| # 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 |