; ANY4.Z80, from ANYWHERE.ASM by Bridger Mitchell
; (ref. The Computer Journal, issue #33, pp.11,14-15)

; July 18, 1988 mods by Bruce Morgen to avoid lots of
; "LD (HL),nn" opcodes - at first it turned out to be
; a byte longer and a little slower!  Anyway, it's a
; brain-teaser to do it that way and I wound up with
; a combination of the two approaches that seems
; reasonably efficient and compact.  The register
; recovery feature is also sketched out - all primary
; registers except BC and IY can be passed to the
; program by PUSHing at ANYWHERE+3 and POPping at
; RDONE+3.  After the initial relocate-&-move run,
; of course, any register can be passed.

; July 15, 1988 mods by Bruce Morgen to to "pull" the
; relocated code down over the Where-Am-I and relocator
; routines as suggested by Bridger in the TCJ piece.

; July 14, 1988 mods by Bruce Morgen to allow easier
; creation of relocatable programs using MLOAD instead
; of a debugger/save sequence.  Sample procedure:

; ZAS ANY4 H or Z80ASM ANY4/H
; Assemble to a HEXfile
; (M80/L80 can't handle this correctly,
; use the M80 equate and the RELHEX
; utility if you must use M80.)
; MLOAD PROGNAME=PROGNAME.PRL,ANY4
; MLOAD v2.1 or later required

prl	equ	1		; Could also use SPR files, but
				; the DSEG handling could be
				; tricky - PRL preferred.

m80	equ	1		; Make this a 1 if using the
				; M80/RELHEX method

	 if	m80
	.z80
	aseg
	 endif

	org	100h		; Code is position-independent,
				; but MLOAD needs this anyway

anywhere:
	db	01h		; "LD BC" opcode
	ds	2		; PRL format code length here
				; (proper HEXfile won't overlay)
; Bridger's Where-Am-I routine
; We could save registers other than BC & IY here for later recovery
; e.g.:
;	push	hl
;	push	de

	ld	hl,0000		; Zero out HL
	push	hl		; Use it to clear IX & IY first
	pop	ix
	push	hl
	pop	iy
	add	ix,sp		; Store incoming SP in IX
	ld	a,(hl)		; Get byte at 0000h
	di			; Disable interrupt system
	ld	(hl),0c9h	; Poke a RET at 0000h
	rst	0		; "CALL" it
me:	ld	(hl),a		; Replace the original byte
	dec	sp		; Adjust SP
	dec	sp
	ei			; Interrupts OK again

	pop	hl		; Get ANYWHERE+ME from stack
	ld	de,anywhere-me	; Signed difference in DE
	add	hl,de		; HL pts to ANYWHERE

; Bridger's neat word-wide PRL/SPR relocator begins here,
; slightly modified to save the byte count and bitmap start

reloc:
	push	bc		; Byte count to stack - b/m
	push	hl		; ANYWHERE to stack
	exx
	pop	de		; Set DE' to relocation base of code
	pop	bc		; Set BC' to byte count - b/m
	 if	prl
	dec	d		; -100H for PRL version
	 endif
	exx
	inc	h		; Adjust HL to code start - b/m
	di
	ld	sp,hl
	dec	sp
	add	hl,bc
	ld	e,00000001b	; Init. rotation counter byte
	ex	de,hl		; Bitmap start to DE
	add	iy,de		; Get bitmap start in IY - b/m
	ex	de,hl		; Bitmap start back to HL

rloop:	ld	a,b		; Anything left to process?
	or	c
	jr	z,rdone		; Branch ahead if done
	dec	bc		; Decrement 16-bit byte counter
	rrc	e		; Rotate right, bit 7 = carry
	jr	nc,rsame	; If bit reset, same bitmap byte

	ld	d,(hl)		; Otherwise get byte from bitmap
	inc	hl		; Point to the next one
rsame:	rlc	d		; Rotate left, bit 0 = carry
	jr	nc,noof		; No carry means no relocation

	exx			; Go to alt. regs.
	pop	hl		; Get value in HL'
	add	hl,de		; Add in relocation base
	push	hl		; Put back relocated value
	exx			; Back to primary regs.

noof:	inc	sp		; Increment pointer to code
	jr	rloop		; Loop around

rdone:	ld	sp,ix		; Recover incoming SP
	ei

; Now overlay the bitmap area with our move & run routine - b/m
; We could recover saved registers other than BC & IY here
; e.g.:
;	pop	de
;	pop	hl

	exx			; Go to alt. registers
	push	iy		; Get bitmap start into HL'
	pop	hl
	 if	prl
	inc	d		; Adjust runtime origin if PRL
	 endif
	ld	(hl),0edh	; Move LDIR to (HL')
	inc	hl
	ld	(hl),0b0h
	inc	hl
	ld	(hl),0d9h	; EXX opcode next
	inc	hl
	ld	(hl),0c3h	; JP opcode next
	inc	hl
	ld	(hl),e		; Then ANYWHERE, as JP's operand
	inc	hl
	ld	(hl),d
	ld	h,d		; Copy LDIR dest. in DE' to HL'
	ld	l,e
	inc	h		; "Compute" LDIR source
	jp	(iy)		; Branch to MOVER & the program

; This code gets moved to (and executed in) the bitmap area
;
;mover:	ldir			; Move source to dest.
;	exx			; To primary regs.
;	jp "real"_anywhere	; Branch to the program

	end