FindAIFFChunk

Synopsis

chunkID, chunkSize = FindAIFFChunk(data, chunkID)
D0       D1                        A0    D0

C Prototype

There is no direct C prototype exported for this function. It is called internally from assembly.

Description

Searches for a specific chunk within an IFF/AIFF data structure. If the data starts with a “FORM” header, the function automatically skips past the 12-byte FORM header (4-byte type ID + 4-byte size + 4-byte form type) before beginning the search.

The function iterates through the chunk list using TestAIFFChunk() to validate each chunk and NextIFFChunk() to advance to the next one, until the requested chunk ID is found.

Inputs

• data (A0) — Pointer to the beginning of the IFF/AIFF data in memory.
• chunkID (D0) — The 4-byte chunk identifier to search for (e.g., "BODY", "CMAP").

Result

• chunkID (D0) — The chunk ID of the found chunk.
• chunkSize (D1) — The size of the found chunk data.
• A0 — Points to the found chunk header.
• If the chunk is not found, the condition codes indicate failure (zero flag set).

See Also

• TestAIFFChunk
• NextIFFChunk
• UnPackerILBMBODY
• UnPackerILBMCMAP

Implementation

The original 68020 assembly implementation:

; Rel.3.1 - Apr 11 1994 --- FindAIFFChunk()
_LVOFindAIFFChunk
        move.l  a1,-(sp)
        lea     "FORM",a1
        cmp.l   (a0),a1
        bne.s   FIFF_NoINIT
        addq.l  #8,a0
        addq.l  #4,a0
 
FIFF_NoINIT
        move.l  d0,d1
 
FIFF_CheckLoop
        bsr.s   _LVOTestAIFFChunk
        beq.s   FIFFChunk_Exit
        cmp.l   (a0),d1
        beq.s   FIFF_FindIt
        bsr.s   _LVONextIFFChunk
        bra.s   FIFF_CheckLoop
 
FIFF_FindIt
        movem.l (a0),d0-d1
 
FIFFChunk_Exit
        move.l  (sp)+,a1
        rts