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     mask = GetTrapAlloc(ThisTask);
  49
  50     /* Will any trap do? */
  51     if(trapNum < 0)
  52     {
  53         /*
  54          * To get the last nonzero bit in a number I use a&~a+1:
  55          * Given a number that ends with a row of zeros  xxxx1000
  56          * I first toggle all bits in that number        XXXX0111
  57          * then add 1 to toggle all but the last 0 again XXXX1000
  58          * and AND this with the original number         00001000
  59          *
  60          * And since ~a+1=-a I can use a&-a instead.
  61          *
  62          * And to get the last zero bit I finally use ~a&-~a.
  63          */
  64         mask1 = ~mask & - ~mask;
  65
  66         /* Is the bit already allocated? */
  67         if(mask1 == 0)
  68             return -1;
  69
  70         /* And get the bit number */
  71         trapNum = (mask1 & 0xff00 ? 8 : 0) + (mask1 & 0xf0f0 ? 4 : 0) +
  72                   (mask1 & 0xcccc ? 2 : 0) + (mask1 & 0xaaaa ? 1 : 0);
  73     }
  74     else
  75     {
  76         mask1 = 1 << trapNum;
  77
  78         /* If trap bit is already allocated, return. */
  79         if(mask & mask1)
  80             return -1;
  81     }
  82
  83     if (ThisTask->tc_Flags & TF_ETASK) {
  84         struct ETask *et = ThisTask->tc_UnionETask.tc_ETask;
  85
  86         et->et_TrapAlloc |= mask1;
  87     } else
  88         ThisTask->tc_TrapAlloc |= mask1;
  89
  90     return trapNum;
  91     AROS_LIBFUNC_EXIT
  92 } /* AllocTrap() */