Add a end to start version of memcpy, and a selectable

direction version of memcpy.

This can help with some subroutines/functions like
shftln, which need to copy data in a certain direction
depending on the condition.

1 files changed, 41 insertions, 4 deletions

diff --git a/programs/sub-suite/libc.s b/programs/sub-suite/libc.s
index 3de1094..b64eaf8 100644
--- a/programs/sub-suite/libc.s
+++ b/programs/sub-suite/libc.s
@@ -467,19 +467,56 @@ free:
 
 memcpy:
 	phb.q			; Preserve B.
-	xor b, b		; Reset B.
 	mov a, d		; Set the return value to the destination pointer.
-	cmp f, #0		; Is the size zero?
-	beq @end		; Yes, so we're done.
+	and f, f		; Is the size zero?
+	beq @end		; The size is zero, so we're done.
+	xor b, b		; Reset B.
 @loop:
 	mov (d+b), (s+b)	; Copy a byte from the source, into the destination.
 	inb			; Increment the counter.
 	cmp b, f		; Is the counter the same as the size?
-	bne @loop		; No, so keep looping.
+	bne @loop		; The size is non-zero, so keep looping.
+@end:
+	plb.q			; Restore B.
+	rts			; End of memcpy.
+
+; memcpy_back: memory to memory copy from end to start.
+; Input: D = Destination pointer. S = Source pointer. F = Number of bytes to copy.
+; Output: A = Destination pointer.
+; Caller preserved registers: D, S, F.
+; Callee preserved registers: B.
+
+memcpy_back:
+	phb.q			; Preserve B.
+	mov a, d		; Set the return value to the destination pointer.
+	mov b, f		; Copy the size into B.
+@loop:
+	cpb #0			; Is the size zero?
+	beq @end		; Yes, so we're done.
+	deb			; No, so decrement the size.
+	mov (d+b), (s+b)	; Copy a byte from the source, into the destination.
+	bra @loop		; Keep looping.
 @end:
 	plb.q			; Restore B.
 	rts			; End of memcpy.
 
+; memcpy_dir: memory to memory copy with selectable direction.
+; Input: D = Destination pointer. S = Source pointer. F = Number of bytes to copy.
+; C = direction flag, 0 = start to end, 1 = end to start.
+; Output: A = Destination pointer.
+; Caller preserved registers: D, S, F, C.
+; Callee preserved registers: none.
+
+memcpy_dir:
+	and c, c		; Is the direction flag set?
+	bne @back		; Yes, so copy from end to start.
+@forward:
+	jsr memcpy		; Copy from start to end.
+	bra @end		; We are done.
+@back:
+	jsr memcpy_back		; Copy from end to start.
+@end:
+	rts			; End of memcpy_dir.
 
 ; memset: Set memory to some value.
 ; Input: D = Destination pointer. S = Constant value. F = Number of bytes to set.