Issue #7117: Prepare for backport of py3k float repr.

Add the Python/dtoa.c file containing the main algorithms;
add corresponding include file and include in Python.h;
include license information for Python/dtoa.c;
add dtoa.c and dtoa.h to Makefile.

Doc/license.rst

@@ -708,3 +708,35 @@ The :mod:`select` and contains the following notice for the kqueue interface::
   LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   SUCH DAMAGE.
+
+
+strtod and dtoa
+---------------
+
+The file :file:`Python/dtoa.c`, which supplies C functions dtoa and
+strtod for conversion of C doubles to and from strings, is derived
+from the file of the same name by David M. Gay, currently available
+from http://www.netlib.org/fp/.  The original file, as retrieved on
+March 16, 2009, contains the following copyright and licensing
+notice::
+
+   /****************************************************************
+    *
+    * The author of this software is David M. Gay.
+    *
+    * Copyright (c) 1991, 2000, 2001 by Lucent Technologies.
+    *
+    * Permission to use, copy, modify, and distribute this software for any
+    * purpose without fee is hereby granted, provided that this entire notice
+    * is included in all copies of any software which is or includes a copy
+    * or modification of this software and in all copies of the supporting
+    * documentation for such software.
+    *
+    * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR IMPLIED
+    * WARRANTY.  IN PARTICULAR, NEITHER THE AUTHOR NOR LUCENT MAKES ANY
+    * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE MERCHANTABILITY
+    * OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR PURPOSE.
+    *
+    ***************************************************************/
+
+

Include/Python.h

@@ -137,6 +137,7 @@
 #include "pyctype.h"
 #include "pystrtod.h"
 #include "pystrcmp.h"
+#include "dtoa.h"
 
 /* _Py_Mangle is defined in compile.c */
 PyAPI_FUNC(PyObject*) _Py_Mangle(PyObject *p, PyObject *name);

Include/dtoa.h

@@ -0,0 +1,15 @@
+#ifndef PY_NO_SHORT_FLOAT_REPR
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+PyAPI_FUNC(double) _Py_dg_strtod(const char *str, char **ptr);
+PyAPI_FUNC(char *) _Py_dg_dtoa(double d, int mode, int ndigits,
+                        int *decpt, int *sign, char **rve);
+PyAPI_FUNC(void) _Py_dg_freedtoa(char *s);
+
+
+#ifdef __cplusplus
+}
+#endif
+#endif

Makefile.pre.in

@@ -290,6 +290,7 @@ PYTHON_OBJS=	\
 		Python/getopt.o \
 		Python/pystrcmp.o \
 		Python/pystrtod.o \
+		Python/dtoa.o \
 		Python/formatter_unicode.o \
 		Python/formatter_string.o \
 		Python/$(DYNLOADFILE) \
@@ -606,6 +607,7 @@ PYTHON_HEADERS= \
 		Include/complexobject.h \
 		Include/descrobject.h \
 		Include/dictobject.h \
+		Include/dtoa.h \
 		Include/enumobject.h \
 		Include/errcode.h \
 		Include/eval.h \

PCbuild/pythoncore.vcproj

@@ -902,6 +902,10 @@
 				RelativePath="..\Include\pystrtod.h"
 				>
 			</File>
+			<File
+				RelativePath="..\Include\dtoa.h"
+				>
+			</File>
 			<File
 				RelativePath="..\Include\Python-ast.h"
 				>
@@ -1798,6 +1802,10 @@
 				RelativePath="..\Python\pystrtod.c"
 				>
 			</File>
+			<File
+				RelativePath="..\Python\dtoa.c"
+				>
+			</File>
 			<File
 				RelativePath="..\Python\Python-ast.c"
 				>