usr/src/sys/tahoe/math/Kmulf.s

/*      Kmulf.s 1.4     90/12/04        */

#include "../math/fp.h"
#include "../math/Kfp.h"
#include "../tahoe/SYS.h"

#define HIDDEN  23      /* here we count from 0 not from 1 as in fp.h */

/*
 * _Kmulf(acc_most,acc_least,op_most,op_least,hfs)
 */
        .text
ENTRY(Kmulf, R5|R4|R3|R2)
        clrl    r3              /* r3 - sign: 0 for positive,1 for negative. */
        movl    4(fp),r0
        jgeq    1f
        movl    $1,r3
1:      movl    12(fp),r2
        jgeq    2f
        bbc     $0,r3,1f        /* seconed operand is negative. */
        clrl    r3              /* if first was negative, make result positive. */
        jmp     2f
1:      movl    $1,r3           /* if first was positive, make result negative. */
2:      andl2   $EXPMASK,r0     /* compute first 'pure'exponent. */
        jeql    retzero
        shrl    $EXPSHIFT,r0,r0
        subl2   $BIASP1,r0
        andl2   $EXPMASK,r2     /* compute seconed 'pure'exponent. */
        jeql    retzero
        shrl    $EXPSHIFT,r2,r2
        subl2   $BIASP1,r2
        addl2   r0,r2           /* add the exponents. */
        addl2   $(BIASP1+2),r2
        jleq    underflow
        cmpl    r2,$258         /* normalization can make the exp. smaller. */
        jgeq    overflow
 /*
 *      We have the sign in r3,the exponent in r2,now is the time to
 *      perform the multiplication...
 */
        /* fetch first fraction: (r0) */
        andl3   $(0!(EXPMASK | SIGNBIT)),4(fp),r0
        orl2    $(0!CLEARHID),r0
        shll    $7,r0,r0        /* leave the sign bit cleared. */

        /* fetch seconed fraction: (r4) */
        andl3   $(0!(EXPMASK | SIGNBIT)),12(fp),r4
        orl2    $(0!CLEARHID),r4
        shll    $7,r4,r4        /* leave the sign bit cleared. */


        emul    r4,r0,$0,r0
        movl    r0,r4           /* to see how much we realy need to shift. */
        movl    $6,r5           /* r5 - shift counter. */
        shrl    $7,r4,r4        /* dummy shift. */
1:      bbs     $HIDDEN,r4,realshift
        shll    $1,r4,r4
        decl    r2              /* update exponent. */
        jeql    underflow
        decl    r5              /* update shift counter. */
        jmp     1b
realshift:
        shrl    r5,r0,r0
        bbc     $0,r1,shiftmore
        incl    r1              /* rounding. */
shiftmore:
        shrl    $1,r0,r0
comb:
        andl2   $CLEARHID,r0
        shll    $EXPSHIFT,r2,r4
        orl2    r4,r0
        cmpl    r2,$256
        jlss    1f
        orl2    $HFS_OVF,*20(fp)
sign:
1:      bbc     $0,r3,done
        orl2    $SIGNBIT,r0
done:   ret


  retzero:
          clrl  r0
          ret
  overflow:
        orl2    $HFS_OVF,*20(fp)
        jmp     sign
  underflow:
        orl2    $HFS_UNDF,*20(fp)
        ret