2, %2, #1 @ Decrement the count by one
+ cmn %2, #0x1 @ Has the count reached -1 ?
+ beq 4f @ Yes - we are finished, goto PASS END
+0: @ LOOP1
+ ldrb r2, [%0], #1 @ get byte from first pointer
+" PRELOADSTR("%0") " @ preload first pointer
+ ldrb r3, [%1], #1 @ get byte from second pointer
+" PRELOADSTR("%1") " @ preload second pointer
+ cmp r2, r3 @ compare the two loaded bytes
+ bne 5f @ if they are not equal goto EXIT
+ sub %2, %2, #1 @ decremented count by 1
+ cmn %2, #0x1 @ has the count reached -1 ?
+ bne 0b @ no = then go back to LOOP1
+4: @ PASS END
+ mov r3, r2 @ Default return value is 0
+5: @ EXIT
+ rsb %0, r3, r2 @ return difference between last two bytes loaded"
: "=r" (result), "=&r" (s2), "=&r" (len)
: "0" (s1), "1" (s2), "2" (len)
: "r2", "r3", "r4", "r5", "r6", "cc", "lr");