arch/m68k-all/libgcc1/_udivmodsi3.s

   1 | unsigned long division and modulus routines
   2 |
   3 | written by Kai-Uwe Bloem (I5110401@dbstu1.bitnet).
   4 |
   5 |
   6 | Revision 1.1, kub 03-90
   7 | first version, replaces the appropriate routine from fixnum.s.
   8 | Should be faster in more common cases. Division is done by 68000 divu
   9 | operations if divisor is only 16 bits wide. Otherwise the normal division
  10 | algorithm as described in various papers takes place. The division routine
  11 | delivers the quotient in %d0 and the remainder in %d1, thus the implementation
  12 | of the modulo operation is trivial.
  13
  14         .text
  15         .even
  16         .globl  __udivsi3
  17         .globl  __umodsi3
  18
  19 __udivsi3:
  20         movel   %d2,%a0         | save registers
  21         movel   %d3,%a1
  22         clrl    %d0             | prepare result
  23         movel   %sp@(8),%d2     | get divisor
  24         beq     L_9             | divisor = 0 causes a division trap
  25         movel   %sp@(4),%d1     | get dividend
  26 |== case 1) divident < divisor
  27         cmpl    %d2,%d1         | is divident smaller then divisor ?
  28         bcs     L_8             | yes, return immediately
  29 |== case 2) divisor has <= 16 significant bits
  30         tstw    %sp@(8)
  31         bne     L_2             | divisor has only 16 bits
  32         movew   %d1,%d3         | save dividend
  33         clrw    %d1             | divide dvd.h by dvs
  34         swap    %d1
  35         beq     L_00            | (no division necessary if dividend zero)
  36         divu    %d2,%d1
  37 L_00:   movew   %d1,%d0         | save quotient.h
  38         swap    %d0
  39         movew   %d3,%d1         | (%d1.h = remainder of prev divu)
  40         divu    %d2,%d1         | divide dvd.l by dvs
  41         movew   %d1,%d0         | save quotient.l
  42         clrw    %d1             | get remainder
  43         swap    %d1
  44         bra     L_8             | and return
  45 |== case 3) divisor > 16 bits (corollary is dividend > 16 bits, see case 1)
  46 L_2:
  47         moveq   #31,%d3         | loop count
  48 L_3:
  49         addl    %d1,%d1         | shift divident ...
  50         addxl   %d0,%d0         |  ... into %d0
  51         cmpl    %d2,%d0         | compare with divisor
  52         bcs     L_01
  53         subl    %d2,%d0         | big enough, subtract
  54         addw    #1,%d1          | and note bit in result
  55 L_01:
  56         dbra    %d3,L_3
  57         exg     %d0,%d1         | put quotient and remainder in their registers
  58 L_8:
  59         movel   %a1,%d3
  60         movel   %a0,%d2
  61         rts
  62 L_9:
  63         divu    %d2,%d1         | cause division trap
  64         bra     L_8             | back to user
  65
  66
  67 __umodsi3:
  68         movel   %sp@(8),%sp@-   | push divisor
  69         movel   %sp@(8),%sp@-   | push dividend
  70         jbsr    __udivsi3
  71         addql   #8,%sp
  72         movel   %d1,%d0         | return the remainder in %d0
  73         rts