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Annotation of researchv10no/sys/ml/udiv.s, revision 1.1

1.1     ! root        1: #
        !             2: #      udiv - unsigned division for vax-11
        !             3: #
        !             4: #      arguments: dividend, divisor.
        !             5: #      result: quotient.
        !             6: #      uses r0-r2
        !             7: #
        !             8: #      If 1 < divisor <= 2147483647, zero-extend the dividend
        !             9: #      to 64 bits and let ediv do the work.  If the divisor is 1,
        !            10: #      ediv will overflow if bit 31 of the dividend is on, so
        !            11: #      just return the dividend unchanged.  If the divisor is 0,
        !            12: #      do the ediv also, so it will generate the proper exception.
        !            13: #      All other values of the divisor have bit 31 on: in this case
        !            14: #      the quotient must be 0 if divisor > dividend, and 1 otherwise,
        !            15: #      provided that the comparison is made as unsigned.
        !            16: #
        !            17:        .text
        !            18:        .align  1
        !            19:        .globl  udiv
        !            20: udiv:  .word   0x0000
        !            21:        movl    4(ap),r0        # Dividend
        !            22:        movl    8(ap),r2        # Divisor
        !            23:        jeql    1f              # If divisor=0, force exception
        !            24:        cmpl    r2,$1           # If divisor <= 1 (signed),
        !            25:        jleq    2f              #  no division is necessary
        !            26: 1:     clrl    r1              # Zero-extend the dividend
        !            27:        ediv    r2,r0,r0,r2     # Divide.  q->r0, r->r2 (discarded)
        !            28:        ret
        !            29: 2:     jeql    4f              # If divisor=1, return dividend
        !            30:        cmpl    r0,r2           # Unsigned comparison between
        !            31:        jgequ   3f              #  dividend and divisor
        !            32:        clrl    r0              # Dividend < divisor, return 0
        !            33:        ret
        !            34: 3:     movl    $1,r0           # Dividend >= divisor, return 1
        !            35: 4:     ret
        !            36: 
        !            37: 

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