gh-61103: Support double complex (_Complex) type in ctypes (#120894)

Example:

```pycon
>>> import ctypes
>>> ctypes.__STDC_IEC_559_COMPLEX__
1
>>> libm = ctypes.CDLL('libm.so.6')
>>> libm.clog.argtypes = [ctypes.c_double_complex]
>>> libm.clog.restype = ctypes.c_double_complex
>>> libm.clog(1+1j)
(0.34657359027997264+0.7853981633974483j)
```

Co-authored-by: Nice Zombies <nineteendo19d0@gmail.com>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>
Co-authored-by: Victor Stinner <vstinner@python.org>

Modules/_complex.h

@@ -0,0 +1,34 @@
+/* Workarounds for buggy complex number arithmetic implementations. */
+
+#ifndef Py_HAVE_C_COMPLEX
+#  error "this header file should only be included if Py_HAVE_C_COMPLEX is defined"
+#endif
+
+#include <complex.h>
+
+/* Other compilers (than clang), that claims to
+   implement C11 *and* define __STDC_IEC_559_COMPLEX__ - don't have
+   issue with CMPLX().  This is specific to glibc & clang combination:
+   https://sourceware.org/bugzilla/show_bug.cgi?id=26287
+
+   Here we fallback to using __builtin_complex(), available in clang
+   v12+.  Else CMPLX implemented following C11 6.2.5p13: "Each complex type
+   has the same representation and alignment requirements as an array
+   type containing exactly two elements of the corresponding real type;
+   the first element is equal to the real part, and the second element
+   to the imaginary part, of the complex number.
+ */
+#if !defined(CMPLX)
+#  if defined(__clang__) && __has_builtin(__builtin_complex)
+#    define CMPLX(x, y) __builtin_complex ((double) (x), (double) (y))
+#  else
+static inline double complex
+CMPLX(double real, double imag)
+{
+    double complex z;
+    ((double *)(&z))[0] = real;
+    ((double *)(&z))[1] = imag;
+    return z;
+}
+#  endif
+#endif

Modules/_ctypes/_ctypes.c

@@ -1750,7 +1750,11 @@ class _ctypes.c_void_p "PyObject *" "clinic_state_sub()->PyCSimpleType_Type"
 [clinic start generated code]*/
 /*[clinic end generated code: output=da39a3ee5e6b4b0d input=dd4d9646c56f43a9]*/
 
+#if defined(Py_HAVE_C_COMPLEX) && defined(FFI_TARGET_HAS_COMPLEX_TYPE)
+static const char SIMPLE_TYPE_CHARS[] = "cbBhHiIlLdCfuzZqQPXOv?g";
+#else
 static const char SIMPLE_TYPE_CHARS[] = "cbBhHiIlLdfuzZqQPXOv?g";
+#endif
 
 /*[clinic input]
 _ctypes.c_wchar_p.from_param as c_wchar_p_from_param
@@ -2226,7 +2230,17 @@ PyCSimpleType_init(PyObject *self, PyObject *args, PyObject *kwds)
         goto error;
     }
 
-    stginfo->ffi_type_pointer = *fmt->pffi_type;
+    if (!fmt->pffi_type->elements) {
+        stginfo->ffi_type_pointer = *fmt->pffi_type;
+    }
+    else {
+        stginfo->ffi_type_pointer.size = fmt->pffi_type->size;
+        stginfo->ffi_type_pointer.alignment = fmt->pffi_type->alignment;
+        stginfo->ffi_type_pointer.type = fmt->pffi_type->type;
+        stginfo->ffi_type_pointer.elements = PyMem_Malloc(2 * sizeof(ffi_type));
+        memcpy(stginfo->ffi_type_pointer.elements,
+               fmt->pffi_type->elements, 2 * sizeof(ffi_type));
+    }
     stginfo->align = fmt->pffi_type->alignment;
     stginfo->length = 0;
     stginfo->size = fmt->pffi_type->size;

Modules/_ctypes/_ctypes_test.c

@@ -13,6 +13,12 @@
 
 #include <Python.h>
 
+#include <ffi.h>                  // FFI_TARGET_HAS_COMPLEX_TYPE
+
+#if defined(Py_HAVE_C_COMPLEX) && defined(FFI_TARGET_HAS_COMPLEX_TYPE)
+#  include "../_complex.h"        // csqrt()
+#  undef I                        // for _ctypes_test_generated.c.h
+#endif
 #include <stdio.h>                // printf()
 #include <stdlib.h>               // qsort()
 #include <string.h>               // memset()
@@ -443,6 +449,13 @@ EXPORT(double) my_sqrt(double a)
     return sqrt(a);
 }
 
+#if defined(Py_HAVE_C_COMPLEX) && defined(FFI_TARGET_HAS_COMPLEX_TYPE)
+EXPORT(double complex) my_csqrt(double complex a)
+{
+    return csqrt(a);
+}
+#endif
+
 EXPORT(void) my_qsort(void *base, size_t num, size_t width, int(*compare)(const void*, const void*))
 {
     qsort(base, num, width, compare);

Modules/_ctypes/callproc.c

@@ -105,6 +105,10 @@ module _ctypes
 #include "pycore_global_objects.h"// _Py_ID()
 #include "pycore_traceback.h"     // _PyTraceback_Add()
 
+#if defined(Py_HAVE_C_COMPLEX) && defined(FFI_TARGET_HAS_COMPLEX_TYPE)
+#include "../_complex.h"          // complex
+#endif
+
 #include "clinic/callproc.c.h"
 
 #define CTYPES_CAPSULE_NAME_PYMEM "_ctypes pymem"
@@ -651,6 +655,9 @@ union result {
     double d;
     float f;
     void *p;
+#if defined(Py_HAVE_C_COMPLEX) && defined(FFI_TARGET_HAS_COMPLEX_TYPE)
+    double complex C;
+#endif
 };
 
 struct argument {

Modules/_ctypes/cfield.c

@@ -14,6 +14,9 @@
 #include <ffi.h>
 #include "ctypes.h"
 
+#if defined(Py_HAVE_C_COMPLEX) && defined(FFI_TARGET_HAS_COMPLEX_TYPE)
+#  include "../_complex.h"        // complex
+#endif
 
 #define CTYPES_CFIELD_CAPSULE_NAME_PYMEM "_ctypes/cfield.c pymem"
 
@@ -1087,6 +1090,30 @@ d_get(void *ptr, Py_ssize_t size)
     return PyFloat_FromDouble(val);
 }
 
+#if defined(Py_HAVE_C_COMPLEX) && defined(FFI_TARGET_HAS_COMPLEX_TYPE)
+static PyObject *
+C_set(void *ptr, PyObject *value, Py_ssize_t size)
+{
+    Py_complex c = PyComplex_AsCComplex(value);
+
+    if (c.real == -1 && PyErr_Occurred()) {
+        return NULL;
+    }
+    double complex x = CMPLX(c.real, c.imag);
+    memcpy(ptr, &x, sizeof(x));
+    _RET(value);
+}
+
+static PyObject *
+C_get(void *ptr, Py_ssize_t size)
+{
+    double complex x;
+
+    memcpy(&x, ptr, sizeof(x));
+    return PyComplex_FromDoubles(creal(x), cimag(x));
+}
+#endif
+
 static PyObject *
 d_set_sw(void *ptr, PyObject *value, Py_ssize_t size)
 {
@@ -1592,6 +1619,9 @@ static struct fielddesc formattable[] = {
     { 'B', B_set, B_get, NULL},
     { 'c', c_set, c_get, NULL},
     { 'd', d_set, d_get, NULL, d_set_sw, d_get_sw},
+#if defined(Py_HAVE_C_COMPLEX) && defined(FFI_TARGET_HAS_COMPLEX_TYPE)
+    { 'C', C_set, C_get, NULL},
+#endif
     { 'g', g_set, g_get, NULL},
     { 'f', f_set, f_get, NULL, f_set_sw, f_get_sw},
     { 'h', h_set, h_get, NULL, h_set_sw, h_get_sw},
@@ -1642,6 +1672,9 @@ _ctypes_init_fielddesc(void)
         case 'B': fd->pffi_type = &ffi_type_uchar; break;
         case 'c': fd->pffi_type = &ffi_type_schar; break;
         case 'd': fd->pffi_type = &ffi_type_double; break;
+#if defined(Py_HAVE_C_COMPLEX) && defined(FFI_TARGET_HAS_COMPLEX_TYPE)
+        case 'C': fd->pffi_type = &ffi_type_complex_double; break;
+#endif
         case 'g': fd->pffi_type = &ffi_type_longdouble; break;
         case 'f': fd->pffi_type = &ffi_type_float; break;
         case 'h': fd->pffi_type = &ffi_type_sshort; break;

Modules/_ctypes/ctypes.h

@@ -2,9 +2,15 @@
 #   include <alloca.h>
 #endif
 
+#include <ffi.h>                  // FFI_TARGET_HAS_COMPLEX_TYPE
+
 #include "pycore_moduleobject.h"  // _PyModule_GetState()
 #include "pycore_typeobject.h"    // _PyType_GetModuleState()
 
+#if defined(Py_HAVE_C_COMPLEX) && defined(FFI_TARGET_HAS_COMPLEX_TYPE)
+#   include "../_complex.h"       // complex
+#endif
+
 #ifndef MS_WIN32
 #define max(a, b) ((a) > (b) ? (a) : (b))
 #define min(a, b) ((a) < (b) ? (a) : (b))
@@ -393,6 +399,9 @@ struct tagPyCArgObject {
         double d;
         float f;
         void *p;
+#if defined(Py_HAVE_C_COMPLEX) && defined(FFI_TARGET_HAS_COMPLEX_TYPE)
+        double complex C;
+#endif
     } value;
     PyObject *obj;
     Py_ssize_t size; /* for the 'V' tag */