DOS-debug

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;--- defines procedures
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;--- PowerOf10
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;--- FloatToBCD
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;--- FloatToStr
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; These are bits in the FP status word.
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FP_LESSTHAN	equ 01h
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FP_EQUALTO	equ 40h
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MAXNUM equ 16
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CONST segment
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;ten	dq 10.0
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;ten16	dq 1.0e16
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;rounder	dq 5.0e10
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iexp = 1
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ten_1 label tbyte
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repeat 15
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	dt @CatStr(1.0e,%iexp)
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	iexp = iexp + 1
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endm
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ten_16 label tbyte
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repeat 15
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	dt @CatStr(1.0e,%iexp)
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	iexp = iexp + 16
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endm
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;--- just the first exponent is necessary for 8-byte doubles
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ten_256 label tbyte
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repeat 19
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	dt @CatStr(1.0e,%iexp)
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	iexp = iexp + 256
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endm
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CONST ends
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;--- called by FloatToStr
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;--- in: ax=exponent
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;--- modifies: bx, cl
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PowerOf10 proc uses si
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	push ax
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	cmp ax, 0		;.IF (SWORD PTR ax < 0)
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	jge @F
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	neg ax
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@@:
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	fld1
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	mov bl, al
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	and bl, 0fh		;bits 0-3
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	je @F
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	mov si,offset ten_1
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	call mul10
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@@:
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	mov bl, al
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	mov cl, 4
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	shr bl, cl		;bits 4-7
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;	and bl, 0fh
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	je @F
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	mov si,offset ten_16
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	call mul10
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@@:
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	mov bl, ah
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	and bl, 1fh		;bits 8-12
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	je @F
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	mov si,offset ten_256
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	call mul10
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@@:
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	pop ax
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	cmp ax, 0		;.IF (SWORD PTR ax < 0)
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	jge @F
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	fdivp st(1), st
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	ret
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@@:
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	fmulp st(1), st
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	ret
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mul10:
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	dec bl
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	push ax
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	mov al,10		; sizeof TBYTE
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	mul bl
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	xchg bx,ax
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	pop ax
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	fld tbyte ptr [bx + si]
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	fmulp st(1), st
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	retn
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PowerOf10 ENDP
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; Convert a floating point register to ASCII.  For internal use.
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; The result always has exactly 18 digits, with zero padding on the
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; left if required.
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;
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; Entry: ST(0) = a number to convert, 0 <= ST(0) < 1E19.
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;        DI = an 18-character buffer.
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; modifies SI,DI,CX,AX
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FloatToBCD PROC
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if FLATSS
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	sub esp, 12
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	mov esi, esp
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else
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	sub sp, 12
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	mov si, sp
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endif
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	; The fbstp instruction converts the top of the stack to a
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	; packed BCD form in ten bytes, with two digits per byte.  The top 
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	; byte has the sign, which we ignore.
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if FLATSS
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	fbstp [esp]
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else
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	fbstp [si]
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endif
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	; Now we need to unpack the BCD to ASCII.
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if FLATSS
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	add esi, 8
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else
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	add si, 8
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endif
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	mov cx, 9
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@@:
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if FLATSS
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	mov al, ss:[esi]	; xxxx xxxx AAAA BBBB
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	dec esi
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else
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	mov al, [si]		; xxxx xxxx AAAA BBBB
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	dec si
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endif
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if 0
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	rol ax, 12			; BBBB xxxx xxxx AAAA
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	rol ah, 4			; xxxx BBBB xxxx AAAA
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	and ax, 0f0fh		; 0000 BBBB 0000 AAAA
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else
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	db 0D4h,10h			; aam 16: 0000 AAAA 0000 BBBB
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	xchg al,ah			; 0000 BBBB 0000 AAAA
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endif
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	add ax, 3030h
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	stosw
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	loop @B
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if FLATSS
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	add esp, 12
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else
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	add sp, 12
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endif
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	ret
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FloatToBCD ENDP
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;
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; Convert a double precision number to a string.
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;
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; Entry:   SI=fpin   = 10-byte double to convert
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;          DI=pszDbl = buffer to hold converted double
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;
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; Exit:    DI = behind converted double
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FloatToStr PROC USES si
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if FLATSS
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_DATA segment
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iExp dw 0
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;mystat dw 0
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;szTemp db 22 dup (0)
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_DATA ends
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else
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LOCAL iExp: WORD
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LOCAL mystat: WORD
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;local szTemp[22]:BYTE
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endif
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;--- Special case zero has been filtered already (fxtract fails for zero).
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;--- Check for a negative number.
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	mov cl,[si+9]
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	test cl, 80h
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	jz @F
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	and byte ptr [si+9], 07fh		; change to positive
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	mov al,'-'						; store a minus sign
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	stosb
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@@:
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;--- load our value onto the stack.
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	fld tbyte ptr [si]
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	fld st
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	mov [si+9], cl	; restore fpin, must be preserved.
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; Compute the closest power of 10 below the number.  We can't get an
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; exact value because of rounding.  We could get close by adding in
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; log10(mantissa), but it still wouldn't be exact.  Since we'll have to
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; check the result anyway, it's silly to waste cycles worrying about
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; the mantissa.
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;
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; The exponent is basically log2(fpin).  Those of you who remember
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; algebra realize that log2(fpin) x log10(2) = log10(fpin), which is
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; what we want.
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	fxtract			; ST=> mantissa, exponent, fpin
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	fstp st			; drop the mantissa
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	fldlg2			; push log10(2)
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	fmulp st(1), st	; ST = log10(fpin), fpin
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	fistp iExp		; ST = fpin
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;--- A 10-byte double can carry almost 19 digits, but fbstp only stores the
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;--- guaranteed 18.  If you're doing 10-byte doubles, change the '16' to '18'.
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	cmp iExp, 18
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	jnc notbelow18
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	fld st			; ST = fpin, fpin
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	frndint			; ST = int(fpin), fpin
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	fcomp st(1)		; ST = fpin, status set
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if RING0
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	fstsw ax
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else
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	fstsw mystat
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	mov ax, mystat
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endif
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	test ah, FP_EQUALTO
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	jz notequal
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;--- We have an integer!  Lucky day.  Go convert it into a temp buffer.
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	push di
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;	lea di, szTemp
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	call FloatToBCD
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	pop di
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	mov ax, MAXNUM+1
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	mov cx, iExp
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	sub ax, cx
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	inc cx
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;	lea si, szTemp
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	mov si, di
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	add si, ax
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;--- The off-by-one order of magnitude problem below can hit us here.  
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;--- We just trim off the possible leading zero.
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	cmp byte ptr [si],'0'
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	jnz @F
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	inc si
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	dec cx
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@@:
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;--- Copy the rest of the converted BCD value to our buffer.
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	rep movsb
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	jmp ftsExit
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notequal:
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notbelow18:
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;--- Have fbstp round to 17 places.
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	mov ax, MAXNUM
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	sub ax, iExp		; adjust exponent to 17
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	call PowerOf10
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; Either we have exactly 17 digits, or we have exactly 16 digits.  We can
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; detect that condition and adjust now.
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	fcom qword ptr [ten_16]
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    ; x0xxxx00 means top of stack > ten16
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    ; x0xxxx01 means top of stack < ten16
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    ; x1xxxx00 means top of stack = ten16
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if RING0
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	fstsw ax
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else
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	fstsw mystat
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	mov ax, mystat
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endif
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	test ah,1
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	jz @F
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	fmul qword ptr [ten_1]
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	dec iExp
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@@:
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;--- Go convert to BCD.
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	push di
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	lea  di, [di+8]
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	call FloatToBCD
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	pop di
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;	lea si, [szTemp+1]		; point to converted buffer
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	lea si, [di+8+1]		; point to converted buffer
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;--- If the exponent is between -15 and 16, we should express this as a number
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;--- without scientific notation.
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	mov cx, [iExp]
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	push cx
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	add cx,MAXNUM-1
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	cmp cx,MAXNUM*2-1
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	pop cx
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	ja fts6		;if scientific notation
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; If the exponent is less than zero, we insert '0.', then -ecx
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; leading zeros, then 16 digits of mantissa.  If the exponent is
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; positive, we copy ecx+1 digits, then a decimal point (maybe), then 
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; the remaining 16-ecx digits.
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	inc cx
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	cmp cx, 0
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	jg @F
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	mov ax,'.0'
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	stosw
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	neg cx
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	mov al, '0'
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	rep stosb
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	mov cx, MAXNUM
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	jmp fts3
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@@:
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	rep movsb
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	mov al,'.'
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	stosb
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	mov cx, MAXNUM
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	sub cx, [iExp]
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fts3:
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	rep movsb
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;--- Trim off trailing zeros.
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@@:
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	cmp byte ptr [di-1],'0'
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	jnz @F
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	dec di
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	jmp @B
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@@:
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;--- If we cleared out all the decimal digits, kill the decimal point, too.
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	cmp byte ptr [di-1], '.'
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	jnz @F
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	dec di
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@@:    
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;--- That's it.
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	jmp ftsExit
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fts6:
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; Now convert this to a standard, usable format.  If needed, a minus
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; sign is already present in the outgoing buffer, and di already points
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; past it.
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	movsb				; copy the first digit
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	mov al,'.'
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	stosb				; plop in a decimal point
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	movsw				; copy four more digits
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	movsw
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	movsw				; copy two more digits
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if 0
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; The printf %g specified trims off trailing zeros here.  I dislike
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; this, so I've disabled it.  Comment out the if 0 and endif if you
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; want this.
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@@:
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	cmp byte ptr [di-1],'0'
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	jz @F
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	dec di
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	jmp @B
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@@:
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endif
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;--- Shove in the exponent.  If you support 10-byte reals, remember to
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;--- allow 4 digits for the exponent.
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	mov ax,'+e'
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	mov dx, [iExp]
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	and dx, dx
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	jns @F
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	neg dx
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	mov ah,'-'
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@@:
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	stosw
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	xchg ax,dx
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	mov si, 10
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	mov cx,4
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@@:
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	xor dx, dx
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	div si
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	push dx
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	loop @B
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	mov cl,4
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@@:
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	pop ax
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	add al,'0'
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	stosb
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	loop @B
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;	add di, 4	; point to terminator
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ftsExit:
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	ret
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FloatToStr ENDP
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