Issue #29004: Document binascii.crc_hqx() implements CRC-CCITT

Doc/library/binascii.rst

@@ -115,8 +115,10 @@ The :mod:`binascii` module defines the following functions:
 
 .. function:: crc_hqx(data, value)
 
-   Compute the binhex4 crc value of *data*, starting with *value* as the
-   initial crc, and return the result.
+   Compute a 16-bit CRC value of *data*, starting with *value* as the
+   initial CRC, and return the result.  This uses the CRC-CCITT polynomial
+   *x*:sup:`16` + *x*:sup:`12` + *x*:sup:`5` + 1, often represented as
+   0x1021.  This CRC is used in the binhex4 format.
 
 
 .. function:: crc32(data[, value])

Modules/binascii.c

@@ -915,12 +915,12 @@ binascii.crc_hqx -> unsigned_int
     crc: unsigned_int(bitwise=True)
     /
 
-Compute hqx CRC incrementally.
+Compute CRC-CCITT incrementally.
 [clinic start generated code]*/
 
 static unsigned int
 binascii_crc_hqx_impl(PyObject *module, Py_buffer *data, unsigned int crc)
-/*[clinic end generated code: output=8ec2a78590d19170 input=add8c53712ccceda]*/
+/*[clinic end generated code: output=8ec2a78590d19170 input=f18240ff8c705b79]*/
 {
     unsigned char *bin_data;
     Py_ssize_t len;

Modules/clinic/binascii.c.h

@@ -246,7 +246,7 @@ PyDoc_STRVAR(binascii_crc_hqx__doc__,
 "crc_hqx($module, data, crc, /)\n"
 "--\n"
 "\n"
-"Compute hqx CRC incrementally.");
+"Compute CRC-CCITT incrementally.");
 
 #define BINASCII_CRC_HQX_METHODDEF    \
     {"crc_hqx", (PyCFunction)binascii_crc_hqx, METH_VARARGS, binascii_crc_hqx__doc__},
@@ -516,4 +516,4 @@ exit:
 
     return return_value;
 }
-/*[clinic end generated code: output=51173fc9718a5edc input=a9049054013a1b77]*/
+/*[clinic end generated code: output=6d70d5edd9373d92 input=a9049054013a1b77]*/