Create Strtod()

This commit creates my_strod() and a synonym, Strtod(), to emulate
strtod() using the most precise function known to us that is available
on the platform.  strtod() is not in K&R, but is in C90, so atof() may
be silently substituted instead on those few platforms without it.

This function also correctly handles locale issues, such as if the radix
character should be a dot or comma (or something else) depending on the
parent perl code is using locale or not, and which locale.

The symbol Perl_strtod continues to be defined on platforms which have
some version of strtod(), for backward compatibility, and can be called
as a function (or rather macro) but most applications should just use
Strtod() and not sweat the details.

This commit also fixes the problems with the prior commit:
    commit 4ac6fab20b8950ee14756c6f2438809c572082cd
     Author: Karl Williamson <khw@cpan.org>
     Date:   Mon Apr 15 11:10:31 2019 -0600

         PATCH: [perl #133945] Perl_strtod failures

         This commit wraps Perl_strtod() in macros that cause the proper
         radix character to be used.

1 files changed, 101 insertions, 2 deletions

diff --git a/numeric.c b/numeric.c
index 9ccb808a4a..d4e3493784 100644
--- a/numeric.c
+++ b/numeric.c
@@ -29,6 +29,105 @@ values, including such things as replacements for the OS's atof() function
 #define PERL_IN_NUMERIC_C
 #include "perl.h"
 
+#ifdef Perl_strtod
+
+PERL_STATIC_INLINE NV
+S_strtod(pTHX_ const char * const s, char ** e)
+{
+    DECLARATION_FOR_LC_NUMERIC_MANIPULATION;
+    NV result;
+
+    STORE_LC_NUMERIC_SET_TO_NEEDED();
+
+#  ifdef USE_QUADMATH
+
+    result = strtoflt128(s, e);
+
+#  elif defined(HAS_STRTOLD) && defined(HAS_LONG_DOUBLE)    \
+                             && defined(USE_LONG_DOUBLE)
+#    if defined(__MINGW64_VERSION_MAJOR)
+      /***********************************************
+       We are unable to use strtold because of
+        https://sourceforge.net/p/mingw-w64/bugs/711/
+        &
+        https://sourceforge.net/p/mingw-w64/bugs/725/
+
+       but __mingw_strtold is fine.
+      ***********************************************/
+
+    result = __mingw_strtold(s, e);
+
+#    else
+
+    result = strtold(s, e);
+
+#    endif
+#  elif defined(HAS_STRTOD)
+
+    result = strtod(s, e);
+
+#  endif
+
+    RESTORE_LC_NUMERIC();
+
+    return result;
+}
+
+#endif  /* #ifdef Perl_strtod */
+
+/*
+
+=for apidoc my_strtod
+
+This function is equivalent to the libc strtod() function, and is available
+even on platforms that lack plain strtod().  Its return value is the best
+available precision depending on platform capabilities and F<Configure>
+options.
+
+It properly handles the locale radix character, meaning it expects a dot except
+when called from within the scope of S<C<use locale>>, in which case the radix
+character should be that specified by the current locale.
+
+The synonym Strod() may be used instead.
+
+=cut
+
+*/
+
+NV
+my_strtod(const char * const s, char **e)
+{
+    dTHX;
+
+    PERL_ARGS_ASSERT_MY_STRTOD;
+
+#ifdef Perl_strtod
+
+    return S_strtod(aTHX_ s, e);
+
+#else
+
+    {
+        NV result;
+        char ** end_ptr = NULL;
+
+        *end_ptr = my_atof2(s, &result);
+        if (e) {
+            *e = *end_ptr;
+        }
+
+        if (! *end_ptr) {
+            result = 0.0;
+        }
+
+        return result;
+    }
+
+#endif
+
+}
+
+
 U32
 Perl_cast_ulong(NV f)
 {
@@ -1354,7 +1453,7 @@ S_my_atof_infnan(pTHX_ const char* s, bool negative, const char* send, NV* value
             }
 #endif
             assert(strNE(fake, "silence compiler warning"));
-            nv = Perl_strtod(fake, &endp);
+            nv = S_strtod(aTHX_ fake, &endp);
             if (fake != endp) {
 #ifdef NV_INF
                 if ((infnan & IS_NUMBER_INFINITY)) {
@@ -1460,7 +1559,7 @@ Perl_my_atof3(pTHX_ const char* orig, NV* value, const STRLEN len)
             s = copy + (s - orig);
         }
 
-        result[2] = Perl_strtod(s, &endp);
+        result[2] = S_strtod(aTHX_ s, &endp);
 
         /* If we created a copy, 'endp' is in terms of that.  Convert back to
          * the original */