base/bitfield.hh

   1 /*
   2  * Copyright (c) 2003-2005 The Regents of The University of Michigan
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions are
   7  * met: redistributions of source code must retain the above copyright
   8  * notice, this list of conditions and the following disclaimer;
   9  * redistributions in binary form must reproduce the above copyright
  10  * notice, this list of conditions and the following disclaimer in the
  11  * documentation and/or other materials provided with the distribution;
  12  * neither the name of the copyright holders nor the names of its
  13  * contributors may be used to endorse or promote products derived from
  14  * this software without specific prior written permission.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  17  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  18  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  19  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  20  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  21  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  22  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  23  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  24  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  26  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  27  */
  28
  29 #ifndef __BASE_BITFIELD_HH__
  30 #define __BASE_BITFIELD_HH__
  31
  32 #include "sim/host.hh"
  33
  34 /**
  35  * Generate a 64-bit mask of 'nbits' 1s, right justified.
  36  */
  37 inline uint64_t
  38 mask(int nbits)
  39 {
  40     return (nbits == 64) ? (uint64_t)-1LL : (1ULL << nbits) - 1;
  41 }
  42
  43
  44 /**
  45  * Extract the bitfield from position 'first' to 'last' (inclusive)
  46  * from 'val' and right justify it.  MSB is numbered 63, LSB is 0.
  47  */
  48 template <class T>
  49 inline
  50 T
  51 bits(T val, int first, int last)
  52 {
  53     int nbits = first - last + 1;
  54     return (val >> last) & mask(nbits);
  55 }
  56
  57 /**
  58  * Sign-extend an N-bit value to 64 bits.
  59  */
  60 template <int N>
  61 inline
  62 int64_t
  63 sext(uint64_t val)
  64 {
  65     int sign_bit = bits(val, N-1, N-1);
  66     return sign_bit ? (val | ~mask(N)) : val;
  67 }
  68
  69 #endif // __BASE_BITFIELD_HH__