# 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
