File python-gmpy2-mpfr421.patch of Package python-gmpy2

--- gmpy2-2.1.5/src/gmpy2_format.c.orig	2022-09-23 22:12:17.000000000 -0600
+++ gmpy2-2.1.5/src/gmpy2_format.c	2024-01-22 12:05:12.917508874 -0700
@@ -24,6 +24,10 @@
  * License along with GMPY2; if not, see <http://www.gnu.org/licenses/>    *
  * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
 
+#if MPFR_VERSION >= MPFR_VERSION_NUM(4,2,1)
+#define MPFR_SIGNED_NAN
+#endif
+
 PyDoc_STRVAR(GMPy_doc_mpz_format,
 "x.__format__(fmt) -> string\n\n"
 "Return a Python string by formatting mpz 'x' using the format string\n"
@@ -206,6 +210,7 @@ GMPy_MPFR_Format(PyObject *self, PyObjec
     int buflen;
     int seensign = 0, seenalign = 0, seendecimal = 0, seendigits = 0;
     int seenround = 0, seenconv = 0;
+    int skip = 0;
 
     if (!MPFR_Check(self)) {
         TYPE_ERROR("requires mpfr type");
@@ -318,6 +323,12 @@ GMPy_MPFR_Format(PyObject *self, PyObjec
 
     buflen = mpfr_asprintf(&buffer, mpfrfmt, MPFR(self));
 
+#ifdef MPFR_SIGNED_NAN
+    if ((mpfr_nan_p(MPFR(self)) && (buffer[0] == '-' || buffer[0] == '+')) ||
+        (mpfr_inf_p(MPFR(self)) && buffer[0] == '+'))
+        skip = 1;
+#endif
+
     /* If there isn't a decimal point in the output and the output
      * only consists of digits, then append .0 */
     if (strlen(buffer) == strspn(buffer, "+- 0123456789")) {
@@ -327,14 +338,14 @@ GMPy_MPFR_Format(PyObject *self, PyObjec
             return PyErr_NoMemory();
         }
         *newbuf = '\0';
-        strcat(newbuf, buffer);
+        strcat(newbuf, &buffer[skip]);
         strcat(newbuf, ".0");
         mpfr_free_str(buffer);
         mpfrstr = Py_BuildValue("s", newbuf);
         free(newbuf);
     }
     else {
-        mpfrstr = Py_BuildValue("s", buffer);
+        mpfrstr = Py_BuildValue("s", &buffer[skip]);
         mpfr_free_str(buffer);
     }
     if (!mpfrstr) {
@@ -385,6 +396,7 @@ GMPy_MPC_Format(PyObject *self, PyObject
     int rbuflen, ibuflen;
     int seensign = 0, seenalign = 0, seendecimal = 0, seendigits = 0;
     int seenround = 0, seenconv = 0, seenstyle = 0, mpcstyle = 0;
+    int realskip = 0, imagskip = 0;
 
     if (!MPC_Check(self)) {
         TYPE_ERROR("requires 'mpc' object");
@@ -537,6 +549,12 @@ GMPy_MPC_Format(PyObject *self, PyObject
     rbuflen = mpfr_asprintf(&realbuf, rfmt,
                            mpc_realref(MPC(self)));
 
+#ifdef MPFR_SIGNED_NAN
+    if ((mpfr_nan_p(mpc_realref(MPC(self))) && (realbuf[0] == '-' || realbuf[0] == '+')) ||
+        (mpfr_inf_p(mpc_realref(MPC(self))) && realbuf[0] == '+'))
+        realskip = 1;
+#endif
+
     if (rbuflen < 0) {
         mpfr_free_str(realbuf);
         SYSTEM_ERROR("Internal error in mpfr_asprintf");
@@ -560,6 +578,12 @@ GMPy_MPC_Format(PyObject *self, PyObject
     ibuflen = mpfr_asprintf(&imagbuf, ifmt,
                            mpc_imagref(MPC(self)));
 
+#ifdef MPFR_SIGNED_NAN
+    if ((mpfr_nan_p(mpc_imagref(MPC(self))) && (imagbuf[0] == '-' || imagbuf[0] == '+')) ||
+        (mpfr_inf_p(mpc_imagref(MPC(self))) && imagbuf[0] == '+'))
+        imagskip = 1;
+#endif
+
     if (ibuflen < 0) {
         mpfr_free_str(realbuf);
         mpfr_free_str(imagbuf);
@@ -580,7 +604,7 @@ GMPy_MPC_Format(PyObject *self, PyObject
     tempbuf[0] = '\00';
     if (mpcstyle)
         strcat(tempbuf, "(");
-    strcat(tempbuf, realbuf);
+    strcat(tempbuf, &realbuf[realskip]);
 
     /* If there isn't a decimal point in the output and the output
      * is short and only consists of digits, then append .0 */
@@ -599,7 +623,7 @@ GMPy_MPC_Format(PyObject *self, PyObject
             strcat(tempbuf, "+");
         }
     }
-    strcat(tempbuf, imagbuf);
+    strcat(tempbuf, &imagbuf[imagskip]);
     if (strlen(imagbuf) < 50 &&
         strlen(imagbuf) == strspn(imagbuf, "+- 0123456789")) {
         strcat(tempbuf, ".0");