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# S/390 __udiv_qrnnd

# r2 : &__r

# r3 : upper half of 64 bit word n

# r4 : lower half of 64 bit word n

# r5 : divisor d

# the reminder r of the division is to be stored to &__r and

# the quotient q is to be returned

        .text

        .globl __udiv_qrnnd

__udiv_qrnnd:

        st    %r2,24(%r15)        # store pointer to reminder for later

        lr    %r0,%r3             # reload n

        lr    %r1,%r4

        ltr   %r2,%r5             # reload and test divisor

        jp    5f

        # divisor >= 0x80000000

        srdl  %r0,2               # n/4

        srl   %r2,1               # d/2

        slr   %r1,%r2             # special case if last bit of d is set

        brc   3,0f                #  (n/4) div (n/2) can overflow by 1

        ahi   %r0,-1              #  trick: subtract n/2, then divide

0:      dr    %r0,%r2             # signed division

        ahi   %r1,1               #  trick part 2: add 1 to the quotient

        # now (n >> 2) = (d >> 1) * %r1 + %r0

        lhi   %r3,1

        nr    %r3,%r1             # test last bit of q

        jz    1f

        alr   %r0,%r2             # add (d>>1) to r

1:      srl   %r1,1               # q >>= 1

        # now (n >> 2) = (d&-2) * %r1 + %r0

        lhi   %r3,1

        nr    %r3,%r5             # test last bit of d

        jz    2f

        slr   %r0,%r1             # r -= q

        brc   3,2f                # borrow ?

        alr   %r0,%r5             # r += d

        ahi   %r1,-1

2:      # now (n >> 2) = d * %r1 + %r0

        alr   %r1,%r1             # q <<= 1

        alr   %r0,%r0             # r <<= 1

        brc   12,3f               # overflow on r ?

        slr   %r0,%r5             # r -= d

        ahi   %r1,1               # q += 1

3:      lhi   %r3,2

        nr    %r3,%r4             # test next to last bit of n

        jz    4f

        ahi   %r0,1               # r += 1

4:      clr   %r0,%r5             # r >= d ?

        jl    6f

        slr   %r0,%r5             # r -= d

        ahi   %r1,1               # q += 1

        # now (n >> 1) = d * %r1 + %r0

        j     6f

5:      # divisor < 0x80000000

        srdl  %r0,1

        dr    %r0,%r2             # signed division

        # now (n >> 1) = d * %r1 + %r0

6:      alr   %r1,%r1             # q <<= 1

        alr   %r0,%r0             # r <<= 1

        brc   12,7f               # overflow on r ?

        slr   %r0,%r5             # r -= d

        ahi   %r1,1               # q += 1

7:      lhi   %r3,1

        nr    %r3,%r4             # isolate last bit of n

        alr   %r0,%r3             # r += (n & 1)

        clr   %r0,%r5             # r >= d ?

        jl    8f

        slr   %r0,%r5             # r -= d

        ahi   %r1,1               # q += 1

8:      # now n = d * %r1 + %r0

        l     %r2,24(%r15)

        st    %r0,0(%r2)

        lr    %r2,%r1

        br    %r14

        .end    __udiv_qrnnd