arch/m68k-all/libgcc1/_divmodsi3.s

   1 | 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. We gain some extra speed by inlining
  13 | the division code here instead of calling _udivsi3.
  14
  15         .text
  16         .even
  17         .globl  __divsi3
  18         .globl  __modsi3
  19
  20 __divsi3:
  21         movel   %d2,%a0         | save registers
  22         movel   %d3,%a1
  23         clrw    %sp@-           | sign flag
  24         clrl    %d0             | prepare result
  25         movel   %sp@(10),%d2    | get divisor
  26         beq     L_9             | divisor = 0 causes a division trap
  27         bpl     L_00            | divisor < 0 ?
  28         negl    %d2             | negate it
  29         notw    %sp@            | remember sign
  30 L_00:   movel   %sp@(6),%d1     | get dividend
  31         bpl     L_01            | dividend < 0 ?
  32         negl    %d1             | negate it
  33         notw    %sp@            | remember sign
  34 L_01:
  35 |== case 1) divident < divisor
  36         cmpl    %d2,%d1         | is divident smaller then divisor ?
  37         bcs     L_8             | yes, return immediately
  38 |== case 2) divisor has <= 16 significant bits
  39         tstw    %sp@(10)
  40         bne     L_2             | divisor has only 16 bits
  41         movew   %d1,%d3         | save dividend
  42         clrw    %d1             | divide dvd.h by dvs
  43         swap    %d1
  44         beq     L_02            | (no division necessary if dividend zero)
  45         divu    %d2,%d1
  46 L_02:   movew   %d1,%d0         | save quotient.h
  47         swap    %d0
  48         movew   %d3,%d1         | (%d0.h = remainder of prev divu)
  49         divu    %d2,%d1         | divide dvd.l by dvs
  50         movew   %d1,%d0         | save quotient.l
  51         clrw    %d1             | get remainder
  52         swap    %d1
  53         bra     L_8             | and return
  54 |== case 3) divisor > 16 bits (corollary is dividend > 16 bits, see case 1)
  55 L_2:
  56         moveq   #31,%d3         | loop count
  57 L_3:
  58         addl    %d1,%d1         | shift divident ...
  59         addxl   %d0,%d0         |  ... into %d0
  60         cmpl    %d2,%d0         | compare with divisor
  61         bcs     L_03
  62         subl    %d2,%d0         | big enough, subtract
  63         addw    #1,%d1          | and note bit into result
  64 L_03:
  65         dbra    %d3,L_3
  66         exg     %d0,%d1         | put quotient and remainder in their registers
  67 L_8:
  68         tstw    %sp@(6)         | must the remainder be corrected ?
  69         bpl     L_04
  70         negl    %d1             | yes, apply sign
  71 | the following line would be correct if modulus is defined as in algebra
  72 |       addl    %sp@(6),%d1     | algebraic correction: modulus can only be >= 0
  73 L_04:   tstw    %sp@+           | result should be negative ?
  74         bpl     L_05
  75         negl    %d0             | yes, negate it
  76 L_05:
  77         movel   %a1,%d3
  78         movel   %a0,%d2
  79         rts
  80 L_9:
  81         divu    %d2,%d1         | cause division trap
  82         bra     L_8             | back to user
  83
  84
  85 __modsi3:
  86         movel   %sp@(8),%sp@-   | push divisor
  87         movel   %sp@(8),%sp@-   | push dividend
  88         jbsr    __divsi3
  89         addql   #8,%sp
  90         movel   %d1,%d0         | return the remainder in %d0
  91         rts