pythongh-91349: Expose the crc32 function from the lzma library.

It is faster than the crc32 function from the zlib library.
Update zipfile to detect and use lzma.crc32
zlic.crc32 binascii.crc32, in order of preference.

Author: rmmancom

Doc/library/lzma.rst

@@ -311,6 +311,25 @@ Compressing and decompressing data in memory
    *preset* and *filters* arguments.
 
 
+.. function:: crc32(data[, value])
+
+   .. index::
+      single: Cyclic Redundancy Check
+      single: checksum; Cyclic Redundancy Check
+
+   Computes a CRC (Cyclic Redundancy Check) checksum of *data*. The
+   result is an unsigned 32-bit integer. If *value* is present, it is used
+   as the starting value of the checksum; otherwise, a default value of 0
+   is used.  Passing in *value* allows computing a running checksum over the
+   concatenation of several inputs.  The algorithm is not cryptographically
+   strong, and should not be used for authentication or digital signatures.  Since
+   the algorithm is designed for use as a checksum algorithm, it is not suitable
+   for use as a general hash algorithm.
+
+   .. versionadded:: 3.14
+      The result is always unsigned.
+
+
 .. function:: decompress(data, format=FORMAT_AUTO, memlimit=None, filters=None)
 
    Decompress *data* (a :class:`bytes` object), returning the uncompressed data

Lib/test/test_lzma.py

@@ -1,5 +1,6 @@
 import _compression
 import array
+import binascii
 from io import BytesIO, UnsupportedOperation, DEFAULT_BUFFER_SIZE
 import os
 import pickle
@@ -17,6 +18,45 @@
 lzma = import_module("lzma")
 from lzma import LZMACompressor, LZMADecompressor, LZMAError, LZMAFile
 
+class ChecksumTestCase(unittest.TestCase):
+    # checksum test cases
+    def test_crc32start(self):
+        self.assertEqual(lzma.crc32(b""), lzma.crc32(b"", 0))
+        self.assertTrue(lzma.crc32(b"abc", 0xffffffff))
+
+    def test_crc32empty(self):
+        self.assertEqual(lzma.crc32(b"", 0), 0)
+        self.assertEqual(lzma.crc32(b"", 1), 1)
+        self.assertEqual(lzma.crc32(b"", 432), 432)
+
+    def test_penguins(self):
+        self.assertEqual(lzma.crc32(b"penguin", 0), 0x0e5c1a120)
+        self.assertEqual(lzma.crc32(b"penguin", 1), 0x43b6aa94)
+        self.assertEqual(lzma.crc32(b"penguin"), lzma.crc32(b"penguin", 0))
+
+    def test_crc32_unsigned(self):
+        foo = b'abcdefghijklmnop'
+        # explicitly test signed behavior
+        self.assertEqual(lzma.crc32(foo), 2486878355)
+        self.assertEqual(lzma.crc32(b'spam'), 1138425661)
+
+    def test_same_as_binascii_crc32(self):
+        foo = b'abcdefghijklmnop'
+        crc = 2486878355
+        self.assertEqual(binascii.crc32(foo), crc)
+        self.assertEqual(lzma.crc32(foo), crc)
+        self.assertEqual(binascii.crc32(b'spam'), lzma.crc32(b'spam'))
+
+
+# Issue #10276 - check that inputs >=4 GiB are handled correctly.
+class ChecksumBigBufferTestCase(unittest.TestCase):
+
+    @bigmemtest(size=_4G + 4, memuse=1, dry_run=False)
+    def test_big_buffer(self, size):
+        data = b"nyan" * (_1G + 1)
+        self.assertEqual(lzma.crc32(data), 1044521549)
+        self.assertEqual(zlib.adler32(data), 2256789997)
+
 
 class CompressorDecompressorTestCase(unittest.TestCase):
 

Lib/zipfile/__init__.py

@@ -28,6 +28,7 @@
 
 try:
     import lzma # We may need its compression method
+    crc32 = lzma.crc32
 except ImportError:
     lzma = None
 

Misc/NEWS.d/next/Library/2025-03-18-14-18-06.gh-issue-91349.Qrnmxt.rst

@@ -0,0 +1,3 @@
+Expose the crc32 function from the lzma library. It is faster than the crc32
+function from the zlib library. Update zipfile to detect and use lzma.crc32
+zlic.crc32 binascii.crc32, in order of preference.

Modules/_lzmamodule.c

@@ -1599,10 +1599,40 @@ lzma_exec(PyObject *module)
     return 0;
 }
 
+/*[clinic input]
+_lzma.crc32 -> unsigned_int
+
+    data: Py_buffer
+    value: unsigned_int(bitwise=True) = 0
+        Starting value of the checksum.
+    /
+
+Compute a CRC-32 checksum of data.
+
+The returned checksum is an integer.
+[clinic start generated code]*/
+
+static unsigned int
+_lzma_crc32_impl(PyObject *module, Py_buffer *data, unsigned int value)
+/*[clinic end generated code: output=fca7916d796faf8b input=bb623a169c14534f]*/
+{
+    /* Releasing the GIL for very small buffers is inefficient
+       and may lower performance */
+    if (data->len > 1024*5) {
+        Py_BEGIN_ALLOW_THREADS
+        value = lzma_crc32(data->buf, (size_t)data->len, (uint32_t)value);
+        Py_END_ALLOW_THREADS
+    } else {
+        value = lzma_crc32(data->buf, (size_t)data->len, (uint32_t)value);
+    }
+    return value;
+}
+
 static PyMethodDef lzma_methods[] = {
     _LZMA_IS_CHECK_SUPPORTED_METHODDEF
     _LZMA__ENCODE_FILTER_PROPERTIES_METHODDEF
     _LZMA__DECODE_FILTER_PROPERTIES_METHODDEF
+    _LZMA_CRC32_METHODDEF
     {NULL}
 };