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Annotation of 43BSDReno/sys/tahoemath/Kmuld.s, revision 1.1

1.1     ! root        1: /*     Kmuld.s 1.3     86/01/05        */
        !             2: 
        !             3: #include "../tahoemath/fp.h"
        !             4: #include "../tahoemath/Kfp.h"
        !             5: #include "../tahoe/SYS.h"
        !             6: 
        !             7: #define        HIDDEN  23      /* here we count from 0 not from 1 as in fp.h */
        !             8: 
        !             9: /*
        !            10:  * _Kmuld(acc_most,acc_least,op_most,op_least,hfs)
        !            11:  */
        !            12:        .text
        !            13: ENTRY(Kmuld, R9|R8|R7|R6|R5|R4|R3|R2)
        !            14:        clrl    r3              /* r3 - sign: 0 for positive,1 for negative. */
        !            15:        movl    4(fp),r0
        !            16:        jgeq    1f
        !            17:        movl    $1,r3
        !            18: 1:     movl    12(fp),r2
        !            19:        jgeq    2f
        !            20:        bbc     $0,r3,1f        /* seconed operand is negative. */
        !            21:        clrl    r3              /* if first was neg, make result pos */
        !            22:        jmp     2f
        !            23: 1:     movl    $1,r3           /* if first was pos, make result neg */
        !            24: 2:     andl2   $EXPMASK,r0     /* compute first 'pure'exponent. */
        !            25:        jeql    retzero
        !            26:        shrl    $EXPSHIFT,r0,r0
        !            27:        subl2   $BIASP1,r0      
        !            28:        andl2   $EXPMASK,r2     /* compute seconed 'pure'exponent. */
        !            29:        jeql    retzero
        !            30:        shrl    $EXPSHIFT,r2,r2
        !            31:        subl2   $BIASP1,r2
        !            32:        addl2   r0,r2           /* add the exponents. */
        !            33:        addl2   $(BIASP1+2),r2
        !            34:        jleq    underflow
        !            35:        cmpl    r2,$258         /* normalization can make the exp. smaller. */
        !            36:        jgeq    overflow
        !            37:  /*
        !            38:   *    We have the sign in r3,the exponent in r2,now is the time to
        !            39:   *    perform the multiplication...
        !            40:   */
        !            41:        /* fetch first fraction: (r0,r1) */
        !            42:        andl3   $(0!(EXPMASK | SIGNBIT)),4(fp),r0
        !            43:        orl2    $(0!CLEARHID),r0
        !            44:        movl    8(fp),r1
        !            45:        shlq    $7,r0,r0        /* leave the sign bit cleared. */
        !            46:  
        !            47:        /* fetch seconed fraction: (r4,r5) */
        !            48:        andl3   $(0!(EXPMASK | SIGNBIT)),12(fp),r4
        !            49:        orl2    $(0!CLEARHID),r4
        !            50:        movl    16(fp),r5
        !            51:        shlq    $7,r4,r4        /* leave the sign bit cleared. */
        !            52: 
        !            53:        /* in the following lp1 stands for least significant part of operand 1,
        !            54:        *                  lp2 for least significant part of operand 2,
        !            55:        *                  mp1 for most significant part of operand 1,
        !            56:        *                  mp2 for most significant part of operand 2.
        !            57:        */
        !            58:  
        !            59:        clrl    r6
        !            60:        shrl    $1,r1,r1        /* clear the sign bit of the lp1. */
        !            61:        jeql    1f
        !            62:        emul    r1,r4,$0,r6     /* r6,r7 <-- lp1*mp2 */
        !            63:        shlq    $1,r6,r6        /* to compensate for the shift we did to clear the sign bit. */
        !            64: 1:     shrl    $1,r5,r5        /* clear the sign bit of the lp2. */
        !            65:        jeql    1f
        !            66:        emul    r0,r5,$0,r8     /* r8,r9 <-- mp1*lp2 */
        !            67:        shlq    $1,r8,r8
        !            68:        addl2   r9,r7           /* r6,r7 <-- the sum of the products. */
        !            69:        adwc    r8,r6
        !            70: 1:     emul    r0,r4,$0,r0     /* r0,r1 <-- mp1*mp2  */
        !            71:        addl2   r6,r1           /* add the most sig. part of the sum. */
        !            72:        adwc    $0,r0
        !            73:        movl    r0,r4           /* to see how much we realy need to shift. */
        !            74:        movl    $6,r5           /* r5 - shift counter. */
        !            75:        shrl    $7,r4,r4        /* dummy shift. */
        !            76: 1:     bbs     $HIDDEN,r4,realshift
        !            77:        shll    $1,r4,r4
        !            78:        decl    r2              /* update exponent. */
        !            79:        jeql    underflow
        !            80:        decl    r5              /* update shift counter. */
        !            81:        jmp     1b
        !            82: realshift:
        !            83:        shrq    r5,r0,r0
        !            84:        bbc     $0,r1,shiftmore
        !            85:        incl    r1              /* rounding. */
        !            86: shiftmore:
        !            87:        shrq    $1,r0,r0
        !            88: comb:
        !            89:        andl2   $CLEARHID,r0
        !            90:        shll    $EXPSHIFT,r2,r4
        !            91:        orl2    r4,r0
        !            92:        cmpl    r2,$256
        !            93:        jlss    1f
        !            94:        orl2    $HFS_OVF,*20(fp)        
        !            95: sign:
        !            96: 1:     bbc     $0,r3,done
        !            97:        orl2    $SIGNBIT,r0
        !            98: done:  ret
        !            99: 
        !           100: retzero:
        !           101:        clrl    r0
        !           102:        clrl    r1
        !           103:        ret
        !           104: overflow:
        !           105:        orl2    $HFS_OVF,*20(fp)
        !           106:        ret
        !           107: underflow:
        !           108:        orl2    $HFS_UNDF,*20(fp)
        !           109:        ret

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