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

;-------------------------float routine begins--------------------------+
; from BLUEBOOK OF ASSEMBLY ROUTINES FOR IBM PC & XT.
; page : 109
;
; NAME FLOAT
;
; ROUTINE FOR Conversion from 16-Bit Integer to Floating Point
;
; FUNCTION: This routine converts an unsigned 16-bit binary number to a
; single precision binary floating point number.
;
; INPUT: Upon entry DX contains an unsigned 16-bit binary number
;
; OUTPUT: Upon exit SFPBUFF contains a single precision floating point
; number. 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. DX is used for input.
;
; SEGMENTS REFERENCED: The data segment contains storage for the variable
; SFPBUFF and the message INTERNAL.
;
; ROUTINES CALLED: STDMESSOUT, HEX16OUT, STDSPACE (All for debugging).
;
; SPECIAL NOTES: Equates are used to shorten address fields.
;
; ROUTINE TO CONVERT FROM INTERNAL INTEGER TO INTERNAL FLOATING POINT
;
float proc far
;
; the number is in DX
;
push dx ; save registers
push cx
push ax
;
mov ax,0 ; extend to 32 bits
cmp dx,0 ; check if zero
jz float4
;
float1:
mox cx,9800h ; initialize exponent and sign
; shift left until normalized
;
float2:
test ax,0080h ; done yet ?
jnz float3 ; exit if true
sal dx,1 ; shift all bits left if not
rcl ax,1 ; carry on
dec ch ; decrement the exponent
jmp float2
;
float3:
;
; pack it in
and ax,007Fh ; just the mantissa
or ax,cx ; exponent and sign
;
float4:
mov sfpbuffw0,dx ; put lower part into place
mov sfpbuffw2,ax ; put upper part into place
;
; show hex for debugging
lea si,internal ; point to message
call stdmessout ; send message
;
mov dx,sfpbuffw2 ; upper word
call hex16out ; show it
;
call stdspace ; skip space
;
pop ax ; restore registers
pop cx
pop dx
ret ; return
;
float endp
;-------------------------float routine ends---------------------------+