rom/exec/alloctrap.c

   1 /*
   2     Copyright © 1995-2015, The AROS Development Team. All rights reserved.
   3     $Id$
   4
   5     Desc: Allocate a trap
   6     Lang: english
   7 */
   8 #include "exec_intern.h"
   9 #include <proto/exec.h>
  10
  11 /*****************************************************************************
  12
  13     NAME */
  14
  15         AROS_LH1(LONG, AllocTrap,
  16
  17 /*  SYNOPSIS */
  18         AROS_LHA(long, trapNum, D0),
  19
  20 /*  LOCATION */
  21         struct ExecBase *, SysBase, 57, Exec)
  22
  23 /*  FUNCTION
  24
  25     INPUTS
  26
  27     RESULT
  28
  29     NOTES
  30
  31     EXAMPLE
  32
  33     BUGS
  34
  35     SEE ALSO
  36
  37     INTERNALS
  38         Very similar to AllocSignal()
  39
  40 *****************************************************************************/
  41 {
  42     AROS_LIBFUNC_INIT
  43
  44     struct Task *ThisTask = GET_THIS_TASK;
  45     UWORD mask;
  46     UWORD mask1;
  47
  48     if (ThisTask)
  49     {
  50         mask = GetTrapAlloc(ThisTask);
  51
  52         /* Will any trap do? */
  53         if(trapNum < 0)
  54         {
  55         /*
  56         * To get the last nonzero bit in a number I use a&~a+1:
  57         * Given a number that ends with a row of zeros  xxxx1000
  58         * I first toggle all bits in that number         XXXX0111
  59         * then add 1 to toggle all but the last 0 again XXXX1000
  60         * and AND this with the original number  00001000
  61         *
  62         * And since ~a+1=-a I can use a&-a instead.
  63         *
  64         * And to get the last zero bit I finally use ~a&-~a.
  65         */
  66         mask1 = ~mask & - ~mask;
  67
  68         /* Is the bit already allocated? */
  69         if(mask1 == 0)
  70             return -1;
  71
  72         /* And get the bit number */
  73         trapNum = (mask1 & 0xff00 ? 8 : 0) + (mask1 & 0xf0f0 ? 4 : 0) +
  74             (mask1 & 0xcccc ? 2 : 0) + (mask1 & 0xaaaa ? 1 : 0);
  75         }
  76         else
  77         {
  78         mask1 = 1 << trapNum;
  79
  80         /* If trap bit is already allocated, return. */
  81         if(mask & mask1)
  82             return -1;
  83         }
  84
  85         if (ThisTask->tc_Flags & TF_ETASK) {
  86             struct ETask *et = ThisTask->tc_UnionETask.tc_ETask;
  87
  88         et->et_TrapAlloc |= mask1;
  89         } else
  90             ThisTask->tc_TrapAlloc |= mask1;
  91     }
  92
  93     return trapNum;
  94     AROS_LIBFUNC_EXIT
  95 } /* AllocTrap() */