Category : Assembly Language Source Code
Archive   : ASM-SUBR.ZIP
Filename : FPIN

;-------------------------fpin begins--------------------------+
; from BLUEBOOK OF ASSEMBLY ROUTINES FOR IBM PC & XT.
; page : 88
;
; NAME FPIN
;
; ROUTINE FOR CONVERSION FROM EXTERNAL TO INTERNAL FLOATING POINT
;
; FUNCTION: This routine accepts an ASCII decimal floating point number
; from a std input device and converts it to internal binary floating
; point.
;
; INPUT: The characters of the floating point number are received in ASCII
; through a call to a std input routine. The decimal floating point number
; has an optional sign, followed by decimal digits of the mantissa with one
; embedded decimal point. Following the mantissa is an optional exponent
; which starts with the letter 'E', then an optional sign, then a decimal
; number. It is possible to get erroneous results if the number is too
; large or small to be stored as a single precision binary floating point
; number.
;
; OUTPUT: Upon exit a single precision binary floating point number is in
; SFPBUFF. The single precision floating point number has a 24-bit binary
; mantissa, a sign bit, and an 8-bit exponent biased by 128.
;
; REGISTERS USED: No registers are modified.
;
; SEGMENTS REFERENCED: The data segment contains the variables FPTEMP1,
; FPTEMP2, and SFPBUFF.
;
; ROUTINES CALLED: STDIN, FPINDIGT, FPTMUL, FPTDIV and FPTNORM
;
; SPECIAL NOTES: Equates are used to shorten address fields.
;
; ROUTINE TO CONVERT FROM ASCII EXTERNAL TO INTERNAL FLOATING POINT
;
fpin proc far
;
push di ; save registers
push si
push dx
push cx
push ax
;
; clear fp temp1 buffer
lea di,fptemp1 ; point to fptemp1
mov al,0 ; digit = 0
call fpindigt ; store digit
;
; clear the decimal flap and the count
mov decflag,0 ; clear the flag
mov decexp,0 ; clear the decimal exponent
;
; look for the sign
call stdin ; look for sign
cmp al,'-' ; minus ?
jz fpin1 ; store it
cmp al,'+' ; plus ?
jz fpin2 ; ignore it
jmp fpin3 ; anything else is a player
;
fpin1:
; set sign as a negative
mov fptemp1b10,80h ; put sign in place
;
fpin2:
call stdin ; get next digit
;
fpin3:
cmp al,'.' ; check for decimal point
jne fpin4 ; press on if not
;
; set decimal flag
cmp decflag,0 ; decimal flag already set ?
jne fpin5 ; exit if not the first
mov decflag,0FFh ; set it now.
jmp fpin2 ; go back for a digit
;
fpin4:
sub al,30h ; bring down from ASCII
jl fpin5 ; too low ?
cmp al,9
jg fpin5 ; too high ?
jmp fpin6 ; got a digit
;
fpin5:
jmp fpin15 ; end of mantissa
;
; load digit as a floating point number
fpin6:
lea di,fptemp2 ; point to fptemp2
call fpindigt ; put in the digit
;
; multiply result by 10
lea di,fptemp1 ; point to fptemp1
call fptmul ; multiply by 10
;
; pick one with a larger exponent
mov cx,fptemp1w11 ; get sign of fptemp1
sub cx,fptemp2w11 ; subtract sign of fptemp2
je fpin11 ; skip if equal
jg fpin9 ; if exponent fptemp2 is less
;
fpin7:
; shift the bits
sar fptemp1w8,1 ; shift all bits right
rcr fptemp1w6,1 ; carry on
rcr fptemp1w4,1
rcr fptemp1w2,1
rcr fptemp1w0,1
loop fpin8
;
; set the exponent
mov ax,fptemp2w11 ; get exponent of fptemp2
mov fptemp1w11,ax ; put in exponent of fptemp1
;
jmp fpin11 ; done withthis case
;
fpin9:
;
; exponent of fptemp2 is less than exp of fptemp1
;
fpin10:
; shift the bits
sar fptemp2w8,1 ; shift all bits right
rcr fptemp2w6,1 ; carry on
rcr fptemp2w4,1
rcr fptemp2w2,1
rcr fptemp2w0,1
loop fpin10
;
; set the exponent
mov ax,fptemp1w11 ; get exp of fptemp1
mov fptemp2w11,ax ; put in exp of fptemp2
jmp fpin11 ; end of this case
;
fpin11:
;
; add the digit to result
;
mov cx,5 ; for a count of 5 words
lea di,fptemp1 ; di points to fptemp1
lea si,fptemp2 ; si points to fptemp2
clc
;
fpin12:
mov ax,[si] ; get 16-bit digit from fptemp1
inc si ; point to next 16-bit digit
inc si
adc [di],ax ; add to 16-bit digit of fptemp2
inc di ; point to next 16-bit digit
inc di
loop fpin12
;
; normalize
lea di,fptemp1 ; point to fptemp1
call fptnorm ; renormalize it
;
fpin13:
;
; decrement decimal exponent if dec flag is on
cmp deflag,0 ; check decimal flag
je fpin14 ; skip if not set
dec decexp ; dec exponent if set
;
fpin14:
; adjust for the decimal point
add al,30h ; restore ASCII
and al,5Fh ; upper or lower case
cmp al,'E' ; is it E for Exponent ?
jne fpin16
;
; grab exponent
;
call sgnd16in ; get signed decimal exponent
add dexexp,dx ; add it to our current value
;
fpin16:
; check for sign of decimal exponent
mov cx,decexp ; get decimal exponent
cmp cx,0 ; check its sign
jg fpin17 ; if positive
jl fpin18 ; if negative
;
; zero count
jmp fpin20 ; done if exponent is zero
;
; positive decimal exponent
fpin17:
push cx ; save count = decimal exponent
;
; multiply result by 10
lea di,fptemp1 ; point to fptemp1
call fptmul ; multiply by 10
;
; normalize
lea di,fptemp1 ; point to fptemp1
call fptnorm ; renormalize it
;
pop cx ; restore the count
loop fpin17
;
jmp fpin20 ; end of this case
;
fpin18:
; negative count
neg cx ; absolute value of exponent
fpin19:
push cx ; save count
;
; divide mantissa by 10
lea di,fptemp1 ; point to fptemp1
call fptdiv ; divide by 10
;
; normalize
lea di,fptemp1 ; point to fptemp1
call fptnorm ; renormalize it
;
pop cx ; restore count
loop fpin19
;
fpin20:
call tfp2sfp ; convert to single precision
;
pop ax ; restore registers
pop cx
pop dx
pop si
pop di

;
ret ; return
;
fpin endp
;-------------------------fpin ends---------------------------+