Category : Assembly Language Source Code
Archive   : ASM-SUBR.ZIP
Filename : TFP2SFP

;-------------------------tfp2sfp routine begins--------------------------+
; ROUTINE FOR CONVERSION FROM TEMPORARY TO SINGLE PRECISION
;
; from BLUEBOOK OF ASSEMBLY ROUTINES FOR IBM PC & XT.
; page : 80
;
; NAME TFP2SFP
;
; FUNCTION: This routine conveerts from temporary binary floating point
; to single precision floating point.
;
; INPUT: Upon entry a number is stored in temporary binary floating point
; form in FPTEMP1. The temporary binary floating point number has a 72-bit
; binary mantissa with 8 bits to the left of those for internal use, a
; signal byte, and a 16-bit two's complement binary exponent (See fig 5-2).
;
; OUTPUT: Upon exit a single precision floating point number is stored 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 (See fig 5-3).
;
; REGISTERS USED: AX and DX are modified.
;
; SEGMENTS REFERENCED: Upon entry the data segment must contain the
; messages INTERNAL, OVERFLOW and UNDERFLOW, and storage for the temporary
; binary floating point number FPTEMP1 and the single precision floating
; point number SFPBUFF.
;
; ROUTINES CALLED: STDSPACE, MESSOUT and HEX16OUT
;
; SPECIAL NOTES: Equates are used to shorten address fields. This is a
; near procedure needed by FPIN. Include the file FPCEQU_S at assembly.
;
; ROUTINE TO CONVERT FROM TEMP FLOATING POINT TO SINGLE PRECISION
; FLOATING POINT
;
tfp2sfp proc near
;
; move mantissa
mov ax,fptemp1w4 ; below word
rcl ax,1 ; carry for roundup
mov ax,fptemp1w6 ; low word
adc ax,0 ; low word + carry
mov sfpbuffw0,ax ; put in place
mov dx,ax ; check for zero
;
mov ax,fptemp1w8
or dx,ax ; check this part too
and ax,007Fh ; just bottom 7 bits
mov sfpbuffw2,ax ; put in place
;
; move sign bit
mov al,fptemp1b10 ; byte 10 is sign
and al,80h
or sfpbuffb2,al ; bit 7 is sign
;
; move exponent
mov ax,fptemp1w11 ; 16-bit two's complement exponent
cmp ax,-128 ; too low ?
jl ftp2sfp2 ; error message
cmp ax,127 ; too high ?
jg tfp2sfp3 ; error message
;
add ax,80h ; bias
cmp dx,0 ; was mantissa 0 ?
jne tfp2sfp
mov al,0 ; then -128 exponent
;
tfp2sfp1
mov sfpbuffb3,al ; put biased byte back
;
; normal return
;
; show hex for debugging
lea si,internal ; point to message
call stdmessout ; display message
;
mov dx,sfpbuffw2 ; upper word
call hex16out ; show it
;
mov dx,sfpbuffw0 ; lower word
call hex16out ; show it
;
call stdspace ; skip a space
clc
ret ; return
;
; underflow error
tfp2sfp3:
lea si,underflow ; point to message
jmp tfp2sfp4
;
tfp2sfp4:
call stdmessout ; send message
stc ; set carry
ret ; return
;
tfp2sfp endp
;-------------------------tfp2sfp routine ends---------------------------+