arch/s390/math-emu/qrnnd.S

   1 # S/390 __udiv_qrnnd
   2
   3 # r2 : &__r
   4 # r3 : upper half of 64 bit word n
   5 # r4 : lower half of 64 bit word n
   6 # r5 : divisor d
   7 # the reminder r of the division is to be stored to &__r and
   8 # the quotient q is to be returned
   9
  10         .text
  11         .globl __udiv_qrnnd
  12 __udiv_qrnnd:
  13         st    %r2,24(%r15)        # store pointer to reminder for later
  14         lr    %r0,%r3             # reload n
  15         lr    %r1,%r4
  16         ltr   %r2,%r5             # reload and test divisor
  17         jp    5f
  18         # divisor >= 0x80000000
  19         srdl  %r0,2               # n/4
  20         srl   %r2,1               # d/2
  21         slr   %r1,%r2             # special case if last bit of d is set
  22         brc   3,0f                #  (n/4) div (n/2) can overflow by 1
  23         ahi   %r0,-1              #  trick: subtract n/2, then divide
  24 0:      dr    %r0,%r2             # signed division
  25         ahi   %r1,1               #  trick part 2: add 1 to the quotient
  26         # now (n >> 2) = (d >> 1) * %r1 + %r0
  27         lhi   %r3,1
  28         nr    %r3,%r1             # test last bit of q
  29         jz    1f
  30         alr   %r0,%r2             # add (d>>1) to r
  31 1:      srl   %r1,1               # q >>= 1
  32         # now (n >> 2) = (d&-2) * %r1 + %r0
  33         lhi   %r3,1
  34         nr    %r3,%r5             # test last bit of d
  35         jz    2f
  36         slr   %r0,%r1             # r -= q
  37         brc   3,2f                # borrow ?
  38         alr   %r0,%r5             # r += d
  39         ahi   %r1,-1
  40 2:      # now (n >> 2) = d * %r1 + %r0
  41         alr   %r1,%r1             # q <<= 1
  42         alr   %r0,%r0             # r <<= 1
  43         brc   12,3f               # overflow on r ?
  44         slr   %r0,%r5             # r -= d
  45         ahi   %r1,1               # q += 1
  46 3:      lhi   %r3,2
  47         nr    %r3,%r4             # test next to last bit of n
  48         jz    4f
  49         ahi   %r0,1               # r += 1
  50 4:      clr   %r0,%r5             # r >= d ?
  51         jl    6f
  52         slr   %r0,%r5             # r -= d
  53         ahi   %r1,1               # q += 1
  54         # now (n >> 1) = d * %r1 + %r0
  55         j     6f
  56 5:      # divisor < 0x80000000
  57         srdl  %r0,1
  58         dr    %r0,%r2             # signed division
  59         # now (n >> 1) = d * %r1 + %r0
  60 6:      alr   %r1,%r1             # q <<= 1
  61         alr   %r0,%r0             # r <<= 1
  62         brc   12,7f               # overflow on r ?
  63         slr   %r0,%r5             # r -= d
  64         ahi   %r1,1               # q += 1
  65 7:      lhi   %r3,1
  66         nr    %r3,%r4             # isolate last bit of n
  67         alr   %r0,%r3             # r += (n & 1)
  68         clr   %r0,%r5             # r >= d ?
  69         jl    8f
  70         slr   %r0,%r5             # r -= d
  71         ahi   %r1,1               # q += 1
  72 8:      # now n = d * %r1 + %r0
  73         l     %r2,24(%r15)
  74         st    %r0,0(%r2)
  75         lr    %r2,%r1
  76         br    %r14
  77         .end    __udiv_qrnnd