**************************************

* Memory move

* NOTE: This routine properly moves overlapping areas of memory.
*       Uses fast move algorithm

* ENTRY: X=source data
*        Y=destination
*        D=count

* EXIT: all registers (except CC) preserved

 nam Move Memory
 ttl Assembler Library Module



 section .text

MEMMOVE:
 pshs d,x,y,u
 std -2,s test u
 beq exit zero count, exit
 tfr y,u use u for dest
 tfr d,y count in y
 cmpu 2,s compare dest. to source (x)
 beq exit same, no need to move
 bhi down u>x

up
 bitb #1 see if odd number to move
 beq up1
 lda ,x+ move odd byte
 sta ,u+
 leay -1,y could be only one
 beq exit

up1
 ldd ,x++ move 2 bytes 
 std ,u++
 leay -2,y count down
 bne up1
 bra exit

down
 leau d,u u=dest end (count in D)
 leax d,x x=source end

 bitb #1
 beq down2
 lda ,-x move odd byte
 sta ,-u
 leay -1,y could be only one to do
 beq exit

down2
 ldd ,--x get 2 bytes
 std ,--u move them
 leay -2,y count down
 bne down2

exit
 puls d,x,y,u,pc

 endsect