[pypy-commit] pypy default: (fijal, arigo) improve the random generation a bit

[fijal]

Author: Maciej Fijalkowski <fijall at gmail.com>
Branch: 
Changeset: r74154:ae4c7b57097a
Date: 2014-10-24 11:15 +0200
http://bitbucket.org/pypy/pypy/changeset/ae4c7b57097a/

Log:	(fijal, arigo) improve the random generation a bit

diff --git a/rpython/rlib/rrandom.py b/rpython/rlib/rrandom.py
--- a/rpython/rlib/rrandom.py
+++ b/rpython/rlib/rrandom.py
@@ -4,7 +4,7 @@
 
 # this is stolen from CPython's _randommodule.c
 
-from rpython.rlib.rarithmetic import r_uint
+from rpython.rlib.rarithmetic import r_uint, intmask
 
 N = 624
 M = 397
@@ -72,18 +72,23 @@
                 i = 1
         mt[0] = UPPER_MASK
 
+    def _conditionally_apply(self, val, y):
+        if y & r_uint(1):
+            return val ^ MATRIX_A
+        return val
+
     def genrand32(self):
-        mag01 = [0, MATRIX_A]
         mt = self.state
         if self.index >= N:
             for kk in range(N - M):
                 y = (mt[kk] & UPPER_MASK) | (mt[kk + 1] & LOWER_MASK)
-                mt[kk] = mt[kk+M] ^ (y >> 1) ^ mag01[y & r_uint(1)]
+                mt[kk] = self._conditionally_apply(mt[kk+M] ^ (y >> 1), y)
             for kk in range(N - M, N - 1):
                 y = (mt[kk] & UPPER_MASK) | (mt[kk + 1] & LOWER_MASK)
-                mt[kk] = mt[kk + (M - N)] ^ (y >> 1) ^ mag01[y & r_uint(1)]
+                mt[kk] = self._conditionally_apply(mt[kk + (M - N)] ^ (y >> 1),
+                                                   y)
             y = (mt[N - 1] & UPPER_MASK) | (mt[0] & LOWER_MASK)
-            mt[N - 1] = mt[M - 1] ^ (y >> 1) ^ mag01[y & r_uint(1)]
+            mt[N - 1] = self._conditionally_apply(mt[M - 1] ^ (y >> 1), y)
             self.index = 0
         y = mt[self.index]
         self.index += 1
@@ -94,8 +99,8 @@
         return y
 
     def random(self):
-        a = self.genrand32() >> 5
-        b = self.genrand32() >> 6
+        a = intmask(self.genrand32() >> 5)
+        b = intmask(self.genrand32() >> 6)
         return (a * 67108864.0 + b) * (1.0 / 9007199254740992.0)
 
     def jumpahead(self, n):