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src/msgspec/_core.c: Fix backing type declaration of Ext.code - #1135

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msgspec:mainfrom
OPNA2608:fix/Ext.code-big-endian
Aug 11, 2026
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src/msgspec/_core.c: Fix backing type declaration of Ext.code#1135
sobolevn merged 2 commits into
msgspec:mainfrom
OPNA2608:fix/Ext.code-big-endian

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@OPNA2608 OPNA2608 commented Aug 7, 2026

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Fixes the TestExt test suite on big-endian systems.

(Ext).code is implemented by a long in the C code, but declared to be backed by an int for access from Python. Correct this.

When long is larger than int, the previous declaration caused only an endian-specific part of the code value to get returned when read from Python-land. On little-endian it was the lower half, and with the valid range of code values being small enough to fit in 1 byte, everything seemed fine.

On big-endian, this returned the upper half of the long instead, so all asserts of (Ext).code values failed because the only possible values were 0 and -1.

Example output of the tests on a big-endian machine (powerpc64-linux) before this change:

=========================== short test summary info ============================
FAILED tests/unit/test_msgpack.py::TestExt::test_init[test] - assert 0 == 1
FAILED tests/unit/test_msgpack.py::TestExt::test_init[data1] - assert 0 == 1
FAILED tests/unit/test_msgpack.py::TestExt::test_init[data2] - assert 0 == 1
FAILED tests/unit/test_msgpack.py::TestExt::test_code_roundtrip[-128] - assert -1 == -128
FAILED tests/unit/test_msgpack.py::TestExt::test_code_roundtrip[-2] - assert -1 == -2
FAILED tests/unit/test_msgpack.py::TestExt::test_code_roundtrip[2] - assert 0 == 2
FAILED tests/unit/test_msgpack.py::TestExt::test_code_roundtrip[127] - assert 0 == 127
FAILED tests/unit/test_msgpack.py::TestExt::test_pickleable - assert 0 == 1
FAILED tests/unit/test_msgpack.py::TestExt::test_roundtrip[0] - assert 0 == 5
FAILED tests/unit/test_msgpack.py::TestExt::test_roundtrip[1] - assert 0 == 5
FAILED tests/unit/test_msgpack.py::TestExt::test_roundtrip[2] - assert 0 == 5
FAILED tests/unit/test_msgpack.py::TestExt::test_roundtrip[4] - assert 0 == 5
FAILED tests/unit/test_msgpack.py::TestExt::test_roundtrip[8] - assert 0 == 5
FAILED tests/unit/test_msgpack.py::TestExt::test_roundtrip[16] - assert 0 == 5
FAILED tests/unit/test_msgpack.py::TestExt::test_roundtrip[31] - assert 0 == 5
FAILED tests/unit/test_msgpack.py::TestExt::test_roundtrip[32] - assert 0 == 5
FAILED tests/unit/test_msgpack.py::TestExt::test_roundtrip[255] - assert 0 == 5
FAILED tests/unit/test_msgpack.py::TestExt::test_roundtrip[256] - assert 0 == 5
FAILED tests/unit/test_msgpack.py::TestExt::test_roundtrip[65535] - assert 0 == 5
FAILED tests/unit/test_msgpack.py::TestExt::test_roundtrip[65536] - assert 0 == 5
=========== 20 failed, 5798 passed, 379 skipped in 74.33s (0:01:14) ============

@OPNA2608
src/msgspec/_core.c: Fix backing type declaration of Ext.code
85a1278 
Fixes the TestExt test suite on big-endian systems.

`(Ext).code` is implemented by a `long` in the C code, but declared to be backed by an `int` for access from Python. Correct this.

When `long` is larger than `int`, the previous declaration caused only an endian-specific part of the `code` value to get
returned when read from Python-land. On little-endian it was the lower half, and with the valid range of `code` values being
small enough to fit in 1 byte, everything seemed fine.

On big-endian, this returned the upper half of the `long` instead, so all `assert`s of `(Ext).code` values failed because
the only possible values were 0 and -1.
jcrist
jcrist approved these changes Aug 7, 2026
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Thanks!

@OPNA2608 OPNA2608 mentioned this pull request Aug 7, 2026
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@codspeed-hq

codspeed-hq Bot commented Aug 7, 2026 •
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Merging this PR will improve performance by ×12

⚡ 2 improved benchmarks
✅ 137 untouched benchmarks
⏩ 135 skipped benchmarks1

Performance Changes

Mode Benchmark BASE HEAD Efficiency
⚡ Simulation test_import_time[arm-msgspec.inspect] 17,133.4 µs 137.5 µs ×120
⚡ Simulation test_decode_type[arm-msgpack-False] 849.5 µs 758.6 µs +11.98%

Tip

Curious why this is faster? Comment @codspeedbot explain why this is faster on this PR, or directly use the CodSpeed MCP with your agent.

Comparing OPNA2608:fix/Ext.code-big-endian (dc8bca6) with main (dcfd447)

Open in CodSpeed

Footnotes

  1. 135 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

sobolevn
sobolevn approved these changes Aug 11, 2026
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Thank you!
It will make into the 0.22.0 release.

@sobolevn
sobolevn added this pull request to the merge queue Aug 11, 2026
Merged via the queue into msgspec:main with commit c24bc70 Aug 11, 2026
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