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From fa355239e70411179c70b16ed4ff7113d8008dad Mon Sep 17 00:00:00 2001
From: Elvis Pranskevichus <elvis@edgedb.com>
Date: Wed, 4 Aug 2021 19:25:44 -0700
Subject: [PATCH] Fix test_none_collisions on 32-bit systems (#69)
There are two issues at play here:
1. Python version of `map_hash` unnecessarily performs hash truncation
even if the hash is already 32-bit wide, which potentially converts
it from signed int to unsigned long.
2. The `test_none_collisions` test generates a collision node with
hash greater than 2^32.
Both of these are problematic on 32-bit systems, where `sizeof(Py_hash_t)`
is 4, and so anything that doesn't fit into `Py_hash_t` gets bit-mangled,
breaking the `hash(x) != x` invariance that the test relies upon.
Fixes: #53
Fixes: #50
---
.github/workflows/tests.yml | 10 +++++++++-
immutables/map.py | 5 ++++-
tests/test_none_keys.py | 14 +++++++++-----
3 files changed, 22 insertions(+), 7 deletions(-)
diff --git a/immutables/map.py b/immutables/map.py
index 2c1ffa91..0ad28588 100644
--- a/immutables/map.py
+++ b/immutables/map.py
@@ -19,7 +19,10 @@
def map_hash(o):
x = hash(o)
- return (x & 0xffffffff) ^ ((x >> 32) & 0xffffffff)
+ if sys.hash_info.width > 32:
+ return (x & 0xffffffff) ^ ((x >> 32) & 0xffffffff)
+ else:
+ return x
def map_mask(hash, shift):
diff --git a/tests/test_none_keys.py b/tests/test_none_keys.py
index 8c0bb379..26d4220b 100644
--- a/tests/test_none_keys.py
+++ b/tests/test_none_keys.py
@@ -1,3 +1,4 @@
+import ctypes
import unittest
from immutables.map import map_hash, map_mask, Map as PyMap
@@ -6,16 +7,19 @@
none_hash = map_hash(None)
assert(none_hash != 1)
-assert((none_hash >> 32) == 0)
+assert(none_hash.bit_length() <= 32)
-not_collision = 0xffffffff & (~none_hash)
+none_hash_u = ctypes.c_size_t(none_hash).value
+not_collision = 0xffffffff & (~none_hash_u)
mask = 0x7ffffffff
-none_collisions = [none_hash & (mask >> shift)
+none_collisions = [none_hash_u & (mask >> shift)
for shift in reversed(range(0, 32, 5))]
assert(len(none_collisions) == 7)
-none_collisions = [h | (not_collision & (mask << shift))
- for shift, h in zip(range(5, 37, 5), none_collisions)]
+none_collisions = [
+ ctypes.c_ssize_t(h | (not_collision & (mask << shift))).value
+ for shift, h in zip(range(5, 37, 5), none_collisions)
+]
class NoneCollision(HashKey):
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