subttl  Macro definitions

; In segment 'segzero' set $ to the next multiple of 'n'.
align	  macro   n,segzero
	  org	$ - (($-segzero) MOD n) + n
	  endm

; Issue a DOS function request (int 21h) after
; setting up registers ax,bx,cx,dx,ds,es.
; Registers not specified are not affected by the macro,
; code to move a reg to itself is skipped, and
; moves between DS and ES are handled.
dos_fr	  macro   rax,rbx,rcx,rdx,rds,res
	  ifnb	  <rax> 	   ;;ax
	  ifidn   <rax>,<ax>
	  else
	  mov	  ax,rax
	  endif
	  endif
	  ifnb	  <rbx> 	   ;;bx
	  ifidn   <rbx>,<bx>
	  else
	  mov	  bx,rbx
	  endif
	  endif
	  ifnb	  <rcx> 	   ;;cx
	  ifidn   <rcx>,<cx>
	  else
	  mov	  cx,rcx
	  endif
	  endif
	  ifnb	  <rdx> 	   ;;dx
	  ifidn   <rdx>,<dx>
	  else
	  mov	  dx,rdx
	  endif
	  endif
	  ifnb	  <res> 	   ;;es
	  ifidn   <res>,<ds>
	  push	  ds
	  pop	  es
	  else
	  ifidn   <res>,<es>
	  else
	  mov	  es,res
	  endif
	  endif
	  endif
	  ifnb	  <rds> 	   ;;ds
	  ifidn   <rds>,<es>
	  push	  es
	  pop	  ds
	  else
	  ifidn   <rds>,<ds>
	  else
	  mov	  ds,rds
	  endif
	  endif
	  endif
	  int	  21h
	  endm

; Given the value of "active_exe", put into BX the corresponding byte offset
; into various tables.	If table="itself", just load BX.
;
; Note: The calculated byte offset must fit into BL because we use BH for
;	scratch.  We don't affect any other register this way.  If the
;	number of entries allowed in the tables is enlarged so that we
;	could overflow into BH, this macro will need changing.	Changing
;	a table's format will obviously affect this macro too.
load_index macro  table
	  mov	  bx,active_exe
	  ifdif   <itself>,<table>
	  xor	  bh,bh
	  endif
	  ifidn   <load_table>,<table>
	  shl	  bx,1		   ;; 2 bytes/entry
	  endif
	  ifidn   <fb_table>,<table>
	  shl	  bx,1		   ;; 4
	  shl	  bx,1
	  endif
	  ifidn   <pb_table>,<table>
	  shl	  bx,1		   ;; 4
	  shl	  bx,1
	  endif
	  ifidn   <state_table>,<table>
	  mov	  bh,bl
	  shl	  bx,1		   ;;shift BH and BL simultaneously
	  shl	  bl,1
	  shl	  bl,1
	  add	  bl,bh 	   ;; 10
	  xor	  bh,bh
	  endif
	  ifidn   <status_table>,<table>
	  shl	  bx,1		   ;; 2
	  endif
	  endm

; *** All registers on entry except CS,IP belong to the child.		***
; *** On exit, all registers except CS,IP,DS still belong to the child. ***
; This routine captures all the child's registers' values (except CS:IP,
; which is located on the stack at the saved SS:SP).
; DS is changed to PCS's data segment.
save_state macro
	  push	  ds		   ;pushes are in child's data segment
	  push	  ax
	  mov	  ax,data
	  mov	  ds,ax 	   ;DS points to PCS's data segment
	  pop	  ax		   ;get back ax
	  mov	  save_ax,ax
	  mov	  save_bx,bx
	  mov	  save_cx,cx
	  mov	  save_dx,dx
	  mov	  save_si,si
	  mov	  save_di,di
	  pop	  ax		   ;get back ds (stack now same as on entry)
	  mov	  save_ds,ax
	  mov	  save_es,es
	  mov	  save_ss,ss
	  mov	  save_sp,sp
	  mov	  save_bp,bp
	  endm

; Save the parent's (i.e. PCS's) segment and pointer registers.
save_parent macro
	  mov	  pcs_state.st_es,es	;save our state
	  mov	  pcs_state.st_ss,ss
	  mov	  pcs_state.st_sp,sp
	  mov	  pcs_state.st_bp,bp
	  mov	  pcs_state.st_ds,ds
	  endm

; Restore the parent's segment and pointer registers.
restore_parent macro
	  mov	  bx,offset pcs_state	;restore parent's state
	  cli
	  mov	  es,[bx].st_es
	  mov	  ss,[bx].st_ss
	  mov	  sp,[bx].st_sp
	  mov	  bp,[bx].st_bp
;;	  mov	  ds,[bx].st_ds    ;save_state made DS active already
	  sti
	  endm

; Save off our registers and restore child's, then resume child.
call_child macro  x
	  save_parent
	  load_index state_table
	  lea	  bx,state_table[bx]
	  cli				; restore child's state
	  mov	  es,[bx].st_es
	  mov	  ss,[bx].st_ss
	  mov	  sp,[bx].st_sp
	  mov	  bp,[bx].st_bp
	  mov	  ds,[bx].st_ds
	  sti
xlidbg&x  label   byte
	  nop				;;this gets replaced with INT 3 for debug
	  nop
	  db	  0CBh			;resume child via far return
	  endm

; Save off child's registers and restore ours, then continue.
resume_parent macro
	  save_state			;save child's registers in global area
	  restore_parent
	  load_index state_table
	  lea	  bx,state_table[bx]
	  mov	  ax,save_ds		;save child's regs in child-local area
	  mov	  [bx].st_ds,ax
	  mov	  ax,save_es
	  mov	  [bx].st_es,ax
	  mov	  ax,save_ss
	  mov	  [bx].st_ss,ax
	  mov	  ax,save_sp
	  mov	  [bx].st_sp,ax
	  mov	  ax,save_bp
	  mov	  [bx].st_bp,ax
	  endm