Label Replacer

The label replacer for the Nibble Knowledge CPU

LR4

LR4 is the label replacer written in C99 for the Nibble Knowledge CPU. It is under 500 lines of executable code, and simply replaces labels in an AS4 assembly file based on a simple definition file.

LR4 also strips comments and whitespace to ease the job of AS4.

Useage

There is only one invocation of lr4:

• ./lr4 DEFINITION_FILE INPUT_ASSEMBLY OUTPUT_ASSEMBLY

Where DEFINITION_FILE is the label replacement definition file, INPUT_ASSEMBLY is the AS4 assembly file that requires replacement, and OUTPUT_ASSEMBLY is the output assembly file.

Definition Files

Definition files have a very simple format. There are only 2 allowed constructs:

• Comments: prefixed with either ";" or "#" as in AS4.
• Replacements: these are in the form LABEL_NAME: ADDRESS. Every instance of LABEL_NAME in the input assembly file will be replaced with ADDRESS, optionally with an additional offset if LABEL_NAME is used in the form LABEL_NAME[OFFSET] in the input assembly file.
• ADDRESS and OFFSET may be in hexadecimal, decimal, octal or binary. However, the rules slightly differ for each case.
  • In the case of ADDRESS: hexadecimal must be prefixed with "0x", and decimal is either without prefix or with "0d".
  • In the case of OFFSET: hexadecimal may be without prefix or with "0x", but decimal requires a "0d" prefix. This is to accomodate the macro assembler.
  • Octal always requires a prefix, either "0" or "0o"; and binary always requires the prefix "0b".

INF header

LR4 also generates INF headers for AS4 if prompted, either by using the syntax "INF BASE_ADDRESS" or by utilising the same syntax as required in AS4 but excluding any data section information (as LR4 generates this). Examples are below:

• INF BASE_ADDRESS:

INF 0x16
LOD data
HLT
data: .data 1 0x0

• Detailed INF:

INF
PINF
BADR 0x16
EPINF
EINF
LOD data
HLT
data: .data 1 0x0

• Both will become:

INF
PINF
BADR 0x0016
EPINF
DSEC D_SEC
DNUM 0x1
DSIZE 0x1
EINF
LOD data
HLT
D_SEC: data: .data 1 0x0

Custom pseudo instructions will be passed through untouched in the PINF...EPINF section. BADR must precede all pseudo instructions.

The metadata pseudoinstruction "N_START LABEL" will be added to output if an address of operation is performed. It will be placed just before EINF. It is not included in output, it merely informs AS4 of the location of the start of the static number 0-15 in memory.

Example definition file

what: 0xF3
huh: 0b10110
lol: 0453
# commentos
; plenty of them

Example input assembly file

		hey: LOD huh
LOD     lol
    LOD what
LOD huh[0b0011] ;hey
LOD lol[E] #comments
LOD what[0xD]
LOD what[011]
LOD lol[0o11]
LOD huh[0d14]
LOD who
LOD how
#they are useful
LOD no
LOD derp
LOD dope
no: .data 1 0b1010
how: .data 1 010
how2: .data 1 0o10
who: .data 1 0xF
derp: .data 1 12
derp .data 1 0d12
dope: .data 4 no
zurp: .data 4 huh

Example output assembly file

hey: LOD 0x16
LOD 0x12B
LOD 0xF3
LOD 0x19
LOD 0x139
LOD 0x100
LOD 0xFC
LOD 0x134
LOD 0x24
LOD who
LOD how
LOD no
LOD derp
LOD dope
no: .data 1 0b1010
how: .data 1 010
how2: .data 1 0o10
who: .data 1 0xF
derp: .data 1 12
derp .data 1 0d12
dope: .data 4 no
zurp: .data 4 0x16