## Copyright (C) 2016 Jeremiah Orians
## This file is part of stage0.
##
## stage0 is free software: you can redistribute it and/or modify
## it under the terms of the GNU General Public License as published by
## the Free Software Foundation, either version 3 of the License, or
## (at your option) any later version.
##
## stage0 is distributed in the hope that it will be useful,
## but WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
## GNU General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with stage0.  If not, see <http://www.gnu.org/licenses/>.

# ;; R14 will be storing our condition
# ;;
# ;; R13 will be a stack pointer. It will be zero
# ;; on the start, and the stack grows up.
# ;; This means that when stack is used, the
# ;; first instructions of this program will be
# ;; overwritten. But because this is initialization
# ;; code, it is already not used at the time.
# ;; And the stack usage is fixed - there is only one CALL
# ;; instruction in this file
# ;;
# ;; R2 Is our holder.
# ;; It holds the first nybble of the byte till the second iteration
# ;;
# ;; R12 Is our toggle. It is initialized to zero on start.
# ;; When non-zero, it means that we are processing the second nybble
# ;;
# ;; R8 will hold zero. It is initialized to zero on start.

# :start ; offset = 0

# ;; Prepare often-used values that will be held in registers
E0002D2F000f # LOADUI R15 0xF ; Set R15 to 0xF
E0002D2B1101 # LOADUI R11 0x1101 ; R11 will hold 0x1101

# ;; Prep TAPE_01
01100FB8     # MUX R0 R15 R11 R8 ; 0x1100 = ((0x1101 & ~0xF) | (0 | 0xF))
42100001     # FOPEN_WRITE

# ;; Prep TAPE_02
0900040B     # COPY R0 R11 ; 0x1101
42100001     # FOPEN_WRITE

# :loop ; offset = 1c
0D000021     # FALSE R1 ; Read from tty
42100100     # FGETC ; Read a Char
E000A030000d # CMPSKIPI.NE R0 13 ; Replace all CR
E0002D20000a # LOADUI R0 10 ; WIth LF
42100200     # FPUTC

# ; Display the Char to User

# ;; Check for Ctrl-D
E000A0300004 # CMPSKIPI.NE R0 4
3C000104     # JUMP @finish

# ;; Check for EOF
E0002CC000fe # JUMP.NP R0 @finish

# ;; Write out unprocessed byte
0900041B     # COPY R1 R11 ; Write to TAPE_02
42100200     # FPUTC ; Print the Char

# ;; Convert byte to nybble
E0002D0D0036 # CALLI R13 @hex ; Convert it

# ;; Get another byte if nonhex
E0002CC0ffc4 # JUMP.NP R0 @loop ; Don't use nonhex chars

# ;; Deal with the case of second nybble
E0002CAC000c # JUMP.NZ R12 @second_nybble ; Jump if toggled

# ;; Process first byte of pair
0502020F     # AND R2 R0 R15 ; Store First nibble
0D00003C     # TRUE R12 ; Flip the toggle
3C00ffb2     # JUMP @loop

# ;; Combined second nybble in pair with first

# :second_nybble ; offset = 6a
E0002D520004 # SL0I R2 4 ; Shift our first nibble
0502000F     # AND R0 R0 R15 ; Mask out top
05000002     # ADD R0 R0 R2 ; Combine nibbles

# ;; Writeout and prepare for next cycle
0D00002C     # FALSE R12 ; Flip the toggle

# ; Write the combined byte
01101FB8     # MUX R1 R15 R11 R8 ; To TAPE_01 
42100200     # FPUTC
3C00ff94     # JUMP @loop ; Try to get more bytes

# :hex ; offset = 88

# ;; Deal with line comments starting with #
E1001FE00023 # CMPUI R14 R0 35
E0002C5E007e # JUMP.E R14 @ascii_comment

# ;; Deal with line comments starting with ;
E1001FE0003b # CMPUI R14 R0 59
E0002C5E0072 # JUMP.E R14 @ascii_comment

# ;; Deal with all ascii less than '0'
E1001FE00030 # CMPUI R14 R0 48
E0002C8E005e # JUMP.L R14 @ascii_other

# ;; Deal with '0'-'9'
E1001FE00039 # CMPUI R14 R0 57
E0002C7E0034 # JUMP.LE R14 @ascii_num

# ;; Deal with all ascii less than 'A'
E1001FE00041 # CMPUI R14 R0 65
E0002C8E0046 # JUMP.L R14 @ascii_other

# ;; Deal with 'A'-'F'
E1001FE00046 # CMPUI R14 R0 70
E0002C7E0030 # JUMP.LE R14 @ascii_high

# ;; Deal with all ascii less than 'a'
E1001FE00061 # CMPUI R14 R0 97
E0002C8E002e # JUMP.L R14 @ascii_other

# ;;  Deal with 'a'-'f'
E1001FE00066 # CMPUI R14 R0 102
E0002C7E000e # JUMP.LE R14 @ascii_low

# ;; Ignore the rest
3C00001e     # JUMP @ascii_other

# :ascii_num ; offset = ec
E10011000030 # SUBUI R0 R0 48
0D01001D     # RET R13

# :ascii_low ; offset = f6
E10011000057 # SUBUI R0 R0 87
0D01001D     # RET R13

# :ascii_high ; offset = 100
E10011000037 # SUBUI R0 R0 55
0D01001D     # RET R13

# :ascii_other ; offset = 10a
0D000030     # TRUE R0
0D01001D     # RET R13

# :ascii_comment ; offset = 112
0D000021     # FALSE R1 ; Read from tty
42100100     # FGETC ; Read another char
E000A030000d # CMPSKIPI.NE R0 13 ; Replace all CR
E0002D20000a # LOADUI R0 10 ; WIth LF
42100200     # FPUTC ; Let the user see it
E1001FE0000a # CMPUI R14 R0 10 ; Stop at the end of line
0900041B     # COPY R1 R11 ; Write to TAPE_02
42100200     # FPUTC ; The char we just read
E0002C6Effd4 # JUMP.NE R14 @ascii_comment ; Otherwise keep looping
3C00ffc8     # JUMP @ascii_other

# :finish ; offset = 142
01100FB8     # MUX R0 R15 R11 R8 ; Close TAPE_01 
42100002     # FCLOSE
0900040B     # COPY R0 R11 ; Close TAPE_02
42100002     # FCLOSE
FFFFFFFF     # HALT