80-Bus News


January–February 1984, Volume 3, Issue 1

Page 32 of 55

Dis-assembly of NASCOM ROM BASIC Ver 4.7                PAGE    71

F56B 219DF5     OUTBAD: LD      HL,BAD          ; "Bad" message
F56E CD10F2             CALL    PRS             ; Output string
F571 C3E1E3             JP      ERRIN           ; In line message

F574 C5         FILFND: PUSH    BC              ; <- Save
F575 E5                 PUSH    HL              ; <- all
F576 D5                 PUSH    DE              ; <- the
F577 F5                 PUSH    AF              ; <- registers
F578 218EF5             LD      HL,FILE         ; "File" message
F57B CD10F2             CALL    PRS             ; Output string
F57E F1                 POP     AF              ; Get file name
F57F F5                 PUSH    AF              ; And re-save
F580 CDD9FC             CALL    CONMON          ; Output file name to screen
F583 2194F5             LD      HL,FOUND        ; "Found" message
F586 CD10F2             CALL    PRS             ; Output string
F589 F1                 POP     AF              ; <- Restore
F58A D1                 POP     DE              ; <- all
F58B E1                 POP     HL              ; <- the
F58C C1                 POP     BC              ; <- registers
F58D C9                 RET

F58E 46696C65   FILE:   DEFB    "File ",0
F594 20466F75   FOUND:  DEFB    " Found",CR,LF,0
F59D 42616400   BAD:    DEFB    "Bad",0,0,0

F5A3 CD8BE9     PEEK:   CALL    DEINT           ; Get memory address
F5A6 1A                 LD      A,(DE)          ; Get byte in memory
F5A7 C301F1             JP      PASSA           ; Return integer A

F5AA CD41ED     POKE:   CALL    GETNUM          ; Get memory address
F5AD CD8BE9             CALL    DEINT           ; Get integer -32768 to 3276
F5B0 D5                 PUSH    DE              ; Save memory address
F5B1 CD90E6             CALL    CHKSYN          ; Make sure "," follows
F5B4 2C                 DEFB    ","
F5B5 CD84F4             CALL    GETINT          ; Get integer 0-255
F5B8 D1                 POP     DE              ; Restore memory address
F5B9 12                 LD      (DE),A          ; Load it into memory
F5BA C9                 RET

F5BB 2191FA     ROUND:  LD      HL,HALF         ; Add 0.5 to FPREG
F5BE CD62F8     ADDPHL: CALL    LOADFP          ; Load FP at (HL) to BCDE
F5C1 C3CDF5             JP      FPADD           ; Add BCDE to FPREG
Dis-assembly of NASCOM ROM BASIC Ver 4.7                PAGE    72

F5C4 CD62F8     SUBPHL: CALL    LOADFP          ; FPREG = -FPREG + number at HL
F5C7 21                 DEFB    (LD HL,nn)      ; Skip "POP BC" and "POP DE"
F5C8 C1         PSUB:   POP     BC              ; Get FP number from stack
F5C9 D1                 POP     DE
F5CA CD3CF8     SUBCDE: CALL    INVSGN          ; Negate FPREG
F5CD 78         FPADD:  LD      A,B             ; Get FP exponent
F5CE B7                 OR      A               ; Is number zero?
F5CF C8                 RET     Z               ; Yes - Nothing to add
F5D0 3AE710             LD      A,(FPEXP)       ; Get FPREG exponent
F5D3 B7                 OR      A               ; Is this number zero?
F5D4 CA54F8             JP      Z,FPBCDE        ; Yes - Move BCDE to FPREG
F5D7 90                 SUB     B               ; BCDE number larger?
F5D8 D2E7F5             JP      NC,NOSWAP       ; No - Don't swap them
F5DB 2F                 CPL                     ; Two's complement
F5DC 3C                 INC     A               ;  FP exponent
F5DD EB                 EX      DE,HL
F5DE CD44F8             CALL    STAKFP          ; Put FPREG on stack
F5E1 EB                 EX      DE,HL
F5E2 CD54F8             CALL    FPBCDE          ; Move BCDE to FPREG
F5E5 C1                 POP     BC              ; Restore number from stack
F5E6 D1                 POP     DE
F5E7 FE19       NOSWAP: CP      24+1            ; Second number insignificant?
F5E9 D0                 RET     NC              ; Yes - First number is result
F5EA F5                 PUSH    AF              ; Save number of bits to scale
F5EB CD79F8             CALL    SIGNS           ; Set MSBs & sign of result
F5EE 67                 LD      H,A             ; Save sign of result
F5EF F1                 POP     AF              ; Restore scaling factor
F5F0 CD92F6             CALL    SCALE           ; Scale BCDE to same exponent
F5F3 B4                 OR      H               ; Result to be positive?
F5F4 21E410             LD      HL,FPREG        ; Point to FPREG
F5F7 F20DF6             JP      P,MINCDE        ; No - Subtract FPREG from CDE
F5FA CD72F6             CALL    PLUCDE          ; Add FPREG to CDE
F5FD D253F6             JP      NC,RONDUP       ; No overflow - Round it up
F600 23                 INC     HL              ; Point to exponent
F601 34                 INC     (HL)            ; Increment it
F602 CABCE3             JP      Z,OVERR         ; Number overflowed - Error
F605 2E01               LD      L,1             ; 1 bit to shift right
F607 CDA8F6             CALL    SHRT1           ; Shift result right
F60A C353F6             JP      RONDUP          ; Round it up

F60D AF         MINCDE: XOR     A               ; Clear A and carry
F60E 90                 SUB     B               ; Negate exponent
F60F 47                 LD      B,A             ; Re-save exponent
F610 7E                 LD      A,(HL)          ; Get LSB of FPREG
F611 9B                 SBC     A, E            ; Subtract LSB of BCDE
F612 5F                 LD      E,A             ; Save LSB of BCDE
F613 23                 INC     HL
F614 7E                 LD      A,(HL)          ; Get NMSB of FPREG
F615 9A                 SBC     A,D             ; Subtract NMSB of BCDE
F616 57                 LD      D,A             ; Save NMSB of BCDE
F617 23                 INC     HL
F618 7E                 LD      A,(HL)          ; Get MSB of FPREG
F619 99                 SBC     A,C             ; Subtract MSB of BCDE
F61A 4F                 LD      C,A             ; Save MSB of BCDE
F61B DC7EF6     CONPOS: CALL    C,COMPL         ; Overflow - Make it positive

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 32 of 55