falso
/
z80
mirror of https://github.com/falsovsky/z80.git
1
0
Fork 0
Code Issues Releases Wiki Activity

Document

This commit is contained in:
Pedro de Oliveira 2014-08-14 05:55:30 +01:00
parent dc8797c576
commit 8d7e4dfcb0
1 changed files with 25 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

48
zx-brainfuck/main.asm
View File

@ -61,38 +61,40 @@ end_main
; -------------------------------------
; opcode comes in A
loopup_table
pop de
ld de, lookup_tbl_opcodes
ld hl, lookup_tbl_routines
ld c, $9
pop de ; Remove return address from stack
ld de, lookup_tbl_opcodes ; Start of opcodes_tbl in DE
ld hl, lookup_tbl_routines ; Start of routines_tbl in HL
ld c, $9 ; Number of valid opcodes + 1
loopup_table_loop
ld b, a
push bc
ld a, (de)
cp b
jr z, lookup_table_found
pop bc
ld a, b
inc de
ld b, a ; B = A (opcode to run)
push bc ; Push BC to the stack
; B = Opcode, C = counter
ld a, (de) ; Read item from opcodes_tbl
cp b ; Is it the same?
jr z, lookup_table_found ; Found it!
pop bc ; Get values from stack
ld a, b ; A = B (opcode to run)
inc de ; Next item in opcodes_tbl
inc hl
inc hl
dec c
jr z, lookup_table_default
jr loopup_table_loop
inc hl ; Next item in opcodes_routines
dec c ; C = C -1
jr z, lookup_table_default ; Is it 0? Non valid opcode
jr loopup_table_loop ; Repeat
lookup_table_found
pop bc
jr lookup_table_ret
lookup_table_default
ld de, continue
push de
ret
ld de, continue ; DE = address to "continue" label
push de ; Send it to the stack
ret ; Return to last item in the stack
lookup_table_ret
ld e, (hl)
inc hl
ld e, (hl) ; Save the address of the routine to
inc hl ; be RETurned in DE
ld d, (hl)
push de
ret
push de ; Send it to the stack
ret ; Return to last item in the stack
; -------------------------------------