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289037a3dd
HL, instead of being preserved, is set to the character following the last read character.
151 lines
2.8 KiB
NASM
151 lines
2.8 KiB
NASM
; cmd - parse and interpret command
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;
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; *** Consts ***
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; address type
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.equ ABSOLUTE 0
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; handles +, - and ".". For +, easy. For -, addr is negative. For ., it's 0.
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.equ RELATIVE 1
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.equ EOF 2
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; *** Variables ***
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; An address is a one byte type and a two bytes line number (0-indexed)
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.equ CMD_ADDR1 CMD_RAMSTART
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.equ CMD_ADDR2 @+3
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.equ CMD_TYPE @+3
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.equ CMD_RAMEND @+1
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; *** Code ***
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; Parse command line that HL points to and set unit's variables
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; Sets Z on success, unset on error.
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cmdParse:
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ld a, (hl)
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cp 'q'
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jr z, .simpleCmd
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cp 'w'
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jr z, .simpleCmd
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ld ix, CMD_ADDR1
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call .readAddr
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ret nz
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; Before we check for the existence of a second addr, let's set that
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; second addr to the same value as the first. That's going to be its
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; value if we have to ",".
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ld a, (ix)
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ld (CMD_ADDR2), a
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ld a, (ix+1)
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ld (CMD_ADDR2+1), a
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ld a, (ix+2)
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ld (CMD_ADDR2+2), a
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ld a, (hl)
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cp ','
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jr nz, .noaddr2
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inc hl
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ld ix, CMD_ADDR2
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call .readAddr
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ret nz
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.noaddr2:
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; We expect HL (rest of the cmdline) to be a null char or an accepted
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; cmd, otherwise it's garbage
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ld a, (hl)
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or a
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jr z, .nullCmd
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cp 'p'
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jr z, .okCmd
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cp 'd'
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jr z, .okCmd
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cp 'a'
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jr z, .okCmd
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cp 'i'
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jr z, .okCmd
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; unsupported cmd
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ret ; Z unset
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.nullCmd:
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ld a, 'p'
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.okCmd:
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ld (CMD_TYPE), a
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ret ; Z already set
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.simpleCmd:
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; Z already set
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ld (CMD_TYPE), a
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ret
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; Parse the string at (HL) and sets its corresponding address in IX, properly
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; considering implicit values (current address when nothing is specified).
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; advances HL to the char next to the last parsed char.
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; It handles "+" and "-" addresses such as "+3", "-2", "+", "-".
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; Sets Z on success, unset on error. Line out of bounds isn't an error. Only
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; overflows.
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.readAddr:
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ld a, (hl)
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cp '+'
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jr z, .plusOrMinus
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cp '-'
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jr z, .plusOrMinus
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cp '.'
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jr z, .dot
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cp '$'
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jr z, .eof
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; inline parseDecimalDigit
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add a, 0xff-'9'
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sub 0xff-9
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jr c, .notHandled
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; straight number
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ld a, ABSOLUTE
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ld (ix), a
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call parseDecimal
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ret nz
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dec de ; from 1-based to 0-base
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jr .end
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.dot:
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inc hl ; advance cmd cursor
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; the rest is the same as .notHandled
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.notHandled:
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; something else. It's probably our command. Our addr is therefore "."
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ld a, RELATIVE
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ld (ix), a
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xor a ; sets Z
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ld (ix+1), a
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ld (ix+2), a
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ret
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.eof:
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inc hl ; advance cmd cursor
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ld a, EOF
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ld (ix), a
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ret ; Z set during earlier CP
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.plusOrMinus:
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push af ; preserve that + or -
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ld a, RELATIVE
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ld (ix), a
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inc hl ; advance cmd cursor
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ld a, (hl)
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ld de, 1 ; if .pmNoSuffix
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; inline parseDecimalDigit
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add a, 0xff-'9'
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sub 0xff-9
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jr c, .pmNoSuffix
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call parseDecimal ; --> DE
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.pmNoSuffix:
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pop af ; bring back that +/-
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cp '-'
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jr nz, .end
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; we had a "-". Negate DE
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push hl
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ld hl, 0
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sbc hl, de
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ex de, hl
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pop hl
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.end:
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; we still have to save DE in memory
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ld (ix+1), e
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ld (ix+2), d
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cp a ; ensure Z
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ret
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