Category : Assembly Language Source Code
Archive   : ASM_SUBR.ZIP
Filename : SFP2TFP

;-------------------------sfp2tfp routine begins--------------------------+
; ROUTINE FOR CONVERSION FROM SINGLE PRECISION TO TEMPORARY FLOATING POINT
;
; from BLUEBOOK OF ASSEMBLY ROUTINES FOR IBM PC & XT.
; page : 93
;
; NAME SFP2TFP
;
; FUNCTION: This routine converts from single precision binary floating point
; to temporary binary floating point.
;
; INPUT: Upon entry a number is stored in single precision binary floating
; point form in SFPBUFF. The single precision binary floating point number
; has a 24-bit binary mantissa, a sign bit, and an 8-bit exponent biased by
; 128 (See fig 5-3).
;
; OUTPUT: Upon exit a temporary binary floating point number is stored 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 sign byte,
; and an 16-bit two's complement exponent (See fig 5-2).
;
; REGISTERS USED: AX is modified.
;
; SEGMENTS REFERENCED: Upon entry the data segment must contain the
; storage for the temporary binary floating point number FPTEMP1 and the
; temporary binary floating point number SFPBUFF.
;
; ROUTINES CALLED: None
;
; SPECIAL NOTES: Equates are used to shorten address fields. This is a
; near procedure needed by FPOUT. Include the file FPCEQU_S at assembly.
;
; ROUTINE TO CONVERT FROM SINGLE PRECISION FLOATING POINT TO
; TEMP FLOATING POINT
;
sfp2tfp proc near
;
; clear lower part of mantissa
mov fptemp1w0,0 ; clear word
mov fptemp1w2,0 ; clear word
mov fptemp1w4,0 ; clear word
;
; move rest of mantissa
mov ax,sfpbuffw0 ; low two bytes
mov fptemp1w6,ax ; put in place
;
mov ax,sfpbuffw2 ; 7 hi bits
and ax,07Fh ; remove sign
or ax,0080h ; restore msb
mov fptemp1w8,ax ; put in place
;
; move sign
mov al,sfpbuffb2 ; in upper byte
and al,80h ; just sign bit
mov fptemp1b10,al ; byte 10 of fptemp1
;
;
; move exponent
mov al,sfpbuffb3 ; byte three of sfp
mov ah,0 ; make into a word
sub ax,80h ; remove bias
mov fptemp1w11,ax ; it's 16-bit 2's complement
;
ret ; return
;
sfp2tfp endp
;-------------------------sfp2tfp routine ends---------------------------+