bpo-38687: Expose zlib 'adler32_combine' function to Python zlib module

Doc/library/zlib.rst

@@ -47,6 +47,11 @@ The available exception and functions in this module are:
       platforms, use ``adler32(data) & 0xffffffff``.
 
 
+.. function:: adler32_combine(adler_1, adler_2, len_2)
+
+   Combines two Adler-32 checksums *adler_1* and *adler_2* into one. *len_2* is the length of the string used to generate *adler_2*.
+
+
 .. function:: compress(data, /, level=-1)
 
    Compresses the bytes in *data*, returning a bytes object containing compressed data.

Lib/test/test_zlib.py

@@ -48,6 +48,9 @@ def test_adler32empty(self):
         self.assertEqual(zlib.adler32(b"", 1), 1)
         self.assertEqual(zlib.adler32(b"", 432), 432)
 
+    def test_adler32_combine(self):
+        self.assertEqual(zlib.adler32_combine(zlib.adler32(b"penguin"), zlib.adler32(b"banana"), len(b"banana")), 636028248)
+
     def test_penguins(self):
         self.assertEqual(zlib.crc32(b"penguin", 0), 0x0e5c1a120)
         self.assertEqual(zlib.crc32(b"penguin", 1), 0x43b6aa94)

Misc/ACKS

@@ -1896,3 +1896,4 @@ Robert Leenders
 Tim Hopper
 Dan Lidral-Porter
 Ngalim Siregar
+Callum Attryde

Modules/zlibmodule.c

@@ -1264,6 +1264,31 @@ zlib_adler32_impl(PyObject *module, Py_buffer *data, unsigned int value)
     return PyLong_FromUnsignedLong(value & 0xffffffffU);
 }
 
+/*[clinic input]
+zlib.adler32_combine
+
+    adler_1: unsigned_int(bitwise=True)
+        First checksum.
+    adler_2: unsigned_int(bitwise=True)
+        Second checksum.
+    len_2: unsigned_int(bitwise=True)
+        Length of the buffer used to generate the second checksum.
+    /
+
+Combine two Adler-32 Checksums into one.
+
+The returned checksum is an integer.
+[clinic start generated code]*/
+
+static PyObject *
+zlib_adler32_combine_impl(PyObject *module, unsigned int adler_1,
+                          unsigned int adler_2, unsigned int len_2)
+/*[clinic end generated code: output=af156f2b847877ae input=c436395ab679bbc2]*/
+{
+	unsigned long value = adler32_combine64(adler_1, adler_2, len_2);
+	return PyLong_FromUnsignedLong(value & 0xffffffffU);
+}
+
 /*[clinic input]
 zlib.crc32
 
@@ -1309,6 +1334,7 @@ zlib_crc32_impl(PyObject *module, Py_buffer *data, unsigned int value)
 static PyMethodDef zlib_methods[] =
 {
     ZLIB_ADLER32_METHODDEF
+    ZLIB_ADLER32_COMBINE_METHODDEF
     ZLIB_COMPRESS_METHODDEF
     ZLIB_COMPRESSOBJ_METHODDEF
     ZLIB_CRC32_METHODDEF
@@ -1351,6 +1377,7 @@ PyDoc_STRVAR(zlib_module_documentation,
 "zlib library, which is based on GNU zip.\n"
 "\n"
 "adler32(string[, start]) -- Compute an Adler-32 checksum.\n"
+"adler32_combine(adler1, adler2, len2) -- Combine two Adler-32 checksums.\n"
 "compress(data[, level]) -- Compress data, with compression level 0-9 or -1.\n"
 "compressobj([level[, ...]]) -- Return a compressor object.\n"
 "crc32(string[, start]) -- Compute a CRC-32 checksum.\n"