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Annotation of Net2/arch/tahoe/math/kdivf.s, revision 1.1.1.1

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:  *     @(#)Kdivf.s     7.1 (Berkeley) 12/6/90
                     37:  */
                     38: 
                     39: #include "../math/fp.h"
                     40: #include "../math/Kfp.h"
                     41: #include "../tahoe/SYS.h"
                     42: 
                     43: #define        HIDDEN  23              # here we count from 0 not from 1 as in fp.h
                     44: 
                     45:        .text
                     46: ENTRY(Kdivf, R9|R8|R7|R6|R5|R4|R3|R2)
                     47:        clrl    r1
                     48:        clrl    r3              # r3 - sign: 0 for positive,1 for negative.
                     49:        movl    4(fp),r0
                     50:        jgeq    1f
                     51:        movl    $1,r3
                     52: 1:     movl    12(fp),r2
                     53:        jgeq    2f
                     54:        bbc     $0,r3,1f        # seconed operand is negative.
                     55:        clrl    r3              # if first was negative, make result positive.
                     56:        jmp     2f
                     57: 1:     movl    $1,r3           # if first was positive, make result negative.
                     58: 2:     andl2   $EXPMASK,r0     # compute first 'pure'exponent.
                     59:        jeql    retz
                     60:        shrl    $EXPSHIFT,r0,r0
                     61:        subl2   $BIAS,r0        
                     62:        andl2   $EXPMASK,r2     # compute seconed 'pure'exponent.
                     63:        jeql    retz2
                     64:        shrl    $EXPSHIFT,r2,r2
                     65:        subl2   $BIAS,r2
                     66:        subl3   r2,r0,r2        # subtruct the exponents.
                     67:        addl2   $BIAS,r2
                     68:        jleq    underf
                     69:                                # normalization can make the exp. smaller.
                     70:  #
                     71:  #     We have the sign in r3,the exponent in r2,now is the time to
                     72:  #     perform the division...
                     73:  #
                     74:        # fetch dividend. (r0)
                     75:        andl3   $(0!(EXPMASK | SIGNBIT)),4(fp),r0
                     76:        orl2    $(0!CLEARHID),r0
                     77:        clrl    r1
                     78:  
                     79:        # fetch divisor : (r6)
                     80:        andl3   $(0!(EXPMASK | SIGNBIT)),12(fp),r6
                     81:        orl2    $(0!CLEARHID),r6
                     82: 
                     83:        shll    $2,r6,r6        # make the divisor bigger so we will not
                     84:                                # get overflow at the divission.
                     85:        ediv    r6,r0,r0,r7     # quo to r0, rem to r7
                     86:        subl2   $6,r2           # to compensate for: normalization (-24),
                     87:                                # ediv (+32), shifting r6 (-2).
                     88:        
                     89: over:
                     90:        pushl   20(fp)
                     91:        callf   $8,_Kfnorm      # we can use fnorm because we have data
                     92:                                # at r1 as well.(sfnorm takes care only 
                     93:                                # of r0).
                     94: sign:
                     95: 1:     bbc     $0,r3,done
                     96:        orl2    $SIGNBIT,r0
                     97: done:  ret
                     98: 
                     99: retz:
                    100:        clrl    r0
                    101:        ret
                    102: 
                    103: retz2: bbc     $31,12(fp),z_div
                    104:        clrl    r0
                    105:        ret
                    106: 
                    107: underf:
                    108:        orl2    $HFS_UNDF,*20(fp)       
                    109:        ret
                    110: z_div:
                    111:        orl2    $HFS_DIVZ,*20(fp)
                    112:        ret

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