80-Bus News


November–December 1983 · Volume 2 · Issue 6

Page 37 of 67
Dis-assembly of NASCOM ROM BASIC Ver 4.7                PAGE    50

EEBA BCEE       CMPLOG: DEFW    CMPLG1          ; Compare two values / strings
EEBC 79         CMPLG1: LD      A,C             ; Get data type
EEBD B7                 OR      A
EEBE 1F                 RRA
EEBF C1                 POP     BC              ; Get last expression to BCDE
EEC0 D1                 POP     DE
EEC1 F5                 PUSH    AF              ; Save status
EEC2 CD46ED             CALL    CHKTYP          ; Check that types match
EEC5 21FEEE             LD      HL,CMPRES       ; Result to comparison
EEC8 E5                 PUSH    HL              ; Save for RETurn
EEC9 CA8EF8             JP      Z,CMPNUM        ; Compare values if numeric
EECC AF                 XOR     A               ; Compare two strings
EECD 32AD10             LD      (TYPE),A        ; Set type to numeric
EED0 D5                 PUSH    DE              ; Save string name
EED1 CD53F3             CALL    GSTRCU          ; Get current string
EED4 7E                 LD      A,(HL)          ; Get length of string
EED5 23                 INC     HL
EED6 23                 INC     HL
EED7 4E                 LD      C,(HL)          ; Get LSB of address
EED8 23                 INC     HL
EED9 46                 LD      B,(HL)          ; Get MSB of address
EEDA D1                 POP     DE              ; Restore string name
EEDB C5                 PUSH    BC              ; Save address of string
EEDC F5                 PUSH    AF              ; Save length of string
EEDD CD57F3             CALL    GSTRDE          ; Get second string
EEE0 CD62F8             CALL    LOADFP          ; Get address of second string
EEE3 F1                 POP     AF              ; Restore length of string 1
EEE4 57                 LD      D,A             ; Length to D
EEE5 E1                 POP     HL              ; Restore address of string 1
EEE6 7B         CMPSTR: LD      A,E             ; Bytes of string 2 to do
EEE7 B2                 OR      D               ; Bytes of string 1 to do
EEE8 C8                 RET     Z               ; Exit if all bytes compared
EEE9 7A                 LD      A,D             ; Get bytes of string 1 to do
EEEA D601               SUB     1
EEEC D8                 RET     C               ; Exit if end of string 1
EEED AF                 XOR     A
EEEE BB                 CP      E               ; Bytes of string 2 to do
EEEF 3C                 INC     A
EEF0 D0                 RET     NC              ; Exit if end of string 2
EEF1 15                 DEC     D               ; Count bytes in string 1
EEF2 1D                 DEC     E               ; Count bytes in string 2
EEF3 0A                 LD      A,(BC)          ; Byte in string 2
EEF4 BE                 CP      (HL)            ; Compare to byte in string 1
EEF5 23                 INC     HL              ; Move up string 1
EEF6 03                 INC     BC              ; Move up string 2
EEF7 CAE6EE             JP      Z,CMPSTR        ; Same - Try next bytes
EEFA 3F                 CCF                     ; Flag difference (">" or "<")
EEFB C31EF8             JP      FLGDIF          ; "<" gives -1 , ">" gives +1

EEFE 3C         CMPRES: INC     A               ; Increment current value
EEFF 8F                 ADC     A,A             ; Double plus carry
EF00 C1                 POP     BC              ; Get other value
EF01 A0                 AND     B               ; Combine them
EF02 C6FF               ADD     A,-1            ; Carry set if different
EF04 9F                 SBC     A,A             ; 00 - Equal , FF - Different
EF05 C325F8             JP      FLGREL          ; Set current value & continue
Dis-assembly of NASCOM ROM BASIC Ver 4.7                PAGE    51

EF08 165A       EVNOT:  LD      D,5AH           ; Precedence value for "NOT"
EF0A CD5DED             CALL    EVAL1           ; Eval until precedence break
EF0D CD44ED             CALL    TSTNUM          ; Make sure it's a number
EF10 CD8BE9             CALL    DEINT           ; Get integer -32768 - 32767
EF13 7B                 LD      A,E             ; Get LSB
EF14 2F                 CPL                     ; Invert LSB
EF15 4F                 LD      C,A             ; Save "NOT" of LSB
EF16 7A                 LD      A,D             ; Get MSB
EF17 2F                 CPL                     ; Invert MSB
EF18 CDF1F0             CALL    ACPASS          ; Save AC as current
EF1B C1                 POP     BC              ; Clean up stack
EF1C C369ED             JP      EVAL3           ; Continue evaluation

EF1F 2B         DIMRET: DEC     HL              ; DEC 'cos GETCHR INCs
EF20 CD36E8             CALL    GETCHR          ; Get next character
EF23 C8                 RET     Z               ; End of DIM statement
EF24 CD90E6             CALL    CHKSYN          ; Make sure "," follows
EF27 2C                 DEFB    ","
EF28 011FEF     DIM:    LD      BC,DIMRET       ; Return to "DIMRET"
EF2B C5                 PUSH    BC              ; Save on stack
EF2C F6                 DEFB    (OR n)          ; Flag "Create" variable
EF2D AF         GETVAR: XOR     A               ; Find variable address,to DE
EF2E 32AC10             LD      (LCRFLG),A      ; Set locate / create flag
EF31 46                 LD      B,(HL)          ; Get First byte of name
EF32 CD77E9     GTFNAM: CALL    CHKLTR          ; See if a letter
EF35 DAADE3             JP      C,SNERR         ; ?SN Error if not a letter
EF38 AF                 XOR     A
EF39 4F                 LD      C,A             ; Clear second byte of name
EF3A 32AD10             LD      (TYPE),A        ; Set type to numeric
EF3D CD36E8             CALL    GETCHR          ; Get next character
EF40 DA49EF             JP      C,SVNAM2        ; Numeric - Save in name
EF43 CD77E9             CALL    CHKLTR          ; See if a letter
EF46 DA56EF             JP      C,CHARTY        ; Not a letter - Check type
EF49 4F         SVNAM2: LD      C,A             ; Save second byte of name
EF4A CD36E8     ENDNAM: CALL    GETCHR          ; Get next character
EF4D DA4AEF             JP      C,ENDNAM        ; Numeric - Get another
EF50 CD77E9             CALL    CHKLTR          ; See if a letter
EF53 D24AEF             JP      NC,ENDNAM       ; Letter - Get another
EF56 D624       CHARTY: SUB     "$"             ; String variable?
EF58 C265EF             JP      NZ,NOTSTR       ; No - Numeric variable
EF5B 3C                 INC     A               ; A = 1 (string type)
EF5C 32AD10             LD      (TYPE),A        ; Set type to string
EF5F 0F                 RRCA                    ; A = 80H , Flag for string
EF60 81                 ADD     A,C             ; 2nd byte of name has bit 7 on
EF61 4F                 LD      C,A             ; Resave second byte on name
EF62 CD36E8             CALL    GETCHR          ; Get next character
EF65 3ACB10     NOTSTR: LD      A,(FORFLG)      ; Array name needed ?
EF68 3D                 DEC     A
EF69 CA12F0             JP      Z,ARLDSV        ; Yes - Get array name
EF6C F275EF             JP      P,NSCFOR        ; No array with "FOR" or "FN"
EF6F 7E                 LD      A,(HL)          ; Get byte again
EF70 D628               SUB     "("             ; Subscripted variable?
EF72 CAEAEF             JP      Z,SBSCPT        ; Yes - Sort out subscript

NASCOM ROM BASIC dis-assembled is available in ASM and LST file format.

Page 37 of 67