Get rid of the superstitious "~" in dict hashing's "i = (~hash) & mask".

The comment following used to say:
	/* We use ~hash instead of hash, as degenerate hash functions, such
	   as for ints <sigh>, can have lots of leading zeros. It's not
	   really a performance risk, but better safe than sorry.
	   12-Dec-00 tim:  so ~hash produces lots of leading ones instead --
	   what's the gain? */
That is, there was never a good reason for doing it.  And to the contrary,
as explained on Python-Dev last December, it tended to make the *sum*
(i + incr) & mask (which is the first table index examined in case of
collison) the same "too often" across distinct hashes.

Changing to the simpler "i = hash & mask" reduced the number of string-dict
collisions (== # number of times we go around the lookup for-loop) from about
6 million to 5 million during a full run of the test suite (these are
approximate because the test suite does some random stuff from run to run).
The number of collisions in non-string dicts also decreased, but not as
dramatically.

Note that this may, for a given dict, change the order (wrt previous
releases) of entries exposed by .keys(), .values() and .items().  A number
of std tests suffered bogus failures as a result.  For dicts keyed by
small ints, or (less so) by characters, the order is much more likely to be
in increasing order of key now; e.g.,

>>> d = {}
>>> for i in range(10):
...    d[i] = i
...
>>> d
{0: 0, 1: 1, 2: 2, 3: 3, 4: 4, 5: 5, 6: 6, 7: 7, 8: 8, 9: 9}
>>>

Unfortunately. people may latch on to that in small examples and draw a
bogus conclusion.

test_support.py
    Moved test_extcall's sortdict() into test_support, made it stronger,
    and imported sortdict into other std tests that needed it.
test_unicode.py
    Excluced cp875 from the "roundtrip over range(128)" test, because
    cp875 doesn't have a well-defined inverse for unicode("?", "cp875").
    See Python-Dev for excruciating details.
Cookie.py
    Chaged various output functions to sort dicts before building
    strings from them.
test_extcall
    Fiddled the expected-result file.  This remains sensitive to native
    dict ordering, because, e.g., if there are multiple errors in a
    keyword-arg dict (and test_extcall sets up many cases like that), the
    specific error Python complains about first depends on native dict
    ordering.

1 files changed, 10 insertions, 10 deletions

diff --git a/Lib/test/output/test_extcall b/Lib/test/output/test_extcall
index 58f52d4..24e8c8c 100644
--- a/Lib/test/output/test_extcall
+++ b/Lib/test/output/test_extcall
@@ -40,7 +40,7 @@ za () {} -> za() takes exactly 1 argument (0 given)
 za () {'a': 'aa'} -> ok za aa B D E V a
 za () {'d': 'dd'} -> za() got an unexpected keyword argument 'd'
 za () {'a': 'aa', 'd': 'dd'} -> za() got an unexpected keyword argument 'd'
-za () {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> za() got an unexpected keyword argument 'd'
+za () {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> za() got an unexpected keyword argument 'b'
 za (1, 2) {} -> za() takes exactly 1 argument (2 given)
 za (1, 2) {'a': 'aa'} -> za() takes exactly 1 non-keyword argument (2 given)
 za (1, 2) {'d': 'dd'} -> za() takes exactly 1 non-keyword argument (2 given)
@@ -59,8 +59,8 @@ zade () {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zade() got an unexpected
 zade (1, 2) {} -> ok zade 1 B 2 e V e
 zade (1, 2) {'a': 'aa'} -> zade() got multiple values for keyword argument 'a'
 zade (1, 2) {'d': 'dd'} -> zade() got multiple values for keyword argument 'd'
-zade (1, 2) {'a': 'aa', 'd': 'dd'} -> zade() got multiple values for keyword argument 'd'
-zade (1, 2) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zade() got multiple values for keyword argument 'd'
+zade (1, 2) {'a': 'aa', 'd': 'dd'} -> zade() got multiple values for keyword argument 'a'
+zade (1, 2) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zade() got multiple values for keyword argument 'a'
 zade (1, 2, 3, 4, 5) {} -> zade() takes at most 3 arguments (5 given)
 zade (1, 2, 3, 4, 5) {'a': 'aa'} -> zade() takes at most 3 non-keyword arguments (5 given)
 zade (1, 2, 3, 4, 5) {'d': 'dd'} -> zade() takes at most 3 non-keyword arguments (5 given)
@@ -75,7 +75,7 @@ zabk (1, 2) {} -> ok zabk 1 2 D E V {}
 zabk (1, 2) {'a': 'aa'} -> zabk() got multiple values for keyword argument 'a'
 zabk (1, 2) {'d': 'dd'} -> ok zabk 1 2 D E V {'d': 'dd'}
 zabk (1, 2) {'a': 'aa', 'd': 'dd'} -> zabk() got multiple values for keyword argument 'a'
-zabk (1, 2) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zabk() got multiple values for keyword argument 'b'
+zabk (1, 2) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zabk() got multiple values for keyword argument 'a'
 zabk (1, 2, 3, 4, 5) {} -> zabk() takes exactly 2 arguments (5 given)
 zabk (1, 2, 3, 4, 5) {'a': 'aa'} -> zabk() takes exactly 2 non-keyword arguments (5 given)
 zabk (1, 2, 3, 4, 5) {'d': 'dd'} -> zabk() takes exactly 2 non-keyword arguments (5 given)
@@ -90,12 +90,12 @@ zabdv (1, 2) {} -> ok zabdv 1 2 d E () e
 zabdv (1, 2) {'a': 'aa'} -> zabdv() got multiple values for keyword argument 'a'
 zabdv (1, 2) {'d': 'dd'} -> ok zabdv 1 2 dd E () d
 zabdv (1, 2) {'a': 'aa', 'd': 'dd'} -> zabdv() got multiple values for keyword argument 'a'
-zabdv (1, 2) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zabdv() got an unexpected keyword argument 'e'
+zabdv (1, 2) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zabdv() got multiple values for keyword argument 'a'
 zabdv (1, 2, 3, 4, 5) {} -> ok zabdv 1 2 3 E (4, 5) e
 zabdv (1, 2, 3, 4, 5) {'a': 'aa'} -> zabdv() got multiple values for keyword argument 'a'
 zabdv (1, 2, 3, 4, 5) {'d': 'dd'} -> zabdv() got multiple values for keyword argument 'd'
-zabdv (1, 2, 3, 4, 5) {'a': 'aa', 'd': 'dd'} -> zabdv() got multiple values for keyword argument 'd'
-zabdv (1, 2, 3, 4, 5) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zabdv() got multiple values for keyword argument 'd'
+zabdv (1, 2, 3, 4, 5) {'a': 'aa', 'd': 'dd'} -> zabdv() got multiple values for keyword argument 'a'
+zabdv (1, 2, 3, 4, 5) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zabdv() got multiple values for keyword argument 'a'
 zabdevk () {} -> zabdevk() takes at least 2 arguments (0 given)
 zabdevk () {'a': 'aa'} -> zabdevk() takes at least 2 non-keyword arguments (1 given)
 zabdevk () {'d': 'dd'} -> zabdevk() takes at least 2 non-keyword arguments (0 given)
@@ -105,9 +105,9 @@ zabdevk (1, 2) {} -> ok zabdevk 1 2 d e () {}
 zabdevk (1, 2) {'a': 'aa'} -> zabdevk() got multiple values for keyword argument 'a'
 zabdevk (1, 2) {'d': 'dd'} -> ok zabdevk 1 2 dd e () {}
 zabdevk (1, 2) {'a': 'aa', 'd': 'dd'} -> zabdevk() got multiple values for keyword argument 'a'
-zabdevk (1, 2) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zabdevk() got multiple values for keyword argument 'b'
+zabdevk (1, 2) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zabdevk() got multiple values for keyword argument 'a'
 zabdevk (1, 2, 3, 4, 5) {} -> ok zabdevk 1 2 3 4 (5,) {}
 zabdevk (1, 2, 3, 4, 5) {'a': 'aa'} -> zabdevk() got multiple values for keyword argument 'a'
 zabdevk (1, 2, 3, 4, 5) {'d': 'dd'} -> zabdevk() got multiple values for keyword argument 'd'
-zabdevk (1, 2, 3, 4, 5) {'a': 'aa', 'd': 'dd'} -> zabdevk() got multiple values for keyword argument 'd'
-zabdevk (1, 2, 3, 4, 5) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zabdevk() got multiple values for keyword argument 'd'
+zabdevk (1, 2, 3, 4, 5) {'a': 'aa', 'd': 'dd'} -> zabdevk() got multiple values for keyword argument 'a'
+zabdevk (1, 2, 3, 4, 5) {'a': 'aa', 'b': 'bb', 'd': 'dd', 'e': 'ee'} -> zabdevk() got multiple values for keyword argument 'a'