1 #!/usr/bin/env python 2 3 """ 4 Variable-length integer functions. 5 6 Copyright (C) 2009 Paul Boddie <paul@boddie.org.uk> 7 8 This program is free software; you can redistribute it and/or modify it under 9 the terms of the GNU General Public License as published by the Free Software 10 Foundation; either version 3 of the License, or (at your option) any later 11 version. 12 13 This program is distributed in the hope that it will be useful, but WITHOUT ANY 14 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A 15 PARTICULAR PURPOSE. See the GNU General Public License for more details. 16 17 You should have received a copy of the GNU General Public License along 18 with this program. If not, see <http://www.gnu.org/licenses/>. 19 """ 20 21 from array import array 22 23 vint_cache = {} 24 25 def vint(number): 26 27 "Write 'number' as a variable-length integer." 28 29 try: 30 return vint_cache[number] 31 except KeyError: 32 if number >= 0: 33 34 # Write the number from least to most significant digits. 35 36 bytes = array('B') 37 38 while number > 127: 39 bytes.append(number & 127 | 128) 40 number = number >> 7 41 else: 42 bytes.append(number) 43 44 return bytes.tostring() 45 46 # Negative numbers are not supported. 47 48 else: 49 raise ValueError, "Number %r is negative." % number 50 51 for i in xrange(0, 65536): 52 vint_cache[i] = vint(i) 53 54 # vim: tabstop=4 expandtab shiftwidth=4