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Annotation of Net2/arch/tahoe/math/kaddf.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:  *     @(#)Kaddf.s     7.1 (Berkeley) 12/6/90
        !            37:  */
        !            38: 
        !            39: #include "../math/fp.h"
        !            40: #include "../tahoe/SYS.h"
        !            41: 
        !            42: /*
        !            43:  * _Kaddf(acc_most,acc_least,op_most,op_least,hfs)
        !            44:  */
        !            45:        .text
        !            46: ENTRY(Kaddf, R10|R9|R8|R7|R6|R5|R4|R3|R2)
        !            47: /*
        !            48:  * see which operand has a greater exponent
        !            49:  * The greater one will be fetched into r0,r1,r2,r3.
        !            50:  * r0,r1 - 'pure' fraction, r2 - exponent, r3 - sign).
        !            51:  * The smaller operand will be fetched into r4,r5,r6,r7.
        !            52:  */
        !            53:        tstl    4(fp)   # handle (a+b) where a and/or b = 0.0
        !            54:        jneq    next
        !            55:        movl    $0,r1
        !            56:        movl    12(fp),r0
        !            57:        ret
        !            58: next:
        !            59:        tstl    12(fp)
        !            60:        jneq    doit
        !            61:        movl    $0,r1
        !            62:        movl    4(fp),r0
        !            63:        ret
        !            64: doit:
        !            65:        andl3   $EXPMASK,4(fp),r0
        !            66:        andl3   $EXPMASK,12(fp),r1
        !            67:        cmpl    r0,r1
        !            68:        jgtr    first_greater
        !            69: 
        !            70:        movl    12(fp),r0       # bigger operand to r0,r1
        !            71:        movl    16(fp),r1
        !            72: 
        !            73:        movl    4(fp),r4        # smaller operand to r4,r5
        !            74:        movl    8(fp),r5
        !            75:        jmp     expo
        !            76: 
        !            77: first_greater:
        !            78:        movl    4(fp),r0        # bigger operand to r0,r1
        !            79:        movl    8(fp),r1
        !            80: 
        !            81:        movl    12(fp),r4       # smaller operand to r4,r5
        !            82:        movl    16(fp),r5
        !            83: 
        !            84: 
        !            85:  #
        !            86:  #compute exponents:
        !            87:  #
        !            88: expo:
        !            89:        andl3   $EXPMASK,r0,r2  # r2 will hold the exponent.
        !            90:        shrl    $EXPSHIFT,r2,r2
        !            91:        andl3   $EXPMASK,r4,r6  # r6 will hold the exponent.
        !            92:        shrl    $EXPSHIFT,r6,r6
        !            93:  #
        !            94:  #compare the exponents:
        !            95:  #
        !            96:        subl3   r6,r2,r8
        !            97:        jeql    signs
        !            98:        cmpl    r8,$MAX_EXP_DIF
        !            99:        jlss    signs
        !           100:        ret                     # return the bigger number.
        !           101:  
        !           102:  #
        !           103:  #remember the signs:
        !           104:  #
        !           105: signs:
        !           106:        clrl    r3
        !           107:        bbc     $31,r0,sign2    # if negative remember it.
        !           108:        incl    r3
        !           109: sign2:
        !           110:        clrl    r7
        !           111:        bbc     $31,r4,frac     # if negative remember it.
        !           112:        incl    r7
        !           113:  #
        !           114:  #compute 'pure' fraction:
        !           115:  #
        !           116: frac:
        !           117:                                # clear the non fraction parts.
        !           118:        andl2   $(0!(EXPMASK | SIGNBIT)),r0
        !           119:                                # add the hidden bit.
        !           120:        orl2    $(0!CLEARHID),r0
        !           121:                                # clear the non fraction parts.
        !           122:        andl2   $(0!(EXPMASK | SIGNBIT)),r4
        !           123:                                # add the hidden bit.
        !           124:        orl2    $(0!CLEARHID),r4
        !           125: 
        !           126:  #
        !           127:  #shift the smaller operand:
        !           128:  #
        !           129:        shrq    r8,r4,r4
        !           130: eql_exps:
        !           131:        cmpl    r3,r7
        !           132:        jeql    add
        !           133:        bbc     $0,r3,negr4r5
        !           134:  #
        !           135:  #negate the pair r0,r1:
        !           136:  #
        !           137:        clrl    r3
        !           138:        mcoml   r1,r1
        !           139:        clrl    r9              # r9 - carry flag.
        !           140:        incl    r1
        !           141:        bcc     comr0
        !           142:        incl    r9              # remember the carry.
        !           143: comr0: mcoml   r0,r0
        !           144:        bbc     $0,r9,add
        !           145:        incl    r0
        !           146: 
        !           147:  #
        !           148:  #add the fractions:
        !           149:  #
        !           150: add:
        !           151:        clrl    r10             # to remember the sign of the result.
        !           152:        addl2   r5,r1
        !           153:        adwc    r4,r0
        !           154:        jgeq    norm            # if positive go to normelize.
        !           155:        incl    r10             # else remember it and negate the result.
        !           156:  #
        !           157:  #negate the pair r0,r1:
        !           158:  #
        !           159:        clrl    r3
        !           160:        mcoml   r1,r1
        !           161:        clrl    r9              # r9 - carry flag.
        !           162:        incl    r1
        !           163:        bcc     comr00
        !           164:        incl    r9              # remember the carry.
        !           165: comr00:        mcoml   r0,r0
        !           166:        bbc     $0,r9,norm
        !           167:        incl    r0
        !           168: norm:  pushl   20(fp)          # addr of returnen exception.
        !           169:        callf   $8,_Kfnorm
        !           170:  
        !           171:  #
        !           172:  #add the sign bit
        !           173:  #
        !           174:        bbs     $0,r10,negative
        !           175:        bbs     $0,r3,negative
        !           176:        ret
        !           177: negative:
        !           178:        orl2    $SIGNBIT,r0
        !           179:        ret
        !           180:  
        !           181:  
        !           182:  #
        !           183:  #negate the pair r4,r5:
        !           184:  #
        !           185: negr4r5:
        !           186:        clrl    r7
        !           187:        mcoml   r5,r5
        !           188:        clrl    r9              # r9 - carry flag.
        !           189:        incl    r5
        !           190:        bcc     comr4
        !           191:        incl    r9              # remember the carry.
        !           192: comr4: mcoml   r4,r4
        !           193:        bbc     $0,r9,add
        !           194:        incl    r4
        !           195:        jmp     add
        !           196:  
        !           197:  
        !           198:        movl    r4,r0           # return the  smaller operand.
        !           199:        movl    r5,r1
        !           200:        ret
        !           201: 

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