80-Bus News

  

November–December 1983, Volume 2, Issue 6











Page 35 of 67











Dis-assembly of NASCOM ROM BASIC Ver 4.7                PAGE    47

EDD1 AF         OPRND:  XOR     A               ; Get operand routine
EDD2 32AD10             LD      (TYPE),A        ; Set numeric expected
EDD5 CD36E8             CALL    GETCHR          ; Get next character
EDD8 1E24               LD      E,MO            ; ?MO Error
EDDA CAC1E3             JP      Z,ERROR         ; No operand - Error
EDDD DA1AF9             JP      C,ASCTFP        ; Number - Get value
EDE0 CD77E9             CALL    CHKLTR          ; See if a letter
EDE3 D222EE             JP      NC,CONVAR       ; Letter - Find variable
EDE6 FEAC               CP      ZPLUS           ; "+" Token ?
EDE8 CAD1ED             JP      Z,OPRND         ; Yes - Look for operand
EDEB FE2E               CP      "."             ; "." ?
EDED CA1AF9             JP      Z,ASCTFP        ; Yes - Create FP number
EDF0 FEAD               CP      ZMINUS          ; "-" Token ?
EDF2 CA11EE             JP      Z,MINUS         ; Yes - Do minus
EDF5 FE22               CP      '"'             ; Literal string ?
EDF7 CACFF1             JP      Z,QTSTR         ; Get string terminated by '"'
EDFA FEAA               CP      ZNOT            ; "NOT" Token ?
EDFC CA08EF             JP      Z,EVNOT         ; Yes - Eval NOT expression
EDFF FEA7               CP      ZFN             ; "FN" Token ?
EE01 CA33F1             JP      Z,DOFN          ; Yes - Do FN routine
EE04 D6B6               SUB     ZSGN            ; Is it a function?
EE06 D233EE             JP      NC,FNOFST       ; Yes - Evaluate function
EE09 CD56ED     EVLPAR: CALL    OPNPAR          ; Evaluate expression in "()"
EE0C CD90E6             CALL    CHKSYN          ; Make sure ")" follows
EE0F 29                 DEFB    ")"
EE10 C9                 RET

EE11 167D       MINUS:  LD      D,7DH           ; "-" precedence
EE13 CD5DED             CALL    EVAL1           ; Evaluate until prec' break
EE16 2AD010             LD      HL,(NXTOPR)     ; Get next operator address
EE19 E5                 PUSH    HL              ; Save next operator address
EE1A CD3CF8             CALL    INVSGN          ; Negate value
EE1D CD44ED     RETNUM: CALL    TSTNUM          ; Make sure it's a number
EE20 E1                 POP     HL              ; Restore next operator address
EE21 C9                 RET

EE22 CD2DEF     CONVAR: CALL    GETVAR          ; Get variable address to DE
EE25 E5         FRMEVL: PUSH    HL              ; Save code string address
EE26 EB                 EX      DE,HL           ; Variable address to HL
EE27 22E410             LD      (FPREG),HL      ; Save address of variable
EE2A 3AAD10             LD      A,(TYPE)        ; Get type
EE2D B7                 OR      A               ; Numeric?
EE2E CC51F8             CALL    Z,PHLTFP        ; Yes - Move contents to FPREG
EE31 E1                 POP     HL              ; Restore code string address
EE32 C9                 RET
Dis-assembly of NASCOM ROM BASIC Ver 4.7                PAGE    46

ED92 7A         FOPRND: LD      A,D             ; < = > found ?
ED93 B7                 OR      A
ED94 C2A8EE             JP      NZ,TSTRED       ; Yes - Test for reduction
ED97 7E                 LD      A,(HL)          ; Get operator token
ED98 22C510             LD      (CUROPR),HL     ; Save operator address
ED9B D6AC               SUB     ZPLUS           ; Operator or function?
ED9D D8                 RET     C               ; Neither - Exit
ED9E FE07               CP      ZOR+1-ZPLUS     ; Is it + - * / ^ AND OR ?
EDA0 D0                 RET     NC              ; No - Exit
EDA1 5F                 LD      E,A             ; Coded operator
EDA2 3AAD10             LD      A,(TYPE)        ; Get data type
EDA5 3D                 DEC     A               ; FF = numeric , 00 = string
EDA6 B3                 OR      E               ; Combine with coded operator
EDA7 7B                 LD      A,E             ; Get coded operator
EDA8 CA06F3             JP      Z,CONCAT        ; String concatenation
EDAB 07                 RLCA                    ; Times 2
EDAC 83                 ADD     A,E             ; Times 3
EDAD 5F                 LD      E,A             ; To DE (D is 0)
EDAE 21A4E2             LD      HL,PRITAB       ; Precedence table
EDB1 19                 ADD     HL,DE           ; To the operator concerned
EDB2 78                 LD      A,B             ; Last operator precedence
EDB3 56                 LD      D,(HL)          ; Get evaluation precedence
EDB4 BA                 CP      D               ; Compare with eval precedence
EDB5 D0                 RET     NC              ; Exit if higher precedence
EDB6 23                 INC     HL              ; Point to routine address
EDB7 CD44ED             CALL    TSTNUM          ; Make sure it's a number

EDBA C5         STKTHS: PUSH    BC              ; Save last precedence & token
EDBB 0169ED             LD      BC,EVAL3        ; Where to go on prec' break
EDBE C5                 PUSH    BC              ; Save on stack for return
EDBF 43                 LD      B,E             ; Save operator
EDC0 4A                 LD      C,D             ; Save precedence
EDC1 CD44F8             CALL    STAKFP          ; Move value to stack
EDC4 58                 LD      E,B             ; Restore operator
EDC5 51                 LD      D,C             ; Restore precedence
EDC6 4E                 LD      C,(HL)          ; Get LSB of routine address
EDC7 23                 INC     HL
EDC8 46                 LD      B,(HL)          ; Get MSB of routine address
EDC9 23                 INC     HL
EDCA C5                 PUSH    BC              ; Save routine address
EDCB 2AC510             LD      HL,(CUROPR)     ; Address of current operator
EDCE C35DED             JP      EVAL1           ; Loop until prec' break

This is an OCR’d version of the scanned page and likely contains recognition errors.

NASCOM ROM BASIC source code is available in ASM and LST file format.











Page 35 of 67