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Annotation of 41BSD/sys/conf/urem.s, revision 1.1.1.1

1.1       root        1: #
                      2: #      urem - unsigned remainder for vax-11
                      3: #
                      4: #      arguments: dividend, divisor
                      5: #      result: remainder
                      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 0.  If the divisor is 0, do the ediv also,
                     12: #      so it will generate the proper exception.  All other values
                     13: #      of the divisor have bit 31 on: in this case the remainder
                     14: #      must be the dividend if divisor > dividend, and the dividend
                     15: #      minus the divisor otherwise.  The comparison must be unsigned.
                     16: #
                     17:        .text
                     18:        .align  1
                     19:        .globl  urem
                     20: urem:  .word   0x0000
                     21:        movl    4(ap),r0        # Dividend
                     22:        movl    8(ap),r2        # Divisor
                     23:        jeql    div             # If divisor=0, force exception
                     24:        cmpl    r2,$1           # If divisor <= 1 (signed),
                     25:        jleq    nodiv           #  no division is necessary
                     26: div:   clrl    r1              # Zero-extend the dividend
                     27:        ediv    r2,r0,r2,r0     # Divide.  q->r2 (discarded), r->r0
                     28:        ret
                     29: nodiv: jneq    nzero           # If divisor=1, return 0
                     30:        clrl    r0              #  (because doing the divide will overflow
                     31:        ret                     #  if the dividend has its high bit on)
                     32: nzero: cmpl    r0,r2           # If dividend < divisor (unsigned)
                     33:        jlssu   retn            #  remainder is dividend
                     34:        subl2   r2,r0           #  else remainder is dividend - divisor
                     35: retn:  ret
                     36: 
                     37: 

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