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-rw-r--r--programs/lexer.s231
-rw-r--r--programs/subasm.s92
-rw-r--r--programs/subeditor.s20
-rw-r--r--programs/utils.s257
4 files changed, 556 insertions, 44 deletions
diff --git a/programs/lexer.s b/programs/lexer.s
new file mode 100644
index 0000000..cd5bb54
--- /dev/null
+++ b/programs/lexer.s
@@ -0,0 +1,231 @@
+; Lexer, and supporting routines for SuBAsm.
+
+; Enums.
+
+; Directives.
+DIR_ORG = 0 ; Origin.
+DIR_BYTE = 1 ; Byte = 8 bits.
+DIR_WORD = 2 ; Word = 16 bits.
+DIR_DWORD = 3 ; Dword = 32 bits.
+DIR_QWORD = 4 ; Qword = 64 bits.
+DIR_INCL = 5 ; Include.
+
+; Tokens.
+TOK_DIR = 0 ; Directive.
+TOK_LOCAL = 1 ; Local syobol.
+TOK_LABEL = 2 ; Label.
+TOK_SYM = 3 ; Symbol.
+TOK_EXPR = 4 ; Expression.
+TOK_CSV = 5 ; Comma separated value.
+TOK_STR = 6 ; String.
+TOK_CHAR = 7 ; Character.
+TOK_IND = 8 ; Indirect addressing.
+TOK_IMM = 9 ; Immediate data.
+TOK_MNE = 10 ; Opcode/Mnemonic.
+TOK_RS = 11 ; Register size prefix.
+TOK_COMM = 12 ; Comment.
+TOK_HEX = 13 ; Hex value.
+TOK_DEC = 14 ; Decimal value.
+TOK_BIN = 15 ; Binary value.
+TOK_INCL = 16 ; Include file.
+
+; Pre-Tokens.
+PTOK_DOT = 0 ; .
+PTOK_AT = 1 ; @
+PTOK_COLON = 2 ; :
+PTOK_EQU = 3 ; =
+PTOK_PLUS = 4 ; +
+PTOK_MINUS = 5 ; -
+PTOK_GT = 6 ; >
+PTOK_LT = 7 ; <
+PTOK_LBRAK = 8 ; (
+PTOK_RBRAK = 9 ; )
+PTOK_COMMA = 10 ; ,
+PTOK_X = 11 ; x
+PTOK_Y = 12 ; y
+PTOK_DQUOT = 13 ; "
+PTOK_SQUOT = 14 ; '
+PTOK_HASH = 15 ; #
+PTOK_SCOLN = 16 ; ;
+PTOK_DOLR = 17 ; $
+PTOK_PRCNT = 18 ; %
+PTOK_NUM = 19 ; 0-9
+PTOK_ALPH = 20 ; a-z A-Z
+PTOK_OTHR = 21 ; Everything else.
+
+; Expressions.
+EXPR_PLUS = 0 ; Plus.
+EXPR_MINUS = 1 ; Minus.
+EXPR_LOW = 2 ; Lower half of address.
+EXPR_HIGH = 3 ; Upper half of address.
+EXPR_NONE = 4 ; No expression.
+
+
+; Data.
+.org lexer_data
+; Jump table for parsing pre-tokens.
+swtab:
+ .word ptok_dot ; PTOK_DOT
+ .word ptok_at ; PTOK_AT
+ .word ptok_col ; PTOK_COLON
+ .word ptok_equ ; PTOK_EQU
+ .word ptok_plus ; PTOK_PLUS
+ .word ptok_min ; PTOK_MINUS
+ .word ptok_gt ; PTOK_GT
+ .word ptok_lt ; PTOK_LT
+ .word ptok_lbrk ; PTOK_LBRAK
+ .word ptok_rbrk ; PTOK_RBRAK
+ .word ptok_com ; PTOK_COMMA
+ .word ptok_xr ; PTOK_X
+ .word ptok_yr ; PTOK_Y
+ .word ptok_dqu ; PTOK_DQUOT
+ .word ptok_squ ; PTOK_SQUOT
+ .word ptok_hash ; PTOK_HASH
+ .word ptok_scol ; PTOK_SCOLN
+ .word ptok_dolr ; PTOK_DOLR
+ .word ptok_prcn ; PTOK_PRCNT
+ .word ptok_num ; PTOK_NUM
+ .word ptok_alph ; PTOK_ALPH
+ .word ptok_othr ; PTOK_OTHR
+
+; Data entry point for utility subroutines.
+util_data:
+
+
+; Program code.
+.org lexer
+lex:
+ ldx #0 ; Reset X.
+ txa ; Reset A.
+ phy #2 ; Preserve the screen buffer index.
+ txy ; Reset Y.
+ sty.q idx0 ; Clear the first index.
+ sty.q idx1 ; Clear the second index.
+ sty.q idx2 ; Clear the third index.
+; lda (ptr), y ; Get a character from the line.
+; pha #1 ; Preserve the character.
+; jsr isdigit ; Is this character a digit?
+; pla #1 ; Get the character back.
+@getline:
+ lda #2 ; Get the third byte, of the line table address.
+ lsl #$10 ; Shift it by 2 bytes.
+ ldb #1 ; Set the second pointer
+ lda.w ltok ; to the last line.
+ jsr set_ptr ;
+ lda.w (ptr2) ; Get the next line.
+ jsr set_ptr ; Set the second pointer to the next line.
+ sta.w ctok ; Make it the current line.
+ and #0 ; Reset A.
+@loop:
+ ldy.w idx0 ; Get the string index.
+ lda (ptr), y ; Get a character from the line.
+ jsr isdelm ; Get the delimiter.
+ cmp #1 ; Are we at the end of the line?
+ beq @end ; Yes, so we're done.
+@spaces:
+ ldy.w idx0 ; Get the string index.
+ inc.w idx0 ; Increment the string index.
+ lda (ptr), y ; Get a character from the line.
+ pha #1 ; Preserve the character.
+ jsr isdelm ; Get the delimiter.
+ and #$10 ; Is this character, a space, or tab?
+ pla #1 ; Get the character back.
+ beq @isstart ; No, so check for the start of the line.
+ cmp #' ' ; Is this character, a space?
+ beq @incs ; Yes, so increment the starting space count.
+ cmp #'\t' ; No, but is it a tab?
+ beq @inct ; Yes, so increment the starting tab count.
+ jmp @spaces ; No, so keep looping.
+@incs:
+ inc idx1 ; Increment the space count.
+ jmp @spaces ; Keep looping.
+@inct:
+ inc idx1+1 ; Increment the tab count.
+ jmp @spaces ; Keep looping.
+@isstart:
+ pha #2 ; Preserve the character.
+ lda.w idx1 ; Was there any whitespace?
+ pla #2 ; Get the character back.
+ beq @switch ; No, so start lexing.
+ cpb #1 ; Yes, and are we at the start of the line?
+ bne @switch ; No, so start lexing.
+@whtspace:
+ ldy #2 ; Yes, so set the line index to the starting whitespace counters.
+ lda.w idx1 ; Get both indecies.
+ sta.w (ptr2), y ; Save them in the line.
+ and #0 ; Reset A.
+ sta.w idx1 ; Reset the second index.
+ deb ; Set the isstart flag to false.
+@switch:
+ jsr get_ptok ; Get the pre-token.
+ jsr parse_ptok ; Parse the pre-token.
+ beq @end ; We got to the end of the string.
+ jmp @loop ; Keep looping.
+@end:
+ ply #2 ; Get the screen buffer index back.
+ rts ; End of lex.
+
+parse_ptok:
+ pha #1 ; Preserve the pre-token.
+ ldb #2 ; Set the third pointer
+ lda.w #swtab ; to the start of the jump table.
+ jsr set_ptr ;
+ and #0 ; Reset A.
+ pla #1 ; Get the pre-token back.
+ phy #2 ; Preserve Y.
+ lsl #1 ; Multiply the pre-token by two, to get the jump index.
+ tay ; Get the index of the jump table.
+ lda.w (ptr3), y ; Get the address to jump to.
+ jsr set_ptr ; Set the third pointer to the case address.
+ and #0 ; Reset A.
+ tab ; Reset B.
+ ply #2 ; Get Y back.
+ jmp (ptr3) ; Jump to the case label.
+ptok_dot:
+ rts ; End of parse_ptok.
+ptok_at:
+ rts ; End of parse_ptok.
+ptok_col:
+ rts ; End of parse_ptok.
+ptok_equ:
+ rts ; End of parse_ptok.
+ptok_plus:
+ rts ; End of parse_ptok.
+ptok_min:
+ rts ; End of parse_ptok.
+ptok_gt:
+ rts ; End of parse_ptok.
+ptok_lt:
+ rts ; End of parse_ptok.
+ptok_lbrk:
+ rts ; End of parse_ptok.
+ptok_rbrk:
+ rts ; End of parse_ptok.
+ptok_com:
+ rts ; End of parse_ptok.
+ptok_xr:
+ rts ; End of parse_ptok.
+ptok_yr:
+ rts ; End of parse_ptok.
+ptok_dqu:
+ rts ; End of parse_ptok.
+ptok_squ:
+ rts ; End of parse_ptok.
+ptok_hash:
+ rts ; End of parse_ptok.
+ptok_scol:
+ rts ; End of parse_ptok.
+ptok_dolr:
+ rts ; End of parse_ptok.
+ptok_prcn:
+ rts ; End of parse_ptok.
+ptok_num:
+ rts ; End of parse_ptok.
+ptok_alph:
+ rts ; End of parse_ptok.
+ptok_othr:
+ rts ; End of parse_ptok.
+
+
+; Entry point for utility subroutines.
+utils:
diff --git a/programs/subasm.s b/programs/subasm.s
index 4cec219..3c8e767 100644
--- a/programs/subasm.s
+++ b/programs/subasm.s
@@ -5,6 +5,7 @@
MAX_SYM = $800 ; Max symbol size.
+.include "lexer.s"
.include "utils.s"
.org incl
@@ -16,7 +17,7 @@ asm_ver:
; Directives.
dir:
- .byte "org",
+ .byte "org"
.byte "byte"
.byte "word"
.byte "dword"
@@ -152,8 +153,8 @@ cmd_srt:
.word run
.word set
-; Data entry point for utility subroutines.
-util_data:
+; Data entry point for the lexer.
+lexer_data:
; Token table.
@@ -185,27 +186,25 @@ idx2:
idx3:
.qword 0
+; Current token line.
+ctok:
+ .word 0
+
+; Last token line.
+ltok:
+ .word 0
+
; Lexeme string.
lexeme:
-; Symbol tables.
+; Symbol table.
.org lexeme+$100
-sym_val:
-.org sym_val+$4000
-sym_id:
-.org sym_id+$1000
-sym_def:
-.org sym_def+$100
-sym_name:
+sym:
; Fixup table.
; Fixups are unresolved symbols.
-.org sym_name+$1000
-fix_sym:
-.org fix_sym+$1000
-fix_ln:
-.org fix_ln+$1000
-fix_val:
+.org sym+$8000
+fix:
; Start of program code.
@@ -217,16 +216,12 @@ subasm:
tba ; Reset A.
tax ; Reset X.
jsr chk_shcmd ; Did we get a shortend command?
- bne parse_cmd ; Yes, so skip everything else.
- jmp @end ;
+ bne @cmd ; Yes, so skip everything else.
jsr chk_cmd ; No, but did we get a full command?
- bne parse_cmd ; Yes, so skip everything else.
- jsr lexer ; No, so start lexing this line.
-@end:
-subasm_end:
- rts ; End of subasm.
-
-parse_cmd:
+ bne @cmd ; Yes, so skip everything else.
+ jsr lex ; No, so start lexing this line.
+ jmp @end ; We are done.
+@cmd:
ldb #1 ; Set the second pointer
lda.d #cmd_srt ; to the command subroutine table.
jsr set_ptr ;
@@ -234,7 +229,7 @@ parse_cmd:
tba ; Reset A.
lda f ; Get the command ID.
cmp #8 ; Is the command ID greater than the command count?
- bcs subasm_end ; Yes, so we're done.
+ bcs @end ; Yes, so we're done.
lsl #1 ; No, so multiply the command ID by two.
phy #2 ; Preserve the screen buffer position.
tay ; Set the index to the offset that we just calculated.
@@ -244,7 +239,8 @@ parse_cmd:
jsr set_ptr ;
ldb #0 ; Reset B.
jsr (ptr3) ; Run the command's subroutine.
- jmp subasm_end ; We are done.
+@end:
+ rts ; End of subasm.
chk_shcmd:
tba ; Reset A.
@@ -259,6 +255,7 @@ chk_shcmd:
beq @false ; Yes, so return that we failed.
cmp #' ' ; No, but is this character, a space?
beq @false ; Yes, so return that we failed.
+ jsr tolower ; No, so convert it to lowercase.
@loop:
ldb (ptr2), y ; Are we at the end of the table?
beq @false ; Yes, so return that we failed.
@@ -286,6 +283,41 @@ chk_shcmd:
rts ; End of chk_shcmd.
+chk_cmd:
+ tba ; Reset A.
+ tax ; Reset X.
+ sta.q idx0 ; Reset the first index.
+ sta.q idx1 ; Reset the second index.
+@loop:
+ lda.w #cmds ; Get pointer to the start of the command table.
+ clc ; Prepare for a non carrying add.
+ adc.w idx0 ; Offset the pointer, by the length of the previous string.
+ pha #8 ; Preserve the command string pointer.
+ jsr strcasecmp ; Is the command buffer, the same as the command string?
+ pla #8 ; Get the command string pointer back.
+ beq @true ; Yes, so return true.
+ ldb idx1 ; No, so Get the command ID.
+ cpb #7 ; Have we reached the end of the command table?
+ beq @false ; Yes, so return false.
+ inc idx1 ; No, so increment the command ID.
+@getlen:
+ jsr strlen ; Get the string's length.
+ inx ; Add one to the length.
+ txa ; Place it in the accumulator.
+ clc ; Prepare for a non carrying add.
+ adc.w idx0 ; Add the string offset to the current length
+ sta.w idx0 ; Save the offset in the first index.
+ jmp @loop ; Keep looping.
+@true:
+ ldb idx1 ; Get the command ID.
+ stb f ; Return the command ID.
+ ldb #1 ; Return true.
+ jmp @end ; We are done.
+@false:
+ ldb #0 ; Return false.
+@end:
+ rts ; End of chk_cmd.
+
viewmem:
lda.q prg_cnt ; Get the program counter.
sta.q idx0 ; Save the address in the first index.
@@ -347,7 +379,5 @@ set:
@end:
rts ; End of set.
-
; Entry point for utility subroutines.
-utils:
-
+lexer:
diff --git a/programs/subeditor.s b/programs/subeditor.s
index 26c6f7d..1768d62 100644
--- a/programs/subeditor.s
+++ b/programs/subeditor.s
@@ -1058,8 +1058,10 @@ update_pos:
adc scr_str ; with the starting line number to get the absolute line number.
tay ; Place it in the Y regster for now.
mul #maxcol+1 ; Multiply the line number by the screen's max column count, plus 1.
+ clc ; Clear the carry flag.
adc scr_col ; Add the cursor's column number to get the screen index.
tay ; Place the index into the Y register.
+ tba ; Reset A.
lda #$1B ; Print an escape character
sta scr ; to the screen.
lda #'[' ; Print '['
@@ -1072,27 +1074,19 @@ update_pos:
getrow:
lda scr_row ; Get the cursor's y coordinate.
- div #10 ; Divide A by 10.
- adc #'0' ; Convert it to ascii, and
- sta scr ; print to the screen.
- tba ; Get the remainder.
- adc #'0' ; Convert it to ascii, and
- sta scr ; print to the screen.
- rts ; End of getrow.
-
+ jmp bcd ; Convert it to BCD.
getcol:
lda #';' ; Print ';'
sta scr ; to the screen.
lda scr_col ; Get the cursor's x coordinate.
+bcd:
div #10 ; Divide A by 10.
- clc ;
- adc #'0' ; Convert it to ascii, and
+ ora #'0' ; Convert it to ascii, and
sta scr ; print to the screen.
tba ; Get the remainder.
- clc
- adc #'0' ; Convert it to ascii, and
+ ora #'0' ; Convert it to ascii, and
sta scr ; print to the screen.
- rts ; End of getrow.
+ rts ; End of bcd.
scrl_down:
inc scr_str ; Increment the starting line of the screen.
diff --git a/programs/utils.s b/programs/utils.s
index 6032a47..d8d4aa2 100644
--- a/programs/utils.s
+++ b/programs/utils.s
@@ -5,6 +5,16 @@
hex_char:
.byte "0123456789ABCDEF"
+; Compare, and return table for pre-tokens.
+ptok_tab:
+ .byte ".@:=+-><(),xy\"\'#;$%"
+; Compare, and return table for isdelm.
+dtab:
+ .byte "\n,\"\' "
+; Compare, and return table for isdelm2.
+dtab2:
+ .byte "),.+<>-=;\n"
+
.org utils
print_hi:
@@ -134,3 +144,250 @@ charcpy:
sta strbuf, x ; Save it in the string buffer.
inc idx3 ; Increment the string index.
rts ; End of charcpy.
+
+
+strlen:
+ ldb #1 ; Set the second pointer
+ jsr set_ptr ; to the passed pointer.
+ deb ; Reset B.
+ tba ; Reset A.
+ tax ; Reset X.
+ phy #2 ; Preserve Y.
+ txy ; Reset Y.
+@loop:
+ lda (ptr2), y ; Are we at the end of the string?
+ beq @end ; Yes, so we're done.
+ iny ; No, so increment the index.
+ jmp @loop ; Keep looping.
+@end:
+ tyx ; Return the length in X.
+ ply #2 ; Get the preserved value back.
+ rts ; End of strlen.
+
+
+strcmp:
+ ldb #1 ; Set the second pointer
+ jsr set_ptr ; to the passed pointer.
+ deb ; Reset B.
+ tba ; Reset A.
+ phy #2 ; Preserve Y.
+ tay ; Reset Y.
+@loop:
+ ldb #0 ; Set the islong flag to false.
+ lda (ptr), y ; Are we at the end of the first string?
+ beq cmpr ; Yes, so check if we're too short, or too long.
+ ldb #1 ; No, so set the islong flag to true.
+ cmp (ptr2), y ; Is the character of both strings, the same?
+ bne cmpr ; No, so check if we're too short, or too long.
+ iny ; Yes, so increment the index.
+ jmp @loop ; Keep looping.
+
+strcasecmp:
+ ldb #1 ; Set the second pointer
+ jsr set_ptr ; to the passed pointer.
+ deb ; Reset B.
+ tba ; Reset A.
+ phy #2 ; Preserve Y.
+ tay ; Reset Y.
+@loop:
+ ldb #0 ; Set the islong flag to false.
+ lda (ptr), y ; Are we at the end of the first string?
+ beq cmpr ; Yes, so check if we're too short, or too long.
+ ldb #1 ; No, so set the islong flag to true.
+ jsr tolower ; Convert the character of string 1 to lowercase.
+ phb #1 ; Preserve the islong flag.
+ pha #1 ; Preserve the converted character.
+ lda (ptr2), y ; Get the character of the second string.
+ jsr tolower ; Convert the character of string 2 to lowercase.
+ tab ; Place it in B.
+ pla #1 ; Get the character of string 1 back.
+ cab ; Is the character of both strings, the same?
+ plb #1 ; Get the islong flag back.
+ bne cmpr ; No, so check if we're too short, or too long.
+ iny ; Yes, so increment the index.
+ jmp @loop ; Keep looping.
+
+cmpr:
+ lda (ptr2), y ; Are we at the end of the second string?
+ beq @islong ; Yes, so check the islong flag.
+@isshort:
+ lda (ptr), y ; No, but are we at the end of the first string?
+ beq @short ; Yes, so return -1.
+@islong:
+ cpb #1 ; Is the islong flag true?
+ bne @equ ; No, so return 0.
+@long:
+ lda #1 ; Yes, so return 1.
+ jmp @end ; We are done.
+@equ:
+ lda #0 ; Return 0.
+ jmp @end ; We are done.
+@short:
+ lda #$FF ; Return -1.
+@end:
+ ply #2 ; Get the preserved value back.
+ rts ; End of strcmp.
+
+
+isdigit:
+ sec ; Prepare for a non carrying subtraction.
+ sbc #'0' ; Subtract $30 from the passed character.
+ and #$FF ; Make sure that we have only one byte.
+ cmp #10 ; Is the subtracted value, less than 10?
+ bcs @false ; No, so return false.
+@true:
+ lda #1 ; Yes, so return true.
+ jmp @end ; We are done.
+@false:
+ lda #0 ; Return false.
+@end:
+ rts ; End of isdigit.
+
+isxdigit:
+ pha #1 ; Preserve the character.
+ jsr isdigit ; Is this character, a decimal digit?
+ pla #1 ; Get the character back.
+ bne @true ; Yes, so return true.
+@alpha:
+ sec ; No, so prepare for a non carrying subtract.
+ ora #$20 ; Convert it to lowercase.
+ sbc #'a' ; Subtract $61 from the character.
+ and #$FF ; Make sure that we have only one byte.
+ cmp #6 ; Is the subtracted value, less than 6?
+ bcs @false ; No, so return false.
+@true:
+ lda #1 ; Yes, so return true.
+ jmp @end ; We are done.
+@false:
+ lda #0 ; Return false.
+@end:
+ rts ; End of isxdigit.
+
+
+isupper:
+ sec ; Prepare for a non carrying subtraction.
+ sbc #'A' ; Subtract $41 from the passed character.
+ jmp isletter ; Check if it's less than 26.
+islower:
+ sec ; Prepare for a non carrying subtraction.
+ sbc #'a' ; Subtract $61 from the passed character.
+isletter:
+ and #$FF ; Make sure that we have only one byte.
+ cmp #26 ; Is the subtracted value, less than 26?
+ bcs @false ; No, so return false.
+@true:
+ lda #1 ; Yes, so return true.
+ jmp @end ; We are done.
+@false:
+ lda #0 ; Return false.
+@end:
+ rts ; End of isletter.
+
+
+tolower:
+ pha #1 ; Preserve the character.
+ jsr isupper ; Is this character, an uppercase character?
+ pla #1 ; Get the character back.
+ beq @end ; No, so we're done.
+@lower:
+ ora #$20 ; Yes, so convert it to lowercase.
+@end:
+ rts ; End of tolower.
+
+
+toupper:
+ pha #1 ; Preserve the character.
+ jsr islower ; Is this character, a lowercase character?
+ pla #1 ; Get the character back.
+ beq @end ; No, so we're done.
+@upper:
+ and #$5F ; Yes, so convert it to uppercase.
+@end:
+ rts ; End of toupper.
+
+
+isdelm2:
+ ldx #0 ; Reset X.
+@loop:
+ ldb dtab2, x ; Get the compare value.
+ beq @other ; We hit the end of the table, so check for the others.
+ cab ; Are they the same?
+ beq @r1 ; Yes, so return 1.
+ inx ; No, so increment the table index.
+ jmp @loop ; Keep looping.
+@other:
+ ldx #0 ; Reset X.
+ cmp #0 ; Is this a null terminator?
+ beq @r1 ; Yes, so return 1.
+ cmp #'\t' ; No, but is it a tab?
+ beq @r2 ; Yes, so return 2.
+ cmp #' ' ; No, but is it a space?
+ beq @r2 ; Yes, so also return 2.
+@r0:
+ lda #0 ; Return 0.
+ rts ; End of isdelm2.
+@r1:
+ ldx #0 ; Reset X.
+ lda #1 ; Return 1.
+ rts ; End of isdelm2.
+@r2:
+ lda #2 ; Return 2.
+ rts ; End of isdelm2.
+
+
+isdelm:
+ ldx #0 ; Reset X.
+@loop:
+ ldb dtab, x ; Get the compare value.
+ beq @other ; We hit the end of the table, so check for the others.
+ cab ; Are they the same?
+ beq @rshft ; Yes, so return 1 << index.
+ inx ; No, so increment the table index.
+ jmp @loop ; Keep looping.
+@other:
+ ldx #0 ; Reset X.
+ cmp #0 ; Is this a null terminator?
+ beq @rshft ; Yes, so return 1.
+ ldx #4 ; No, so set the shift amount to 4.
+ cmp #'\t' ; Is this a tab?
+ beq @rshft ; Yes, so return 16.
+ ldx #0 ; No, so reset X.
+@r0:
+ lda #0 ; Return 0.
+ rts ; End of isdelm.
+@rshft:
+ stx a ; Save the shift value.
+ ldx #0 ; Reset X.
+ lda #1 ; Set up the bitshift.
+ lsl a ; Return 1 << X.
+ rts ; End of isdelm.
+
+
+get_ptok:
+ ldx #0 ; Reset X.
+ jsr tolower ; Conver the character to lowercase.
+@loop:
+ ldb ptok_tab, x ; Get the compare value.
+ beq @other ; We hit the end of the table, so check for the others.
+ cab ; Are they the same?
+ beq @rtab ; Yes, so return X.
+ inx ; No, so increment the table index.
+ jmp @loop ; Keep looping.
+@rtab:
+ txa ; Return X.
+ rts ; End of get_ptok.
+@other:
+ tab ; Preserve the character.
+ jsr isdigit ; Is this character a digit?
+ bne @rnum ; Yes, so return PTOK_NUM.
+ tba ; No, so get the character back.
+ jsr islower ; Is it an alphabetical character?
+ bne @ralph ; Yes, so return PTOK_ALPH.
+ lda #PTOK_OTHR ; No, so return PTOK_OTHR.
+ rts ; End of get_ptok.
+@rnum:
+ lda #PTOK_NUM ; Return PTOK_NUM.
+ rts ; End of get_ptok.
+@ralph:
+ lda #PTOK_ALPH ; Return PTOK_ALPH.
+ rts ; End of get_ptok.