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

/*      Kmuld.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 */

/*
 * _Kmuld(acc_most,acc_least,op_most,op_least,hfs)
 */
        .text
ENTRY(Kmuld, R9|R8|R7|R6|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 neg, make result pos */
        jmp     2f
1:      movl    $1,r3           /* if first was pos, make result neg */
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,r1) */
        andl3   $(0!(EXPMASK | SIGNBIT)),4(fp),r0
        orl2    $(0!CLEARHID),r0
        movl    8(fp),r1
        shlq    $7,r0,r0        /* leave the sign bit cleared. */

        /* fetch seconed fraction: (r4,r5) */
        andl3   $(0!(EXPMASK | SIGNBIT)),12(fp),r4
        orl2    $(0!CLEARHID),r4
        movl    16(fp),r5
        shlq    $7,r4,r4        /* leave the sign bit cleared. */

        /* in the following lp1 stands for least significant part of operand 1,
        *                  lp2 for least significant part of operand 2,
        *                  mp1 for most significant part of operand 1,
        *                  mp2 for most significant part of operand 2.
        */

        clrl    r6
        shrl    $1,r1,r1        /* clear the sign bit of the lp1. */
        jeql    1f
        emul    r1,r4,$0,r6     /* r6,r7 <-- lp1*mp2 */
        shlq    $1,r6,r6        /* to compensate for the shift we did to clear the sign bit. */
1:      shrl    $1,r5,r5        /* clear the sign bit of the lp2. */
        jeql    1f
        emul    r0,r5,$0,r8     /* r8,r9 <-- mp1*lp2 */
        shlq    $1,r8,r8
        addl2   r9,r7           /* r6,r7 <-- the sum of the products. */
        adwc    r8,r6
1:      emul    r0,r4,$0,r0     /* r0,r1 <-- mp1*mp2  */
        addl2   r6,r1           /* add the most sig. part of the sum. */
        adwc    $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:
        shrq    r5,r0,r0
        bbc     $0,r1,shiftmore
        incl    r1              /* rounding. */
shiftmore:
        shrq    $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
        clrl    r1
        ret
overflow:
        orl2    $HFS_OVF,*20(fp)
        ret
underflow:
        orl2    $HFS_UNDF,*20(fp)
        ret