From fa355239e70411179c70b16ed4ff7113d8008dad Mon Sep 17 00:00:00 2001 From: Elvis Pranskevichus 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):