rom/exec/alloctrap.c

   1 /*
   2     Copyright © 1995-2007, 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;
  45     UWORD mask;
  46     UWORD mask1;
  47
  48     ThisTask = FindTask(NULL);
  49     mask = GetTrapAlloc(ThisTask);
  50
  51     /* Will any trap do? */
  52     if(trapNum < 0)
  53     {
  54         /*
  55          * To get the last nonzero bit in a number I use a&~a+1:
  56          * Given a number that ends with a row of zeros  xxxx1000
  57          * I first toggle all bits in that number        XXXX0111
  58          * then add 1 to toggle all but the last 0 again XXXX1000
  59          * and AND this with the original number         00001000
  60          *
  61          * And since ~a+1=-a I can use a&-a instead.
  62          *
  63          * And to get the last zero bit I finally use ~a&-~a.
  64          */
  65         mask1 = ~mask & - ~mask;
  66
  67         /* Is the bit already allocated? */
  68         if(mask1 == 0)
  69             return -1;
  70
  71         /* And get the bit number */
  72         trapNum = (mask1 & 0xff00 ? 8 : 0) + (mask1 & 0xf0f0 ? 4 : 0) +
  73                   (mask1 & 0xcccc ? 2 : 0) + (mask1 & 0xaaaa ? 1 : 0);
  74     }
  75     else
  76     {
  77         mask1 = 1 << trapNum;
  78
  79         /* If trap bit is already allocated, return. */
  80         if(mask & mask1)
  81             return -1;
  82     }
  83
  84     if (ThisTask->tc_Flags & TF_ETASK) {
  85         struct ETask *et = ThisTask->tc_UnionETask.tc_ETask;
  86
  87         et->et_TrapAlloc |= mask1;
  88     } else
  89         ThisTask->tc_TrapAlloc |= mask1;
  90
  91     return trapNum;
  92     AROS_LIBFUNC_EXIT
  93 } /* AllocTrap() */