cpython/Lib/test/test_capi/test_hash.py

import sys
import unittest
from test.support import import_helper
_testcapi = import_helper.import_module('_testcapi')


SIZEOF_VOID_P = _testcapi.SIZEOF_VOID_P
SIZEOF_PY_HASH_T = SIZEOF_VOID_P


class CAPITest(unittest.TestCase):
    def test_hash_getfuncdef(self):
        # Test PyHash_GetFuncDef()
        hash_getfuncdef = _testcapi.hash_getfuncdef
        func_def = hash_getfuncdef()

        match func_def.name:
            case "fnv":
                self.assertEqual(func_def.hash_bits, 8 * SIZEOF_PY_HASH_T)
                self.assertEqual(func_def.seed_bits, 16 * SIZEOF_PY_HASH_T)
            case "siphash13":
                self.assertEqual(func_def.hash_bits, 64)
                self.assertEqual(func_def.seed_bits, 128)
            case "siphash24":
                self.assertEqual(func_def.hash_bits, 64)
                self.assertEqual(func_def.seed_bits, 128)
            case _:
                self.fail(f"unknown function name: {func_def.name!r}")

        # compare with sys.hash_info
        hash_info = sys.hash_info
        self.assertEqual(func_def.name, hash_info.algorithm)
        self.assertEqual(func_def.hash_bits, hash_info.hash_bits)
        self.assertEqual(func_def.seed_bits, hash_info.seed_bits)

    def test_hash_pointer(self):
        # Test Py_HashPointer()
        hash_pointer = _testcapi.hash_pointer

        UHASH_T_MASK = ((2 ** (8 * SIZEOF_PY_HASH_T)) - 1)
        HASH_T_MAX = (2 ** (8 * SIZEOF_PY_HASH_T - 1) - 1)

        def python_hash_pointer(x):
            # Py_HashPointer() rotates the pointer bits by 4 bits to the right
            x = (x >> 4) | ((x & 15) << (8 * SIZEOF_VOID_P - 4))

            # Convert unsigned uintptr_t (Py_uhash_t) to signed Py_hash_t
            if HASH_T_MAX < x:
                x = (~x) + 1
                x &= UHASH_T_MASK
                x = (~x) + 1
            return x

        if SIZEOF_VOID_P == 8:
            values = (
                0xABCDEF1234567890,
                0x1234567890ABCDEF,
                0xFEE4ABEDD1CECA5E,
            )
        else:
            values = (
                0x12345678,
                0x1234ABCD,
                0xDEADCAFE,
            )

        for value in values:
            expected = python_hash_pointer(value)
            with self.subTest(value=value):
                self.assertEqual(hash_pointer(value), expected,
                                 f"hash_pointer({value:x}) = "
                                 f"{hash_pointer(value):x} != {expected:x}")

        # Py_HashPointer(NULL) returns 0
        self.assertEqual(hash_pointer(0), 0)

        # Py_HashPointer((void*)(uintptr_t)-1) doesn't return -1 but -2
        VOID_P_MAX = -1 & (2 ** (8 * SIZEOF_VOID_P) - 1)
        self.assertEqual(hash_pointer(VOID_P_MAX), -2)


if __name__ == "__main__":
    unittest.main()