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Annotation of Net2/arch/tahoe/math/kcvtfl.s, revision 1.1

1.1     ! root        1: /*-
        !             2:  * Copyright (c) 1985 The Regents of the University of California.
        !             3:  * All rights reserved.
        !             4:  *
        !             5:  * This code is derived from software contributed to Berkeley by
        !             6:  * Computer Consoles Inc.
        !             7:  *
        !             8:  * Redistribution and use in source and binary forms, with or without
        !             9:  * modification, are permitted provided that the following conditions
        !            10:  * are met:
        !            11:  * 1. Redistributions of source code must retain the above copyright
        !            12:  *    notice, this list of conditions and the following disclaimer.
        !            13:  * 2. Redistributions in binary form must reproduce the above copyright
        !            14:  *    notice, this list of conditions and the following disclaimer in the
        !            15:  *    documentation and/or other materials provided with the distribution.
        !            16:  * 3. All advertising materials mentioning features or use of this software
        !            17:  *    must display the following acknowledgement:
        !            18:  *     This product includes software developed by the University of
        !            19:  *     California, Berkeley and its contributors.
        !            20:  * 4. Neither the name of the University nor the names of its contributors
        !            21:  *    may be used to endorse or promote products derived from this software
        !            22:  *    without specific prior written permission.
        !            23:  *
        !            24:  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
        !            25:  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
        !            26:  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
        !            27:  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
        !            28:  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
        !            29:  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
        !            30:  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
        !            31:  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
        !            32:  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
        !            33:  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
        !            34:  * SUCH DAMAGE.
        !            35:  *
        !            36:  *     @(#)Kcvtfl.s    7.1 (Berkeley) 12/6/90
        !            37:  */
        !            38: 
        !            39: #include "../math/fp.h"
        !            40: #include "../tahoe/SYS.h"
        !            41: 
        !            42:        .text
        !            43: ENTRY(Kcvtfl, R5|R4|R3|R2)
        !            44:        clrl    r1
        !            45:        clrl    r4              # r4 - negative flag.
        !            46:        clrl    r2              # r2 - exponent.
        !            47:        movl    4(fp),r0        # fetch operand.
        !            48:        movl    r0,r5           # need another copy.
        !            49:        jeql    retzero         # return zero.
        !            50:        jgtr    positive
        !            51:        mnegl   r0,r0
        !            52:        jvs     retmin          # return minimum integer.
        !            53:        incl    r4              # remember it was negative.
        !            54:        movl    r0,r5           # remember the negated value.
        !            55:  #
        !            56:  #Compute exponent:
        !            57:  #
        !            58: positive:
        !            59:        ffs     r0,r1
        !            60:        incl    r1
        !            61:        addl2   r1,r2
        !            62:        shrl    r1,r0,r0
        !            63:        jneq    positive        # look for more set bits.
        !            64:  #
        !            65:  #we have the exponent in r2.
        !            66:  #
        !            67:        movl    r5,r0           # r0 will hold the resulting f.p. number.
        !            68:  #
        !            69:  #Shift the fraction part to its proper place:
        !            70:  #
        !            71:        subl3   r2,$HID_POS,r3
        !            72:        jlss    shiftr          # if less then zero we have to shift right.
        !            73:        shll    r3,r0,r0        # else we shift left.
        !            74:        jmp     shifted
        !            75: shiftr:
        !            76:        mnegl   r3,r3
        !            77:        shrl    r3,r0,r0
        !            78: shifted:
        !            79:        andl2   $CLEARHID,r0    # clear the hidden bit.
        !            80:        shal    $EXPSHIFT,r2,r2 # shift the exponent to its proper place.
        !            81:        orl2    $EXPSIGN,r2     # set the exponent sign bit(to bias it).
        !            82:        orl2    r2,r0           # combine exponent & fraction.
        !            83:        bbc     $0,r4,sign_ok   # do we  have to set the sign bit?
        !            84:        orl2    $SIGNBIT,r0     # yes...
        !            85: sign_ok:
        !            86:        ret
        !            87: 
        !            88: retzero:
        !            89:        clrl    r0
        !            90:        ret
        !            91: 
        !            92: retmin:
        !            93:        movl    $0xd0000000,r0
        !            94:        ret

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