; Internal library routines - always included by the compiler ; Generic machine independent 6502 code. orig_stackpointer .byte 0 ; stores the Stack pointer register at program start read_byte_from_address_on_stack .proc ; -- read the byte from the memory address on the top of the stack, return in A (stack remains unchanged) lda P8ESTACK_LO+1,x ldy P8ESTACK_HI+1,x sta P8ZP_SCRATCH_W2 sty P8ZP_SCRATCH_W2+1 ldy #0 lda (P8ZP_SCRATCH_W2),y rts .pend write_byte_to_address_on_stack .proc ; -- write the byte in A to the memory address on the top of the stack (stack remains unchanged) ldy P8ESTACK_LO+1,x sty P8ZP_SCRATCH_W2 ldy P8ESTACK_HI+1,x sty P8ZP_SCRATCH_W2+1 ldy #0 sta (P8ZP_SCRATCH_W2),y rts .pend neg_b .proc lda #0 sec sbc P8ESTACK_LO+1,x sta P8ESTACK_LO+1,x rts .pend neg_w .proc sec lda #0 sbc P8ESTACK_LO+1,x sta P8ESTACK_LO+1,x lda #0 sbc P8ESTACK_HI+1,x sta P8ESTACK_HI+1,x rts .pend inv_word .proc lda P8ESTACK_LO+1,x eor #255 sta P8ESTACK_LO+1,x lda P8ESTACK_HI+1,x eor #255 sta P8ESTACK_HI+1,x rts .pend bitand_b .proc ; -- bitwise and (of 2 bytes) lda P8ESTACK_LO+2,x and P8ESTACK_LO+1,x inx sta P8ESTACK_LO+1,x rts .pend bitor_b .proc ; -- bitwise or (of 2 bytes) lda P8ESTACK_LO+2,x ora P8ESTACK_LO+1,x inx sta P8ESTACK_LO+1,x rts .pend bitxor_b .proc ; -- bitwise xor (of 2 bytes) lda P8ESTACK_LO+2,x eor P8ESTACK_LO+1,x inx sta P8ESTACK_LO+1,x rts .pend bitand_w .proc ; -- bitwise and (of 2 words) lda P8ESTACK_LO+2,x and P8ESTACK_LO+1,x sta P8ESTACK_LO+2,x lda P8ESTACK_HI+2,x and P8ESTACK_HI+1,x sta P8ESTACK_HI+2,x inx rts .pend bitor_w .proc ; -- bitwise or (of 2 words) lda P8ESTACK_LO+2,x ora P8ESTACK_LO+1,x sta P8ESTACK_LO+2,x lda P8ESTACK_HI+2,x ora P8ESTACK_HI+1,x sta P8ESTACK_HI+2,x inx rts .pend bitxor_w .proc ; -- bitwise xor (of 2 bytes) lda P8ESTACK_LO+2,x eor P8ESTACK_LO+1,x sta P8ESTACK_LO+2,x lda P8ESTACK_HI+2,x eor P8ESTACK_HI+1,x sta P8ESTACK_HI+2,x inx rts .pend add_w .proc ; -- push word+word / uword+uword inx clc lda P8ESTACK_LO,x adc P8ESTACK_LO+1,x sta P8ESTACK_LO+1,x lda P8ESTACK_HI,x adc P8ESTACK_HI+1,x sta P8ESTACK_HI+1,x rts .pend sub_w .proc ; -- push word-word inx sec lda P8ESTACK_LO+1,x sbc P8ESTACK_LO,x sta P8ESTACK_LO+1,x lda P8ESTACK_HI+1,x sbc P8ESTACK_HI,x sta P8ESTACK_HI+1,x rts .pend mul_byte .proc ; -- b*b->b (signed and unsigned) inx lda P8ESTACK_LO,x ldy P8ESTACK_LO+1,x jsr math.multiply_bytes sta P8ESTACK_LO+1,x rts .pend mul_word .proc inx lda P8ESTACK_LO,x sta P8ZP_SCRATCH_W1 lda P8ESTACK_HI,x sta P8ZP_SCRATCH_W1+1 lda P8ESTACK_LO+1,x ldy P8ESTACK_HI+1,x jsr math.multiply_words sta P8ESTACK_LO+1,x tya sta P8ESTACK_HI+1,x rts .pend idiv_b .proc ; signed division: use unsigned division and fix sign of result afterwards inx lda P8ESTACK_LO,x eor P8ESTACK_LO+1,x php ; save sign of result lda P8ESTACK_LO,x bpl + eor #$ff sec adc #0 ; make num1 positive + tay inx lda P8ESTACK_LO,x bpl + eor #$ff sec adc #0 ; make num2 positive + jsr math.divmod_ub_asm sta _remainder tya plp ; get sign of result bpl + eor #$ff sec adc #0 ; negate result + sta P8ESTACK_LO,x dex rts _remainder .byte 0 .pend idiv_ub .proc inx ldy P8ESTACK_LO,x lda P8ESTACK_LO+1,x jsr math.divmod_ub_asm tya sta P8ESTACK_LO+1,x rts .pend idiv_w .proc ; signed division: use unsigned division and fix sign of result afterwards lda P8ESTACK_HI+2,x eor P8ESTACK_HI+1,x php ; save sign of result lda P8ESTACK_HI+1,x bpl + jsr neg_w ; make value positive + inx lda P8ESTACK_HI+1,x bpl + jsr neg_w ; make value positive + lda P8ESTACK_LO+1,x sta P8ZP_SCRATCH_W1 lda P8ESTACK_HI+1,x sta P8ZP_SCRATCH_W1+1 lda P8ESTACK_LO,x ldy P8ESTACK_HI,x jsr math.divmod_uw_asm sta P8ESTACK_LO+1,x tya sta P8ESTACK_HI+1,x plp bpl + jmp neg_w ; negate result + rts .pend idiv_uw .proc inx lda P8ESTACK_LO+1,x sta P8ZP_SCRATCH_W1 lda P8ESTACK_HI+1,x sta P8ZP_SCRATCH_W1+1 lda P8ESTACK_LO,x ldy P8ESTACK_HI,x jsr math.divmod_uw_asm sta P8ESTACK_LO+1,x tya sta P8ESTACK_HI+1,x rts .pend remainder_ub .proc inx ldy P8ESTACK_LO,x ; right operand lda P8ESTACK_LO+1,x ; left operand jsr math.divmod_ub_asm sta P8ESTACK_LO+1,x rts .pend remainder_uw .proc inx lda P8ESTACK_LO+1,x sta P8ZP_SCRATCH_W1 lda P8ESTACK_HI+1,x sta P8ZP_SCRATCH_W1+1 lda P8ESTACK_LO,x ldy P8ESTACK_HI,x jsr math.divmod_uw_asm lda P8ZP_SCRATCH_W2 sta P8ESTACK_LO+1,x lda P8ZP_SCRATCH_W2+1 sta P8ESTACK_HI+1,x rts .pend equal_w .proc ; -- are the two words on the stack identical? lda P8ESTACK_LO+1,x cmp P8ESTACK_LO+2,x bne equal_b._equal_b_false lda P8ESTACK_HI+1,x cmp P8ESTACK_HI+2,x bne equal_b._equal_b_false beq equal_b._equal_b_true .pend notequal_b .proc ; -- are the two bytes on the stack different? lda P8ESTACK_LO+1,x cmp P8ESTACK_LO+2,x beq equal_b._equal_b_false bne equal_b._equal_b_true .pend notequal_w .proc ; -- are the two words on the stack different? lda P8ESTACK_HI+1,x cmp P8ESTACK_HI+2,x beq notequal_b bne equal_b._equal_b_true .pend less_ub .proc lda P8ESTACK_LO+2,x cmp P8ESTACK_LO+1,x bcc equal_b._equal_b_true bcs equal_b._equal_b_false .pend less_b .proc ; see http://www.6502.org/tutorials/compare_beyond.html lda P8ESTACK_LO+2,x sec sbc P8ESTACK_LO+1,x bvc + eor #$80 + bmi equal_b._equal_b_true bpl equal_b._equal_b_false .pend reg_less_uw .proc ; AY < P8ZP_SCRATCH_W2? cpy P8ZP_SCRATCH_W2+1 bcc _true bne _false cmp P8ZP_SCRATCH_W2 bcc _true _false lda #0 rts _true lda #1 rts .pend less_uw .proc lda P8ESTACK_HI+2,x cmp P8ESTACK_HI+1,x bcc equal_b._equal_b_true bne equal_b._equal_b_false lda P8ESTACK_LO+2,x cmp P8ESTACK_LO+1,x bcc equal_b._equal_b_true bcs equal_b._equal_b_false .pend reg_less_w .proc ; -- AY < P8ZP_SCRATCH_W2? cmp P8ZP_SCRATCH_W2 tya sbc P8ZP_SCRATCH_W2+1 bvc + eor #$80 + bmi _true lda #0 rts _true lda #1 rts .pend less_w .proc lda P8ESTACK_LO+2,x cmp P8ESTACK_LO+1,x lda P8ESTACK_HI+2,x sbc P8ESTACK_HI+1,x bvc + eor #$80 + bmi equal_b._equal_b_true bpl equal_b._equal_b_false .pend equal_b .proc ; -- are the two bytes on the stack identical? lda P8ESTACK_LO+2,x cmp P8ESTACK_LO+1,x bne _equal_b_false _equal_b_true lda #1 _equal_b_store inx sta P8ESTACK_LO+1,x rts _equal_b_false lda #0 beq _equal_b_store .pend lesseq_ub .proc lda P8ESTACK_LO+1,x cmp P8ESTACK_LO+2,x bcs equal_b._equal_b_true bcc equal_b._equal_b_false .pend lesseq_b .proc ; see http://www.6502.org/tutorials/compare_beyond.html lda P8ESTACK_LO+2,x clc sbc P8ESTACK_LO+1,x bvc + eor #$80 + bmi equal_b._equal_b_true bpl equal_b._equal_b_false .pend reg_lesseq_uw .proc ; AY <= P8ZP_SCRATCH_W2? cpy P8ZP_SCRATCH_W2+1 beq + bcc _true lda #0 rts + cmp P8ZP_SCRATCH_W2 bcc _true beq _true lda #0 rts _true lda #1 rts .pend lesseq_uw .proc lda P8ESTACK_HI+1,x cmp P8ESTACK_HI+2,x bcc equal_b._equal_b_false bne equal_b._equal_b_true lda P8ESTACK_LO+1,x cmp P8ESTACK_LO+2,x bcs equal_b._equal_b_true bcc equal_b._equal_b_false .pend reg_lesseq_w .proc ; -- P8ZP_SCRATCH_W2 <= AY ? (note: order different from other routines) cmp P8ZP_SCRATCH_W2 tya sbc P8ZP_SCRATCH_W2+1 bvc + eor #$80 + bpl + lda #0 rts + lda #1 rts .pend lesseq_w .proc lda P8ESTACK_LO+1,x cmp P8ESTACK_LO+2,x lda P8ESTACK_HI+1,x sbc P8ESTACK_HI+2,x bvc + eor #$80 + bpl equal_b._equal_b_true bmi equal_b._equal_b_false .pend greater_ub .proc lda P8ESTACK_LO+2,x cmp P8ESTACK_LO+1,x beq equal_b._equal_b_false bcs equal_b._equal_b_true bcc equal_b._equal_b_false .pend greater_b .proc ; see http://www.6502.org/tutorials/compare_beyond.html lda P8ESTACK_LO+2,x clc sbc P8ESTACK_LO+1,x bvc + eor #$80 + bpl equal_b._equal_b_true bmi equal_b._equal_b_false .pend greater_uw .proc lda P8ESTACK_HI+1,x cmp P8ESTACK_HI+2,x bcc equal_b._equal_b_true bne equal_b._equal_b_false lda P8ESTACK_LO+1,x cmp P8ESTACK_LO+2,x bcc equal_b._equal_b_true bcs equal_b._equal_b_false .pend greater_w .proc lda P8ESTACK_LO+1,x cmp P8ESTACK_LO+2,x lda P8ESTACK_HI+1,x sbc P8ESTACK_HI+2,x bvc + eor #$80 + bmi equal_b._equal_b_true bpl equal_b._equal_b_false .pend greatereq_ub .proc lda P8ESTACK_LO+2,x cmp P8ESTACK_LO+1,x bcs equal_b._equal_b_true bcc equal_b._equal_b_false .pend greatereq_b .proc ; see http://www.6502.org/tutorials/compare_beyond.html lda P8ESTACK_LO+2,x sec sbc P8ESTACK_LO+1,x bvc + eor #$80 + bpl equal_b._equal_b_true bmi equal_b._equal_b_false .pend greatereq_uw .proc lda P8ESTACK_HI+2,x cmp P8ESTACK_HI+1,x bcc equal_b._equal_b_false bne equal_b._equal_b_true lda P8ESTACK_LO+2,x cmp P8ESTACK_LO+1,x bcs equal_b._equal_b_true bcc equal_b._equal_b_false .pend greatereq_w .proc lda P8ESTACK_LO+2,x cmp P8ESTACK_LO+1,x lda P8ESTACK_HI+2,x sbc P8ESTACK_HI+1,x bvc + eor #$80 + bmi equal_b._equal_b_false bpl equal_b._equal_b_true .pend shiftleft_b .proc inx ldy P8ESTACK_LO,x bne + rts + lda P8ESTACK_LO+1,x - asl a dey bne - sta P8ESTACK_LO+1,x rts .pend shiftright_b .proc inx ldy P8ESTACK_LO,x bne + rts + lda P8ESTACK_LO+1,x - lsr a dey bne - sta P8ESTACK_LO+1,x rts .pend equalzero_b .proc lda P8ESTACK_LO+1,x beq _true bne _false _true lda #1 sta P8ESTACK_LO+1,x rts _false lda #0 sta P8ESTACK_LO+1,x rts .pend equalzero_w .proc lda P8ESTACK_LO+1,x ora P8ESTACK_HI+1,x beq equalzero_b._true bne equalzero_b._false .pend notequalzero_b .proc lda P8ESTACK_LO+1,x beq equalzero_b._false bne equalzero_b._true .pend notequalzero_w .proc lda P8ESTACK_LO+1,x ora P8ESTACK_HI+1,x beq equalzero_b._false bne equalzero_b._true .pend lesszero_b .proc lda P8ESTACK_LO+1,x bmi equalzero_b._true jmp equalzero_b._false .pend lesszero_w .proc lda P8ESTACK_HI+1,x bmi equalzero_b._true jmp equalzero_b._false .pend greaterzero_ub .proc lda P8ESTACK_LO+1,x bne equalzero_b._true beq equalzero_b._false .pend greaterzero_sb .proc lda P8ESTACK_LO+1,x beq equalzero_b._false bpl equalzero_b._true bmi equalzero_b._false .pend greaterzero_uw .proc lda P8ESTACK_LO+1,x ora P8ESTACK_HI+1,x bne equalzero_b._true beq equalzero_b._false .pend greaterzero_sw .proc lda P8ESTACK_HI+1,x bmi equalzero_b._false ora P8ESTACK_LO+1,x beq equalzero_b._false bne equalzero_b._true .pend lessequalzero_sb .proc lda P8ESTACK_LO+1,x bmi equalzero_b._true beq equalzero_b._true bne equalzero_b._false .pend lessequalzero_sw .proc lda P8ESTACK_HI+1,x bmi equalzero_b._true ora P8ESTACK_LO+1,x beq equalzero_b._true bne equalzero_b._false .pend greaterequalzero_sb .proc lda P8ESTACK_LO+1,x bpl equalzero_b._true bmi equalzero_b._false .pend greaterequalzero_sw .proc lda P8ESTACK_HI+1,x bpl equalzero_b._true bmi equalzero_b._false .pend memcopy16_up .proc ; -- copy memory UP from (P8ZP_SCRATCH_W1) to (P8ZP_SCRATCH_W2) of length X/Y (16-bit, X=lo, Y=hi) ; clobbers register A,X,Y source = P8ZP_SCRATCH_W1 dest = P8ZP_SCRATCH_W2 length = P8ZP_SCRATCH_B1 ; (and SCRATCH_ZPREG) stx length sty length+1 ldx length ; move low byte of length into X bne + ; jump to start if X > 0 dec length ; subtract 1 from length + ldy #0 ; set Y to 0 - lda (source),y ; set A to whatever (source) points to offset by Y sta (dest),y ; move A to location pointed to by (dest) offset by Y iny ; increment Y bne + ; if Y<>0 then (rolled over) then still moving bytes inc source+1 ; increment hi byte of source inc dest+1 ; increment hi byte of dest + dex ; decrement X (lo byte counter) bne - ; if X<>0 then move another byte dec length ; we've moved 255 bytes, dec length bpl - ; if length is still positive go back and move more rts ; done .pend memset .proc ; -- fill memory from (P8ZP_SCRATCH_W1), length XY, with value in A. ; clobbers X, Y stx P8ZP_SCRATCH_B1 sty _save_reg ldy #0 ldx _save_reg beq _lastpage _fullpage sta (P8ZP_SCRATCH_W1),y iny bne _fullpage inc P8ZP_SCRATCH_W1+1 ; next page dex bne _fullpage _lastpage ldy P8ZP_SCRATCH_B1 beq + - dey sta (P8ZP_SCRATCH_W1),y bne - + rts _save_reg .byte 0 .pend memsetw .proc ; -- fill memory from (P8ZP_SCRATCH_W1) number of words in P8ZP_SCRATCH_W2, with word value in AY. ; clobbers A, X, Y sta _mod1+1 ; self-modify sty _mod1b+1 ; self-modify sta _mod2+1 ; self-modify sty _mod2b+1 ; self-modify ldx P8ZP_SCRATCH_W1 stx P8ZP_SCRATCH_B1 ldx P8ZP_SCRATCH_W1+1 inx stx P8ZP_SCRATCH_REG ; second page ldy #0 ldx P8ZP_SCRATCH_W2+1 beq _lastpage _fullpage _mod1 lda #0 ; self-modified sta (P8ZP_SCRATCH_W1),y ; first page sta (P8ZP_SCRATCH_B1),y ; second page iny _mod1b lda #0 ; self-modified sta (P8ZP_SCRATCH_W1),y ; first page sta (P8ZP_SCRATCH_B1),y ; second page iny bne _fullpage inc P8ZP_SCRATCH_W1+1 ; next page pair inc P8ZP_SCRATCH_W1+1 ; next page pair inc P8ZP_SCRATCH_B1+1 ; next page pair inc P8ZP_SCRATCH_B1+1 ; next page pair dex bne _fullpage _lastpage ldx P8ZP_SCRATCH_W2 beq _done ldy #0 - _mod2 lda #0 ; self-modified sta (P8ZP_SCRATCH_W1), y inc P8ZP_SCRATCH_W1 bne _mod2b inc P8ZP_SCRATCH_W1+1 _mod2b lda #0 ; self-modified sta (P8ZP_SCRATCH_W1), y inc P8ZP_SCRATCH_W1 bne + inc P8ZP_SCRATCH_W1+1 + dex bne - _done rts .pend ror2_mem_ub .proc ; -- in-place 8-bit ror of byte at memory location in AY sta P8ZP_SCRATCH_W1 sty P8ZP_SCRATCH_W1+1 ldy #0 lda (P8ZP_SCRATCH_W1),y lsr a bcc + ora #$80 + sta (P8ZP_SCRATCH_W1),y rts .pend rol2_mem_ub .proc ; -- in-place 8-bit rol of byte at memory location in AY sta P8ZP_SCRATCH_W1 sty P8ZP_SCRATCH_W1+1 ldy #0 lda (P8ZP_SCRATCH_W1),y cmp #$80 rol a sta (P8ZP_SCRATCH_W1),y rts .pend rol_array_ub .proc ; -- rol a ubyte in an array lda _arg_target ldy _arg_target+1 sta P8ZP_SCRATCH_W1 sty P8ZP_SCRATCH_W1+1 ldy _arg_index lda (P8ZP_SCRATCH_W1),y rol a sta (P8ZP_SCRATCH_W1),y rts _arg_target .word 0 _arg_index .byte 0 .pend ror_array_ub .proc ; -- ror a ubyte in an array lda _arg_target ldy _arg_target+1 sta P8ZP_SCRATCH_W1 sty P8ZP_SCRATCH_W1+1 ldy _arg_index lda (P8ZP_SCRATCH_W1),y ror a sta (P8ZP_SCRATCH_W1),y rts _arg_target .word 0 _arg_index .byte 0 .pend ror2_array_ub .proc ; -- ror2 (8-bit ror) a ubyte in an array lda _arg_target ldy _arg_target+1 sta P8ZP_SCRATCH_W1 sty P8ZP_SCRATCH_W1+1 ldy _arg_index lda (P8ZP_SCRATCH_W1),y lsr a bcc + ora #$80 + sta (P8ZP_SCRATCH_W1),y rts _arg_target .word 0 _arg_index .byte 0 .pend rol2_array_ub .proc ; -- rol2 (8-bit rol) a ubyte in an array lda _arg_target ldy _arg_target+1 sta P8ZP_SCRATCH_W1 sty P8ZP_SCRATCH_W1+1 ldy _arg_index lda (P8ZP_SCRATCH_W1),y cmp #$80 rol a sta (P8ZP_SCRATCH_W1),y rts _arg_target .word 0 _arg_index .byte 0 .pend ror_array_uw .proc ; -- ror a uword in an array php lda _arg_target ldy _arg_target+1 sta P8ZP_SCRATCH_W1 sty P8ZP_SCRATCH_W1+1 lda _arg_index asl a tay iny lda (P8ZP_SCRATCH_W1),y plp ror a sta (P8ZP_SCRATCH_W1),y dey lda (P8ZP_SCRATCH_W1),y ror a sta (P8ZP_SCRATCH_W1),y rts _arg_target .word 0 _arg_index .byte 0 .pend rol_array_uw .proc ; -- rol a uword in an array php lda _arg_target ldy _arg_target+1 sta P8ZP_SCRATCH_W1 sty P8ZP_SCRATCH_W1+1 lda _arg_index asl a tay lda (P8ZP_SCRATCH_W1),y plp rol a sta (P8ZP_SCRATCH_W1),y iny lda (P8ZP_SCRATCH_W1),y rol a sta (P8ZP_SCRATCH_W1),y rts _arg_target .word 0 _arg_index .byte 0 .pend rol2_array_uw .proc ; -- rol2 (16-bit rol) a uword in an array lda _arg_target ldy _arg_target+1 sta P8ZP_SCRATCH_W1 sty P8ZP_SCRATCH_W1+1 lda _arg_index asl a tay lda (P8ZP_SCRATCH_W1),y asl a sta (P8ZP_SCRATCH_W1),y iny lda (P8ZP_SCRATCH_W1),y rol a sta (P8ZP_SCRATCH_W1),y bcc + dey lda (P8ZP_SCRATCH_W1),y adc #0 sta (P8ZP_SCRATCH_W1),y + rts _arg_target .word 0 _arg_index .byte 0 .pend ror2_array_uw .proc ; -- ror2 (16-bit ror) a uword in an array lda _arg_target ldy _arg_target+1 sta P8ZP_SCRATCH_W1 sty P8ZP_SCRATCH_W1+1 lda _arg_index asl a tay iny lda (P8ZP_SCRATCH_W1),y lsr a sta (P8ZP_SCRATCH_W1),y dey lda (P8ZP_SCRATCH_W1),y ror a sta (P8ZP_SCRATCH_W1),y bcc + iny lda (P8ZP_SCRATCH_W1),y ora #$80 sta (P8ZP_SCRATCH_W1),y + rts _arg_target .word 0 _arg_index .byte 0 .pend strcpy .proc ; copy a string (must be 0-terminated) from A/Y to (P8ZP_SCRATCH_W1) ; it is assumed the target string is large enough. ; returns the length of the string that was copied in Y. sta P8ZP_SCRATCH_W2 sty P8ZP_SCRATCH_W2+1 ldy #$ff - iny lda (P8ZP_SCRATCH_W2),y sta (P8ZP_SCRATCH_W1),y bne - rts .pend strcmp_expression .proc ; -- compare strings, result in A lda _arg_s2 ldy _arg_s2+1 sta P8ZP_SCRATCH_W2 sty P8ZP_SCRATCH_W2+1 lda _arg_s1 ldy _arg_s1+1 jmp strcmp_mem _arg_s1 .word 0 _arg_s2 .word 0 .pend strcmp_stack .proc ; -- compare strings, both on stack. ; Returns -1,0,1 in A, depeding on the ordering. Clobbers Y. inx lda P8ESTACK_LO,x ldy P8ESTACK_HI,x sta P8ZP_SCRATCH_W2 sty P8ZP_SCRATCH_W2+1 inx lda P8ESTACK_LO,x ldy P8ESTACK_HI,x jmp strcmp_mem .pend strcmp_mem .proc ; -- compares strings in s1 (AY) and s2 (P8ZP_SCRATCH_W2). ; Returns -1,0,1 in A, depeding on the ordering. Clobbers Y. sta P8ZP_SCRATCH_W1 sty P8ZP_SCRATCH_W1+1 ldy #0 _loop lda (P8ZP_SCRATCH_W1),y bne + lda (P8ZP_SCRATCH_W2),y bne _return_minusone beq _return + cmp (P8ZP_SCRATCH_W2),y bcc _return_minusone bne _return_one inc P8ZP_SCRATCH_W1 bne + inc P8ZP_SCRATCH_W1+1 + inc P8ZP_SCRATCH_W2 bne _loop inc P8ZP_SCRATCH_W2+1 bne _loop _return_one lda #1 _return rts _return_minusone lda #-1 rts .pend sign_extend_stack_byte .proc ; -- sign extend the (signed) byte on the stack to full 16 bits lda P8ESTACK_LO+1,x ora #$7f bmi + lda #0 + sta P8ESTACK_HI+1,x rts .pend strlen .proc ; -- returns the number of bytes in the string in AY, in Y. sta P8ZP_SCRATCH_W1 sty P8ZP_SCRATCH_W1+1 ldy #0 - lda (P8ZP_SCRATCH_W1),y beq + iny bne - + rts .pend containment_bytearray .proc ; -- check if a value exists in a byte array. ; parameters: P8ZP_SCRATCH_W1: address of the byte array, A = byte to check, Y = length of array (>=1). ; returns boolean 0/1 in A. dey - cmp (P8ZP_SCRATCH_W1),y beq + dey cpy #255 bne - lda #0 rts + lda #1 rts .pend containment_wordarray .proc ; -- check if a value exists in a word array. ; parameters: P8ZP_SCRATCH_W1: value to check, P8ZP_SCRATCH_W2: address of the word array, Y = length of array (>=1). ; returns boolean 0/1 in A. dey tya asl a tay - lda P8ZP_SCRATCH_W1 cmp (P8ZP_SCRATCH_W2),y bne + lda P8ZP_SCRATCH_W1+1 iny cmp (P8ZP_SCRATCH_W2),y beq _found dey + dey dey cpy #254 bne - lda #0 rts _found lda #1 rts .pend