qrnnd.S
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上传日期：2013-02-24
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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
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