HP UX Developer Tools manual Copying a String, 132

Programming Examples

2. Copying a String

2. Copying a String

This example contains a section of assembly code that moves a byte string of arbitrary length to an arbitrary byte address.

;The routine reflect copies bytes from the source location

;to the destination location.

;

;The first parameter is the source address and the second

;parameter is the destination address.

;

;The third parameter is the number of bytes to copy.

;For performance, larger chunks of bytes are handled differently.

.CODE

.EXPORT reflect,ENTRY

reflect
.PROC
.CALLINFO	ENTRY_GR=6,SAVE_RP
.ENTER
COMB,=,N	%arg2,%r0,fallout	; done, count is zero
COMB,<,N	%arg2,%r0,choke	; caller error, neg count
OR	%arg0,%arg1,%r6	; source and dest
OR	%r6,%arg2,%r6	; count
EXTRU,=	%r6,31,2,%r0	; 2 low order bits = 0?
B,N	onebyte	; yes, skip this branch
ADDIBT,<,N	-16,%arg2,chekchunk	; no, skip chunkify if count<0
chunkify
LDWM	16(%arg0),%r6	; word 1- > temp1
		; point ahead 4 words in source
LDW	-12(%arg0),%r5	; place mark 3 wds back- >temp2
LDW	-8(%arg0),%r4	; place mark 2 wds back- >temp3
LDW	-4(%arg0),%r3	; place mark 1 wds back- >temp4
STW	%r5,4(%arg1)	; dest wd 2 <-temp2
STWM	%r6,16(%arg1)	; dest wd 1 <-temp1
		; point ahead 4 words in dest
STW	%r4,-8(%arg1)	; dest wd 3 <-temp3
ADDIBF,<	-16,%arg2,chunkify	; loop if count > 0
STW	%r3,-4(%arg1)	; dest wd 2 <-temp1
chekchunk
ADDIBT,<	12,%arg2,exeunt	; go if count < -12
COPY	%r0,%ret0	; clear rtnval
subchunk
LDWS,MA	4(%arg0),%r6	; word- >temp1
		; point ahead 4 bytes in source
ADDIBF,<	-4,%arg2,subchunk	; go if count<4
STWS,MA	%r6,4(%arg1)	; dest< -temp1
		; point ahead 4 bytes in dest

132 Chapter 7