Method test_long_asnativebytes

Lib/test/test_capi/test_long.py:355–520

(self)

        self.assertEqual(buffer.count(0), len(buffer) - 1)

    def test_long_asnativebytes(self):
        import math
        from _testcapi import (
            pylong_asnativebytes as asnativebytes,
            SIZE_MAX,
        )

        # Abbreviate sizeof(Py_ssize_t) to SZ because we use it a lot
        SZ = int(math.ceil(math.log(SIZE_MAX + 1) / math.log(2)) / 8)
        MAX_SSIZE = 2 ** (SZ * 8 - 1) - 1
        MAX_USIZE = 2 ** (SZ * 8) - 1
        if support.verbose:
            print(f"SIZEOF_SIZE={SZ}\n{MAX_SSIZE=:016X}\n{MAX_USIZE=:016X}")

        # These tests check that the requested buffer size is correct.
        # This matches our current implementation: We only specify that the
        # return value is a size *sufficient* to hold the result when queried
        # using n_bytes=0. If our implementation changes, feel free to update
        # the expectations here -- or loosen them to be range checks.
        # (i.e. 0 *could* be stored in 1 byte and 512 in 2)
        for v, expect in [
            (0, SZ),
            (512, SZ),
            (-512, SZ),
            (MAX_SSIZE, SZ),
            (MAX_USIZE, SZ + 1),
            (-MAX_SSIZE, SZ),
            (-MAX_USIZE, SZ + 1),
            (2**255-1, 32),
            (-(2**255-1), 32),
            (2**255, 33),
            (-(2**255), 33), # if you ask, we'll say 33, but 32 would do
            (2**256-1, 33),
            (-(2**256-1), 33),
            (2**256, 33),
            (-(2**256), 33),
        ]:
            with self.subTest(f"sizeof-{v:X}"):
                buffer = bytearray(b"\x5a")
                self.assertEqual(expect, asnativebytes(v, buffer, 0, -1),
                    "PyLong_AsNativeBytes(v, <unknown>, 0, -1)")
                self.assertEqual(buffer, b"\x5a",
                    "buffer overwritten when it should not have been")
                # Also check via the __index__ path.
                # We pass Py_ASNATIVEBYTES_NATIVE_ENDIAN | ALLOW_INDEX
                self.assertEqual(expect, asnativebytes(Index(v), buffer, 0, 3 | 16),
                    "PyLong_AsNativeBytes(Index(v), <unknown>, 0, -1)")
                self.assertEqual(buffer, b"\x5a",
                    "buffer overwritten when it should not have been")

        # Test that we populate n=2 bytes but do not overwrite more.
        buffer = bytearray(b"\x99"*3)
        self.assertEqual(2, asnativebytes(4, buffer, 2, 0),  # BE
            "PyLong_AsNativeBytes(v, <3 byte buffer>, 2, 0)  // BE")
        self.assertEqual(buffer, b"\x00\x04\x99")
        self.assertEqual(2, asnativebytes(4, buffer, 2, 1),  # LE
            "PyLong_AsNativeBytes(v, <3 byte buffer>, 2, 1)  // LE")
        self.assertEqual(buffer, b"\x04\x00\x99")