libutils/primes.py

#!/usr/bin/env python2.6
#
# Copyright (C) 2011 The Android Open Source Project
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#

#
# Generates a table of prime numbers for use in BasicHashtable.cpp.
#
# Each prime is chosen such that it is a little more than twice as large as
# the previous prime in the table.  This makes it easier to choose a new
# hashtable size when the underlying array is grown by as nominal factor
# of two each time.
#

def is_odd_prime(n):
  limit = (n - 1) / 2
  d = 3
  while d <= limit:
    if n % d == 0:
      return False
    d += 2
  return True

print "static size_t PRIMES[] = {"

n = 5
max = 2**31 - 1
while n < max:
  print "    %d," % (n)
  n = n * 2 + 1
  while not is_odd_prime(n):
    n += 2

print "    0,"
print "};"