Look Up a Bounded Byte Dictionary on Amiga | Pattern Library

An item code, tile identifier or command token often needs a small associated value.

Amiga shows the working diagnostic row 07 01 01 14 03 0A 14 14. — A completed native caller displays 07 01 01 14 03 0A 14 14. The public field order below identifies these bytes; the capture is a state diagnostic, not a recording of a finished game.

Use it in a project

Search COUNT 0–8 key/value pairs stored in K0..K7 and Q0..Q7 respectively. Return the first matching VALUE and FOUND=1; a miss returns zero with FOUND=0. COUNT>8 returns VALID=0. Preserve the dictionary and key. Duplicate keys deliberately use the earliest pair.

Include component.inc once (MOS callers include the shared 6502 implementation through it). Reserve the public fields in this exact order: VALUE, FOUND, VALID, KEY, COUNT, K0, K1, K2, K3, K4, K5, K6, K7, Q0, Q1, Q2, Q3, Q4, Q5, Q6, Q7. They occupy 21 contiguous bytes. Also reserve the private workspace: T0, T1 (2 bytes). Array names in the explanation refer to the numbered consecutive bindings, such as C0, C1 and so on.

Call dictionary_lookup_init once at the intended reset boundary. It clears inputs as well as outputs and workspace. Set your starting state and configuration afterwards, then call dictionary_lookup_step whenever the described event occurs. The helper reads no device, waits for no frame and installs no interrupt handler.

Ownership	Fields
Retain between calls	COUNT and key/value arrays
Supply before service	KEY
Read after service	VALUE, FOUND and VALID

Scan the active prefix and stop at the first equal key. FOUND carries presence separately from VALUE, allowing zero to be valid data.

Reusable initialisation and service

component.inc

; SPDX-License-Identifier: MIT
; Look Up a Bounded Byte Dictionary. See README.md for the byte interface and ownership.
; init clears the public fields and private workspace; set inputs afterwards.
dictionary_lookup_init:
    move.b #0,d0
    move.b d0,VALUE
    move.b d0,FOUND
    move.b d0,VALID
    move.b d0,KEY
    move.b d0,COUNT
    move.b d0,K0
    move.b d0,K1
    move.b d0,K2
    move.b d0,K3
    move.b d0,K4
    move.b d0,K5
    move.b d0,K6
    move.b d0,K7
    move.b d0,Q0
    move.b d0,Q1
    move.b d0,Q2
    move.b d0,Q3
    move.b d0,Q4
    move.b d0,Q5
    move.b d0,Q6
    move.b d0,Q7
    move.b d0,T0
    move.b d0,T1
    rts
dictionary_lookup_step:
; VALUE = 0
    move.b #0,d0
    move.b d0,VALUE
; FOUND = 0
    move.b #0,d0
    move.b d0,FOUND
; VALID = 0
    move.b #0,d0
    move.b d0,VALID
; if COUNT > 8:
    move.b COUNT,d0
    cmp.b #8,d0
    bhi dictionary_lookup_L1
    jmp dictionary_lookup_L2
dictionary_lookup_L1:
; return
    rts
    jmp dictionary_lookup_L3
dictionary_lookup_L2:
dictionary_lookup_L3:
; VALID = 1
    move.b #1,d0
    move.b d0,VALID
; T0 = 0
    move.b #0,d0
    move.b d0,T0
; while T0 < COUNT:
dictionary_lookup_L4:
    move.b T0,d0
    move.b COUNT,d1
    cmp.b d1,d0
    bcs dictionary_lookup_L5
    jmp dictionary_lookup_L6
dictionary_lookup_L5:
; T1 = K[T0]
    moveq #0,d1
    move.b T0,d1
    lea K0,a0
    move.b 0(a0,d1.w),d0
    move.b d0,T1
; if KEY == T1:
    move.b KEY,d0
    move.b T1,d1
    cmp.b d1,d0
    beq dictionary_lookup_L7
    jmp dictionary_lookup_L8
dictionary_lookup_L7:
; T1 = Q[T0]
    moveq #0,d1
    move.b T0,d1
    lea Q0,a0
    move.b 0(a0,d1.w),d0
    move.b d0,T1
; VALUE = T1
    move.b T1,d0
    move.b d0,VALUE
; FOUND = 1
    move.b #1,d0
    move.b d0,FOUND
; return
    rts
    jmp dictionary_lookup_L9
dictionary_lookup_L8:
dictionary_lookup_L9:
; T0 = T0 + 1
    move.b T0,d0
    add.b #1,d0
    move.b d0,T0
    jmp dictionary_lookup_L4
dictionary_lookup_L6:
    rts
component_end:

Machine contract

D0–D3/A0–A1/CCR may change; D4–D7/A2–A6 are preserved. A direct BSR/JSR needs four return-address stack bytes. The helper makes no nested calls and adds no other stack use. Its named scratch is private workspace, not a pointer, a ROM variable or shared zero-page space that the game may borrow concurrently. The samples use fixed symbol bindings. Scope or rename every label and binding, including the component_end measurement marker, and allocate a separate block for each independent instance. Different helpers can also use common field names, so combining them needs separate namespaces or explicitly renamed bindings. Give each block one mutation owner.

The A500 OCS diagnostic cold-boots an OFS disk, owns the Copper and bitplane and disables interrupt/DMA sources. The helper does not take over hardware or allocate Chip RAM.

Adapt the caller

demo.asm supplies the bindings and include order. exercise.inc first runs table cases, then a separate client retaining state between calls. A game can call the public step entry directly and remove the diagnostic packet and display. Do not copy the diagnostic’s hardware takeover into an existing game loop.

Build with make ASM198X=/path/to/asm198x and BUILD198X=/path/to/build198x. The Makefile produces normal, custom, deliberately wrong and repaired programs. Tools must already be installed; the sample downloads nothing.

Bindings and include order

demo.asm

    section code,code_c
CUSTOM = 0
BROKEN = 0
COYOTE_STEPS = 4
BUFFER_STEPS = 4
TEXT_CAP = 8
PROPERTY_COUNT = 16
STREAM_BYTES = 13
CRC_POLY = 7
    include "caller.inc"
    include "exercise.inc"
component_start:
    include "component.inc"
    even
    include "data.inc"
    include "cases.inc"
    even
    include "display.inc"
    include "../../framework/turn-deadline/font.inc"
code_end:
STATE:
VALUE: dc.b 0
FOUND: dc.b 0
VALID: dc.b 0
KEY: dc.b 0
COUNT: dc.b 0
K0: dc.b 0
K1: dc.b 0
K2: dc.b 0
K3: dc.b 0
K4: dc.b 0
K5: dc.b 0
K6: dc.b 0
K7: dc.b 0
Q0: dc.b 0
Q1: dc.b 0
Q2: dc.b 0
Q3: dc.b 0
Q4: dc.b 0
Q5: dc.b 0
Q6: dc.b 0
Q7: dc.b 0
T0: dc.b 0
T1: dc.b 0
    even
ready: dc.w 0
preview: dcb.b 8,0
OUTPUT: dcb.b 1300,0
    even
signature: dc.b "198XTOOLKIT0000",0
    even
copperlist:
    dc.w $08e,$2c81,$090,$2cc1,$092,$0038,$094,$00d0
    dc.w $100,$1200,$102,0,$104,0,$108,0,$10a,0
    dc.w $180,$012,$182,$fff
copbpl:
    dc.w $0e0,0,$0e2,0
    dc.w $ffff,$fffe
plane: dcb.b 10240,0

A client retaining state between calls

exercise.inc, excerpt

preview_rules:
    ifne CUSTOM
; COUNT = 1
    move.b #1,d0
    move.b d0,COUNT
; K0 = 255
    move.b #255,d0
    move.b d0,K0
; Q0 = 0
    move.b #0,d0
    move.b d0,Q0
; KEY = 255
    move.b #255,d0
    move.b d0,KEY
    ifne BROKEN
; KEY = 0
    move.b #0,d0
    move.b d0,KEY
    endif
    bsr checked_step
    bsr emit_state
    rts
    else
; COUNT = 3
    move.b #3,d0
    move.b d0,COUNT
; K0 = 10
    move.b #10,d0
    move.b d0,K0
; K1 = 20
    move.b #20,d0
    move.b d0,K1
; K2 = 20
    move.b #20,d0
    move.b d0,K2
; Q0 = 4
    move.b #4,d0
    move.b d0,Q0
; Q1 = 7
    move.b #7,d0
    move.b d0,Q1
; Q2 = 9
    move.b #9,d0
    move.b d0,Q2
; KEY = 20
    move.b #20,d0
    move.b d0,KEY
    ifne BROKEN
; KEY = 0
    move.b #0,d0
    move.b d0,KEY
    endif
    bsr checked_step
    bsr emit_state
    endif
    rts

Customise it

Look up key 255 whose stored value is zero. The maintained custom caller changes its inputs or client sequence rather than hiding a different implementation behind the same label. Compare every state of the two clients, not only their final display.

Custom client selection

custom.asm

    section code,code_c
CUSTOM = 1
BROKEN = 0
COYOTE_STEPS = 2
BUFFER_STEPS = 2
TEXT_CAP = 4
PROPERTY_COUNT = 16
STREAM_BYTES = 13
CRC_POLY = 49
    include "caller.inc"
    include "exercise.inc"
component_start:
    include "component.inc"
    even
    include "data.inc"
    include "cases.inc"
    even
    include "display.inc"
    include "../../framework/turn-deadline/font.inc"
code_end:
STATE:
VALUE: dc.b 0
FOUND: dc.b 0
VALID: dc.b 0
KEY: dc.b 0
COUNT: dc.b 0
K0: dc.b 0
K1: dc.b 0
K2: dc.b 0
K3: dc.b 0
K4: dc.b 0
K5: dc.b 0
K6: dc.b 0
K7: dc.b 0
Q0: dc.b 0
Q1: dc.b 0
Q2: dc.b 0
Q3: dc.b 0
Q4: dc.b 0
Q5: dc.b 0
Q6: dc.b 0
Q7: dc.b 0
T0: dc.b 0
T1: dc.b 0
    even
ready: dc.w 0
preview: dcb.b 8,0
OUTPUT: dcb.b 1300,0
    even
signature: dc.b "198XTOOLKIT0000",0
    even
copperlist:
    dc.w $08e,$2c81,$090,$2cc1,$092,$0038,$094,$00d0
    dc.w $100,$1200,$102,0,$104,0,$108,0,$10a,0
    dc.w $180,$012,$182,$fff
copbpl:
    dc.w $0e0,0,$0e2,0
    dc.w $ffff,$fffe
plane: dcb.b 10240,0

The custom diagnostic row is 00 01 01 FF 01 FF 00 00. The full client trace in the source explains how it gets there.

Mistake and repair

The wrong caller clears the lookup key. It can turn a valid item into a miss or accidentally resolve key zero. Preserve KEY and distinguish FOUND=0 from a stored zero value.

The BROKEN branch lives in the sequential client, not the reusable helper. wrong.asm selects it; repaired.asm restores the normal call sequence. The repaired executable matches the normal program (for Spectrum, compare loaded CODE rather than the tape filename).

Select the deliberately wrong client

wrong.asm

    section code,code_c
CUSTOM = 0
BROKEN = 1
COYOTE_STEPS = 4
BUFFER_STEPS = 4
TEXT_CAP = 8
PROPERTY_COUNT = 16
STREAM_BYTES = 13
CRC_POLY = 7
    include "caller.inc"
    include "exercise.inc"
component_start:
    include "component.inc"
    even
    include "data.inc"
    include "cases.inc"
    even
    include "display.inc"
    include "../../framework/turn-deadline/font.inc"
code_end:
STATE:
VALUE: dc.b 0
FOUND: dc.b 0
VALID: dc.b 0
KEY: dc.b 0
COUNT: dc.b 0
K0: dc.b 0
K1: dc.b 0
K2: dc.b 0
K3: dc.b 0
K4: dc.b 0
K5: dc.b 0
K6: dc.b 0
K7: dc.b 0
Q0: dc.b 0
Q1: dc.b 0
Q2: dc.b 0
Q3: dc.b 0
Q4: dc.b 0
Q5: dc.b 0
Q6: dc.b 0
Q7: dc.b 0
T0: dc.b 0
T1: dc.b 0
    even
ready: dc.w 0
preview: dcb.b 8,0
OUTPUT: dcb.b 1300,0
    even
signature: dc.b "198XTOOLKIT0000",0
    even
copperlist:
    dc.w $08e,$2c81,$090,$2cc1,$092,$0038,$094,$00d0
    dc.w $100,$1200,$102,0,$104,0,$108,0,$10a,0
    dc.w $180,$012,$182,$fff
copbpl:
    dc.w $0e0,0,$0e2,0
    dc.w $ffff,$fffe
plane: dcb.b 10240,0

Amiga shows the deliberate error row 00 00 01 00 03 0A 14 14. — The wrong client completes with 00 00 01 00 03 0A 14 14; its changed inputs and state explain the result.

Cost and alternatives

The measured helper extent is 330 code bytes; public state is 21 bytes and private scratch is 2 bytes. There are no immutable helper tables. Caller data, the test cases, return-address stack, alignment and display buffers cost additional space. These are assembled sizes, not cycle measurements.

At most eight comparisons. Sorted binary search lowers comparisons for larger immutable tables; direct 256-entry indexing trades ROM for constant lookup.

This is a linear byte-key dictionary, not a text parser or a hash table. The dictionary is read-only during service.

Execution evidence

Four variants run on A500 OCS PAL, Kickstart1.3 OFS cold boot, using Asm198x 0.0.72, Emu198x 0.44.2 and Build198x 0.2.9. Each executes 47 boundary/varied/error table cases, dirty initialisation and the separate retained-state client. An independent mathematical/container model checks every public byte after every call. This is bounded example coverage, not exhaustive correctness for every possible state.

The records retain loaded immutable code, completion, register sentinels, full packets, source/tool/firmware hashes and captures. The public gate validates these retained observations and rejects altered evidence; it does not run restricted firmware. No firmware is distributed. The eight displayed bytes are the first eight public fields, zero-padded when shorter; the packet includes every field.

Where it fits

Decimal parsing: Parsing converts text to a token; lookup associates that token with game data.

The Craft · Maths for Games · Source and native evidence.