Unofficial Name: FindGroupedField
BCALL Address: 8030
Search for a given field within a "group."
- AHL = address (first type byte) to start searching
- DE = field to search for (e.g. 0A10 to search for the calculator ID)
- HL = address of the first data byte (not the first type byte) of the first matching field
- BC = length of the field
- NZ set if not found.
This routine will stop when it reaches any field of a different major field type. Unless you are explicitly searching for a minor-type-1 field, it will also stop when it reaches one.
The behavior of this routine is perhaps best illustrated by an example. Public keys are stored on the certificate page as a series of two fields: an 071 field which contains the key ID (e.g. 0104) and an 073 field which contains the key itself.
So to find a particular public key, you want to first scan through the 071 fields to find the key ID you're looking for. You then want to find the first 073 field following this one, but you want to stop before you get to another 071 field, or any other unrelated field. "Unrelated" in this case means non-major-type-7, since only major-type-7 fields are allowed within the public key block.
Unlike most of the field search routines, this routine calls GetFieldSize after finding the field, so HL points to the first data byte and BC is the length of the field.
Find public key number 0104 (requires Flash write-enabled):
; Find the certificate patch block ld de,0300h B_CALL FindFirstCertificateField ret nz ; Find the public key block (a subfield of the certificate patch block) ld a,7eh ; or 1e, or 3e, depending on model ld de,0700h B_CALL FindSubField ret nz ; Enter the public key block inc hl ld a,7eh B_CALL GetFieldSize ; Find our public key Loop: ld a,7eh ld de,0710h B_CALL FindGroupedField ret nz ; HL -> key number, BC = length thereof ; check if it is 0104 ld a,7eh B_CALL LoadAIndPaged cp 1 jr nz,Skip inc hl dec bc ld a,7eh B_CALL LoadAIndPaged cp 4 jr nz,Skip inc hl dec bc ld a,b or c jr z,Found0104 Skip: add hl,bc jr Loop Found0104: ld a,7eh ld de,0730h B_CALL FindGroupedField ; HL -> modulus; BC = length