80-Bus News

  

March–April 1984, Volume 3, Issue 2











Page 23 of 51











NASCOM
ROM
BASIC
DIS–ASSEMBLED

PART 6

BY CARL LLOYD–PARKER


Dis-assembly of NASCOM ROM BASIC Ver 4.7                PAGE    77

F75B CD44F8     DIV10:  CALL    STAKFP          ; Save FPREG on stack
F75E 012084             LD      BC,8420H        ; BCDE = 10.
F761 110000             LD      DE,0000H
F764 CD54F8             CALL    FPBCDE          ; Move 10 to FPREG

F767 C1         DIV:    POP     BC              ; Get number from stack
F768 D1                 POP     DE
F769 CD13F8     DVBCDE: CALL    TSTSGN          ; Test sign of FPREG
F76C CAB0E3             JP      Z,DZERR         ; Error if division by zero
F76F 2EFF               LD      L,-1            ; Flag subtract exponents
F771 CDD1F7             CALL    ADDEXP          ; Subtract exponents
F774 34                 INC     (HL)            ; Add 2 to exponent to adjust
F775 34                 INC     (HL)
F776 2B                 DEC     HL              ; Point to MSB
F777 7E                 LD      A,(HL)          ; Get MSB of dividend
F778 321210             LD      (DIV3),A        ; Save for subtraction
F77B 2B                 DEC     HL
F77C 7E                 LD      A,(HL)          ; Get NMSB of dividend
F77D 320E10             LD      (DIV2),A        ; Save for subtraction
F780 2B                 DEC     HL
F781 7E                 LD      A,(HL)          ; Get MSB of dividend
F782 320A10             LD      (DIV1),A        ; Save for subtraction
F785 41                 LD      B,C             ; Get MSB
F786 EB                 EX      DE,HL           ; NMSB,LSB to HL
F787 AF                 XOR     A
F788 4F                 LD      C,A             ; Clear MSB of quotient
F789 57                 LD      D,A             ; Clear NMSB of quotient
F78A 5F                 LD      E,A             ; Clear LSB of quotient
F78B 321510             LD      (DIV4),A        ; Clear overflow count
F78E E5         DIVLP:  PUSH    HL              ; Save divisor
F78F C5                 PUSH    BC
F790 7D                 LD      A,L             ; Get LSB of number
F791 CD0910             CALL    DIVSUP          ; Subt' divisor from dividend
F794 DE00               SBC     A,0             ; Count for overflows
F796 3F                 CCF
F797 D2A1F7             JP      NC,RESDIV       ; Restore divisor if borrow
F79A 321510             LD      (DIV4),A        ; Re-save overflow count
F79D F1                 POP     AF              ; Scrap divisor
F79E F1                 POP     AF
F79F 37                 SCF                     ; Set carry to
F7A0 D2                 DEFB    (JP NC,nn)      ; Skip "POP BC" and "POP HL"

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











Page 23 of 51