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bin32.asm
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Assembly Source File
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1986-01-17
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4KB
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85 lines
BIN32 PROC NEAR
;*************************************************************
; converts an ASCII decimal string to a
; signed 32-bit binary integer in DX:AX
; input--DI points to end of string
; SI points to start
; output--CX if negative, number of digits
; right of decimal point
; SI points to next unconverted char
;*************************************************************
PUSH BP
SUB DX,DX
; get sign
MOV CX,DX ;assume positive sign
MOV AL,[SI] ;put first char in AL
CMP AL," " ;is it blank? positive sign
JE BIN32A
CMP AL,"+" ;is it plus sign?
JE BIN32A
CMP AL,"-" ;is it minus sign?
JNE BIN32B
DEC CX ;sign negative-set flag inCX
BIN32A: INC SI ;point to next char
BIN32B: PUSH CX ;save sign
; convert string
MOV AX,DX ;0-initial NUMber in DX:AX
MOV CL,127 ;max 127 places left of decimal
;CL=COUNT places right ofdecimal
; get ASCII digit
BIN32C: MOV CH,[SI] ;next char in CH
CMP CH,"9" ;if CH > "9" not a digit
JA BIN32H
SUB CH,48 ;convert to binary
JB BIN32H ;if CH < "0" not a digit
DEC CL ;found digit--decrement COUNT
; multiply NUM * 10
MOV BP,CX ;save CX in BP
SUB CX,CX ;decimal 10 in CX:BX
MOV BX,10
CALL MUL32 ;MUL32 returns DX:AX:CX:BX
; check for overflow--over 2^31-1
OR AX,AX ;if AL not zero, product ▄j ▄î JNZ BIN32I ;is > or = 2^32-overflow
OR CX,CX ;if CX sign bit set, product
JS BIN32I ;is > or = 2^31-overflow
; add in this digit
XCHG CX,BP ;digit & COUNT in CX
MOV AL,CH ;this digit in DX:AX
ADD AX,BX ;add NUM*10 from CX:BX
ADC DX,BP
JC BIN32I ;check for overflow again
; get next ASCII character
BIN32D: INC SI ;point to next char
CMP SI,DI ;is there another one?
JB BIN32C ;if so, go get it
; set final decimal place count
BIN32E: XCHG AX,CX ;convert count in CL
CBW ;to word in AX
XCHG AX,CX ;put count back in CX
OR CX,CX ;there are no decimals
JS BIN32F ;if count in CX is positive,
SUB CX,CX ;so make CX zero
; restore sign
BIN32F: POP BX
OR BX,BX
JNS BIN32G ;if sign was negative
NOT AX ;negate NUM
NOT DX
ADD AX,1
ADC DX,0
; wrap up
BIN32G: SUB BX,BX ;BX=0 status ok
POP BP
RET
; found non-numeric character
BIN32H: CMP CH,-2 ;is it decimal point (46-48)?
JNE BIN32E ;if not, finish
SUB CL,CL ;decimal so,set COUNT tozero
JMP BIN32D ;and get next char
; overflow
BIN32I: POP BX ;remove sign from stack
POP BP ;restore BP
MOV BX,1 ;BX=1 overflow flag
RET
BIN32 ENDP