Index: random.py
===================================================================
RCS file: /cvsroot/python/python/dist/src/Lib/random.py,v
retrieving revision 1.51.8.3
diff -c -r1.51.8.3 random.py
*** random.py	8 Sep 2003 19:15:43 -0000	1.51.8.3
--- random.py	29 Sep 2003 15:49:51 -0000
***************
*** 53,58 ****
--- 53,59 ----
  TWOPI = 2.0*_pi
  LOG4 = _log(4.0)
  SG_MAGICCONST = 1.0 + _log(4.5)
+ BPR = 53        # Number of bits in a float
  
  # Translated by Guido van Rossum from C source provided by
  # Adrian Baddeley.  Adapted by Raymond Hettinger for use with
***************
*** 131,142 ****
  
  ## -------------------- integer methods  -------------------
  
!     def randrange(self, start, stop=None, step=1, int=int, default=None):
          """Choose a random item from range(start, stop[, step]).
  
          This fixes the problem with randint() which includes the
          endpoint; in Python this is usually not what you want.
!         Do not supply the 'int' and 'default' arguments.
          """
  
          # This code is a bit messy to make it fast for the
--- 132,144 ----
  
  ## -------------------- integer methods  -------------------
  
!     def randrange(self, start, stop=None, step=1, int=int, default=None,
!                   maxwidth=1L<<BPR):
          """Choose a random item from range(start, stop[, step]).
  
          This fixes the problem with randint() which includes the
          endpoint; in Python this is usually not what you want.
!         Do not supply the 'int', 'default', and 'maxwidth' arguments.
          """
  
          # This code is a bit messy to make it fast for the
***************
*** 146,151 ****
--- 148,155 ----
              raise ValueError, "non-integer arg 1 for randrange()"
          if stop is default:
              if istart > 0:
+                 if istart >= maxwidth:
+                     return self._bigrand(istart)
                  return int(self.random() * istart)
              raise ValueError, "empty range for randrange()"
  
***************
*** 153,159 ****
          istop = int(stop)
          if istop != stop:
              raise ValueError, "non-integer stop for randrange()"
!         if step == 1 and istart < istop:
              # Note that
              #     int(istart + self.random()*(istop - istart))
              # instead would be incorrect.  For example, consider istart
--- 157,164 ----
          istop = int(stop)
          if istop != stop:
              raise ValueError, "non-integer stop for randrange()"
!         width = istop - istart
!         if step == 1 and width > 0:
              # Note that
              #     int(istart + self.random()*(istop - istart))
              # instead would be incorrect.  For example, consider istart
***************
*** 166,172 ****
              # can return a long, and then randrange() would also return
              # a long, but we're supposed to return an int (for backward
              # compatibility).
!             return int(istart + int(self.random()*(istop - istart)))
          if step == 1:
              raise ValueError, "empty range for randrange()"
  
--- 171,179 ----
              # can return a long, and then randrange() would also return
              # a long, but we're supposed to return an int (for backward
              # compatibility).
!             if width >= maxwidth:
!                 return istart + self._bigrand(width)
!             return int(istart + int(self.random()*width))
          if step == 1:
              raise ValueError, "empty range for randrange()"
  
***************
*** 175,188 ****
          if istep != step:
              raise ValueError, "non-integer step for randrange()"
          if istep > 0:
!             n = (istop - istart + istep - 1) / istep
          elif istep < 0:
!             n = (istop - istart + istep + 1) / istep
          else:
              raise ValueError, "zero step for randrange()"
  
          if n <= 0:
              raise ValueError, "empty range for randrange()"
          return istart + istep*int(self.random() * n)
  
      def randint(self, a, b):
--- 182,198 ----
          if istep != step:
              raise ValueError, "non-integer step for randrange()"
          if istep > 0:
!             n = (width + istep - 1) / istep
          elif istep < 0:
!             n = (width + istep + 1) / istep
          else:
              raise ValueError, "zero step for randrange()"
  
          if n <= 0:
              raise ValueError, "empty range for randrange()"
+ 
+         if n >= maxwidth:
+                 return istart + self._bigrand(n)
          return istart + istep*int(self.random() * n)
  
      def randint(self, a, b):
***************
*** 190,195 ****
--- 200,231 ----
          """
  
          return self.randrange(a, b+1)
+ 
+     def _bigrand(self, n, int=int, bpr=BPR, maxwidth=1L<<BPR):
+         """Return a random int in the range [0,n)
+ 
+         Handles the case where n has more bits than returned
+         by a single call to the underlying generator.
+         """
+ 
+         assert n > 0 and n == int(n)
+         random = self.random
+         cumrnd = 0L
+         cumrng = 1L
+         while cumrng <= n:
+             cumrng <<= bpr
+             cumrnd <<= bpr
+             cumrnd |= long(random() * maxwidth)
+ 
+         # Avoid bias by limiting the range to an exact multiple of n.
+         # This assures each [0,n) corresponds to an equal number of
+         # possibilities in the range:  0 <= cumrnd < limit.
+         scale, rem = divmod(cumrng, n)
+         limit = cumrng - rem
+         if cumrnd >= limit:
+             return self._bigrand(n)
+         assert 0 <= cumrnd < n*scale == limit <= limit+rem == cumrng
+         return cumrnd // scale
  
  ## -------------------- sequence methods  -------------------
  
Index: test/test_random.py
===================================================================
RCS file: /cvsroot/python/python/dist/src/Lib/test/test_random.py,v
retrieving revision 1.12.8.2
diff -c -r1.12.8.2 test_random.py
*** test/test_random.py	5 Sep 2003 21:40:30 -0000	1.12.8.2
--- test/test_random.py	29 Sep 2003 15:49:51 -0000
***************
*** 220,225 ****
--- 220,242 ----
          seed = (1L << (10000 * 8)) - 1  # about 10K bytes
          self.gen.seed(seed)
  
+     def test_53_bits_per_float(self):
+         # This should pass whenever a C double has 53 bit precision.
+         span = 2 ** 53
+         cum = 0
+         for i in xrange(50):
+             cum |= int(self.gen.random() * span)
+         self.assertEqual(cum, span-1)
+ 
+     def test_bigrand(self):
+         # The randrange routine should build-up the required number of bits
+         # in stages so that all bit positions are active.
+         span = 2 ** 500
+         cum = 0
+         for i in xrange(50):
+             cum |= self.gen.randrange(span)
+         self.assertEqual(cum, span-1)
+ 
  _gammacoeff = (0.9999999999995183, 676.5203681218835, -1259.139216722289,
                771.3234287757674,  -176.6150291498386, 12.50734324009056,
                -0.1385710331296526, 0.9934937113930748e-05, 0.1659470187408462e-06)