Issue #7652: Integrate the decimal floating point libmpdec library to speed

up the decimal module. Performance gains of the new C implementation are
between 12x and 80x, depending on the application.

setup.py

@@ -1342,6 +1342,9 @@ class PyBuildExt(build_ext):
             exts.append(Extension('_codecs_%s' % loc,
                                   ['cjkcodecs/_codecs_%s.c' % loc]))
 
+        # Stefan Krah's _decimal module
+        exts.append(self._decimal_ext())
+
         # Thomas Heller's _ctypes module
         self.detect_ctypes(inc_dirs, lib_dirs)
 
@@ -1792,6 +1795,116 @@ class PyBuildExt(build_ext):
             ext.libraries.append(ffi_lib)
             self.use_system_libffi = True
 
+    def _decimal_ext(self):
+        sources = [
+          '_decimal/_decimal.c',
+          '_decimal/libmpdec/basearith.c',
+          '_decimal/libmpdec/constants.c',
+          '_decimal/libmpdec/context.c',
+          '_decimal/libmpdec/convolute.c',
+          '_decimal/libmpdec/crt.c',
+          '_decimal/libmpdec/difradix2.c',
+          '_decimal/libmpdec/fnt.c',
+          '_decimal/libmpdec/fourstep.c',
+          '_decimal/libmpdec/io.c',
+          '_decimal/libmpdec/memory.c',
+          '_decimal/libmpdec/mpdecimal.c',
+          '_decimal/libmpdec/numbertheory.c',
+          '_decimal/libmpdec/sixstep.c',
+          '_decimal/libmpdec/transpose.c',
+        ]
+        depends = [
+          '_decimal/docstrings.h',
+          '_decimal/libmpdec/basearith.h',
+          '_decimal/libmpdec/bits.h',
+          '_decimal/libmpdec/constants.h',
+          '_decimal/libmpdec/convolute.h',
+          '_decimal/libmpdec/crt.h',
+          '_decimal/libmpdec/difradix2.h',
+          '_decimal/libmpdec/fnt.h',
+          '_decimal/libmpdec/fourstep.h',
+          '_decimal/libmpdec/io.h',
+          '_decimal/libmpdec/memory.h',
+          '_decimal/libmpdec/mpdecimal.h',
+          '_decimal/libmpdec/numbertheory.h',
+          '_decimal/libmpdec/sixstep.h',
+          '_decimal/libmpdec/transpose.h',
+          '_decimal/libmpdec/typearith.h',
+          '_decimal/libmpdec/umodarith.h',
+        ]
+        config = {
+          'x64':     [('CONFIG_64','1'), ('ASM','1')],
+          'uint128': [('CONFIG_64','1'), ('ANSI','1'), ('HAVE_UINT128_T','1')],
+          'ansi64':  [('CONFIG_64','1'), ('ANSI','1')],
+          'ppro':    [('CONFIG_32','1'), ('PPRO','1'), ('ASM','1')],
+          'ansi32':  [('CONFIG_32','1'), ('ANSI','1')],
+          'ansi-legacy': [('CONFIG_32','1'), ('ANSI','1'),
+                          ('LEGACY_COMPILER','1')],
+          'universal':   [('UNIVERSAL','1')]
+        }
+
+        include_dirs = ['./Modules/_decimal/libmpdec']
+        extra_compile_args = []
+        undef_macros=['NDEBUG']
+
+        platform = self.get_platform()
+        cc = sysconfig.get_config_var('CC')
+        sizeof_size_t = sysconfig.get_config_var('SIZEOF_SIZE_T')
+        machine = os.environ.get('PYTHON_DECIMAL_WITH_MACHINE')
+
+        if machine:
+            # Override automatic configuration to facilitate testing.
+            define_macros = config[machine]
+        elif platform == 'darwin':
+            # Universal here means: build with the same options Python
+            # was built with.
+            define_macros = config['universal']
+        elif sizeof_size_t == 8:
+            if sysconfig.get_config_var('HAVE_GCC_ASM_FOR_X64'):
+                define_macros = config['x64']
+            elif sysconfig.get_config_var('HAVE_GCC_UINT128_T'):
+                define_macros = config['uint128']
+            else:
+                define_macros = config['ansi64']
+        elif sizeof_size_t == 4:
+            ppro = sysconfig.get_config_var('HAVE_GCC_ASM_FOR_X87')
+            if ppro and ('gcc' in cc or 'clang' in cc) and \
+               not 'sunos' in platform:
+                # solaris: problems with register allocation.
+                # icc >= 11.0 works as well.
+                define_macros = config['ppro']
+            else:
+                define_macros = config['ansi32']
+        else:
+            raise DistutilsError("_decimal: unsupported architecture")
+
+        # Workarounds for toolchain bugs:
+        if sysconfig.get_config_var('HAVE_IPA_PURE_CONST_BUG'):
+            # Some versions of gcc miscompile inline asm:
+            # http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46491
+            # http://gcc.gnu.org/ml/gcc/2010-11/msg00366.html
+            extra_compile_args.append('-fno-ipa-pure-const')
+        if sysconfig.get_config_var('HAVE_GLIBC_MEMMOVE_BUG'):
+            # _FORTIFY_SOURCE wrappers for memmove and bcopy are incorrect:
+            # http://sourceware.org/ml/libc-alpha/2010-12/msg00009.html
+            undef_macros.append('_FORTIFY_SOURCE')
+
+        # Faster version without thread local contexts:
+        if not sysconfig.get_config_var('WITH_THREAD'):
+            define_macros.append(('WITHOUT_THREADS', 1))
+
+        # Uncomment for extra functionality:
+        #define_macros.append(('EXTRA_FUNCTIONALITY', 1))
+        ext = Extension (
+            '_decimal',
+            include_dirs=include_dirs,
+            define_macros=define_macros,
+            undef_macros=undef_macros,
+            extra_compile_args=extra_compile_args,
+            sources=sources,
+            depends=depends
+        )
+        return ext
 
 class PyBuildInstall(install):
     # Suppress the warning about installation into the lib_dynload