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/*
* expandsf.s
*
* Expands a single float into a flag byte, a sign byte, an exponent,
* and a mantissa.
*
* The contents of this file are subject to the Mozilla Public License
* Version 1.0 (the "License"); you may not use this file except in
* compliance with the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS"
* basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the
* License for the specific language governing rights and limitations
* under the License.
*
* The Original Code is Librcx floating point code, released May 27, 1999.
*
* The Initial Developer of the Original Code is Kekoa Proudfoot.
* Portions created by Kekoa Proudfoot are Copyright (C) 1999
* Kekoa Proudfoot. All Rights Reserved.
*
* Contributor(s): Kekoa Proudfoot <kekoa@graphics.stanford.edu>
*/
.section .text
;;
;; function: expandsf
;; input: float in r5r6
;; output: flags in r3h, sign in r3l, exp in r4, mant in r5r6
;; flag bits: 0=zero, 1=inf, 2=nan
;;
.global ___expandsf
___expandsf:
; Clear flag byte
sub.b r3h,r3h ; clear flags (r3h)
; Extract sign (to r3l)
mov.b r5h,r3l ; extract byte
and.b #0x80,r3l ; mask to get sign bit
; Extract exponent (to r4)
sub.w r4,r4 ; clear exponent (r4)
mov.b r5h,r4l ; copy upper 7 bits of exponent from r5h
bld #7,r5l ; load lsb to carry (lsb is msb of r5l)
rotxl.b r4l ; rotate to align
; Clear upper mantissa bit (mantissa is in r5l r6h r6l)
bclr #7,r5l ; clear upper bit of second mantissa byte
; Upper byte of mantissa (r5h) as a temporary, for now
; Set it to non-zero if mantissa (r5l r6h r6l) is non-zero
mov.b r5l,r5h ; set temp (r5h) non-zero if mantissa non-zero
or.b r6h,r5h
or.b r6l,r5h
; Is the exponent non-zero? Note r4h is known to be zero.
mov.b r4l,r4l ; if exponent (r4l) non-zero
beq else_0
; Does the exponent indicate infinity or NaN? Note r4h is zero.
cmp.b #0xff,r4l ; if exponent (r4l) is ff
bne endif_1
; Set the infinity flag if the mantissa is zero
; Set the NaN flag if the mantissa is non-zero
; Use temp in r5h to see if mantissa is zero or not
add.b #0xff,r5h ; set carry if temp non-zero (destroying temp)
bist #1,r3h ; set inf flag to ~carry (mantissa zero)
bst #2,r3h ; set nan flag to carry (mantissa non-zero)
; Make exponent huge so it dominates finites
; Simplifies e.g. adding finite to inf or dividing inf by finite
mov.b #0x01,r4h ; set lsb of upper exponent byte
endif_1:
; Set the hidden one bit in the mantissa
bset #7,r5l ; set hidden one bit
bra endif_0
else_0:
; Exponent is zero.
; Is the mantissa non-zero, indicating a denorm?
; Use temp in r5h to see if mantissa is zero or not
mov.b r5h,r5h ; if mantissa is non-zero
beq else_2
; Set the exponent to 1, its true value
mov.b #0x01,r4l ; set exponent (r4l) to one
; Normalize the mantissa
; Do/while appropriate because must shift left at least one place
dowhile_3:
; Shift mantissa one place to left
add.w r6,r6 ; shift mantissa left 1 place by adding
addx.b r5l,r5l ; note only 3 significant bytes
; Decrement exponent
subs #1,r4
; Is one bit set? (one bit is in 1 << 23 or 00800000 position)
btst #7,r5l ; check 00800000 bit of mantissa
beq dowhile_3 ; zero indicates bit not set yet
bra endif_2
else_2:
; Mantissa is zero, indicating a zero value
; Set the zero flag
bset #0,r3h ; set zero flag
endif_2:
endif_0:
; Clear the upper mantissa byte, which we used as a temporary
sub.b r5h,r5h ; clear upper mantissa byte
rts
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