intmath.hh revision 2 
1/*
2 * Copyright (c) 2003 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 __INTMATH_H__
30#define __INTMATH_H__
31
32// Returns the prime number one less than n.
33int PrevPrime(int n);
34
35// Determine if a number is prime
36inline bool
37IsPrime(int n)
38{
39  int i;
40
41  if (n == 2 || n == 3)
42    return true;
43
44  // Don't try every odd number to prove if it is a prime.
45  // Toggle between every 2nd and 4th number.
46  // (This is because every 6th odd number is divisible by 3.)
47  for (i = 5; i*i <= n; i += 6) {
48    if (((n % i) == 0 ) || ((n % (i + 2)) == 0) ) {
49      return false;
50    }
51  }
52
53  return true;
54}
55
56inline unsigned
57LeastSigBit(unsigned n)
58{ return n & ~(n - 1); }
59
60inline bool
61IsPowerOf2(unsigned n)
62{ return n != 0 && LeastSigBit(n) == n; }
63
64inline int
65FloorLog2(unsigned x)
66{
67  if (x == 0)
68    return -1;
69
70  int y = 0;
71
72  if (x & 0xffff0000) { y += 16; x >>= 16; }
73  if (x & 0x0000ff00) { y +=  8; x >>=  8; }
74  if (x & 0x000000f0) { y +=  4; x >>=  4; }
75  if (x & 0x0000000c) { y +=  2; x >>=  2; }
76  if (x & 0x00000002) { y +=  1; }
77
78  return y;
79}
80
81inline int
82CeilLog2(unsigned n)
83{ return FloorLog2(n-1)+1; }
84
85inline unsigned
86FloorPow2(unsigned n)
87{ return 1 << FloorLog2(n); }
88
89inline unsigned
90CeilPow2(unsigned n)
91{ return 1 << CeilLog2(n); }
92
93inline bool
94IsHex(char c)
95{ return (c >= '0' && c <= '9' ||
96          c >= 'A' && c <= 'F' ||
97          c >= 'a' && c <= 'f');
98}
99
100inline bool
101IsOct(char c)
102{ return (c >= '0' && c <= '7'); }
103
104inline bool
105IsDec(char c)
106{ return (c >= '0' && c <= '9'); }
107
108inline int
109Hex2Int(char c)
110{
111  if (c >= '0' && c <= '9')
112    return (c - '0');
113
114  if(c >= 'A' && c <= 'F')
115    return (c - 'A') + 10;
116
117  if (c >= 'a' && c <= 'f')
118    return (c - 'a') + 10;
119
120  return 0;
121}
122
123#endif // __INTMATH_H__
124