src/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  * Authors: Steve Reinhardt
  29  *          Nathan Binkert
  30  */
  31
  32 #ifndef __BASE_BITFIELD_HH__
  33 #define __BASE_BITFIELD_HH__
  34
  35 #include <inttypes.h>
  36
  37 /**
  38  * Generate a 64-bit mask of 'nbits' 1s, right justified.
  39  */
  40 inline uint64_t
  41 mask(int nbits)
  42 {
  43     return (nbits == 64) ? (uint64_t)-1LL : (1ULL << nbits) - 1;
  44 }
  45
  46
  47
  48 /**
  49  * Extract the bitfield from position 'first' to 'last' (inclusive)
  50  * from 'val' and right justify it.  MSB is numbered 63, LSB is 0.
  51  */
  52 template <class T>
  53 inline
  54 T
  55 bits(T val, int first, int last)
  56 {
  57     int nbits = first - last + 1;
  58     return (val >> last) & mask(nbits);
  59 }
  60
  61 /**
  62  * Mask off the given bits in place like bits() but without shifting.
  63  * msb = 63, lsb = 0
  64  */
  65 template <class T>
  66 inline
  67 T
  68 mbits(T val, int first, int last)
  69 {
  70     return val & (mask(first+1) & ~mask(last));
  71 }
  72
  73 inline uint64_t
  74 mask(int first, int last)
  75 {
  76     return mbits((uint64_t)-1LL, first, last);
  77 }
  78
  79 /**
  80  * Sign-extend an N-bit value to 64 bits.
  81  */
  82 template <int N>
  83 inline
  84 int64_t
  85 sext(uint64_t val)
  86 {
  87     int sign_bit = bits(val, N-1, N-1);
  88     return sign_bit ? (val | ~mask(N)) : val;
  89 }
  90
  91 /**
  92  * Return val with bits first to last set to bit_val
  93  */
  94 template <class T, class B>
  95 inline
  96 T
  97 insertBits(T val, int first, int last, B bit_val)
  98 {
  99     T bmask = mask(first - last + 1) << last;
 100     return ((bit_val << last) & bmask) | (val & ~bmask);
 101 }
 102
 103 /**
 104  * A convenience function to replace bits first to last of val with bit_val
 105  * in place.
 106  */
 107 template <class T, class B>
 108 inline
 109 void
 110 replaceBits(T& val, int first, int last, B bit_val)
 111 {
 112     val = insertBits(val, first, last, bit_val);
 113 }
 114
 115 /**
 116  * Returns the bit position of the MSB that is set in the input
 117  */
 118 inline
 119 int
 120 findMsbSet(uint64_t val) {
 121     int msb = 0;
 122     if (!val)
 123         return 0;
 124     if (bits(val, 63,32)) { msb += 32; val >>= 32; }
 125     if (bits(val, 31,16)) { msb += 16; val >>= 16; }
 126     if (bits(val, 15,8))  { msb += 8;  val >>= 8;  }
 127     if (bits(val, 7,4))   { msb += 4;  val >>= 4;  }
 128     if (bits(val, 3,2))   { msb += 2;  val >>= 2;  }
 129     if (bits(val, 1,1))   { msb += 1; }
 130     return msb;
 131 }
 132
 133
 134
 135 #endif // __BASE_BITFIELD_HH__