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Assembly Source File  |  1986-07-05  |  1KB  |  46 lines
  1. *\ RND.ASM                                             From: AMIGA.3955
  2. *  :ts=8 bk=0
  3. * Yet Another random number generator.  By Leo Schwab.
  4. * Based on an idea posted on the USENET (Thanks, Sam Dicker!)
  5. * For the MetaComCo assembler
  6. *
  7. * Calling convention:
  8. *  long rnd (range);
  9. *  long range;
  10. *
  11. * Assembling:
  12. *  df1:c/assem rnd.asm -o rnd.o
  13. * 
  14. * 8606.30
  15. */
  16.  
  17.                 section code
  18.                 xdef    _rnd
  19.  
  20. _rnd            lea     rndseed,a0      Get address of seed
  21.                 move.l  4(sp),d1        Get range argument
  22.                 tst.l   d1
  23.                 ble.s   setseed         Go reset seed
  24.  
  25.  
  26.                 move.l  (a0),d0         Get seed
  27.                 ADD.L   D0,D0
  28.                 BHI.S   over
  29.                 EORI.L  #$1D872B41,D0
  30. over
  31.                 move.l  d0,(a0)         Save new seed
  32.                 andi.l  #$ffff,d0       Coerce into word
  33.                 andi.l  #$ffff,d1
  34.                 divu    d1,d0           Divide by range
  35.                 swap    d0               and get remainder (modulus)
  36.                 ext.l   d0
  37.                 rts
  38.  
  39. setseed         neg.l   d1              Probably don't need this
  40.                 move.l  d1,(a0)
  41.                 rts
  42.  
  43.                 section data
  44. rndseed         dc.l    0
  45.                 end
  46.