# S/390 __udiv_qrnnd #include <linux/linkage.h> # 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 ENTRY(__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