Add const to function parameters

[sebpop]

Looks good to me.

[EricWF]

This change is ABI breaking because these functions are exported using explicit template instantiations, and because changing their signature changes the mangling.

Can you explain why this change is needed?

[hiraditya]

Adding const could help compiler, I do not have any specific performance numbers yet. So if this is too much trouble then we don't have to merge this.

[mclow.lists]

Absent I good motivation (i.e, a documented, significant performance change), I don't think we want this - not because it's not a reasonable change (it is!), but because it's an ABI break.

It's unfortunate the __atoms were not passed as const in the first place.
An alternate change would be to add a new local variable in these routines:

const CharT *__cAtoms = __atoms;

and then use __cAtoms instead of __atoms in the routines.

But we should determine if this is a win, code-gen wise.

[hiraditya]

Thank you for the feedback. This was supposed to be first out of two patches. I have posted the next patch here: https://reviews.llvm.org/D30268 which aims to remove copy of __src array each time a number is parsed. I can abandon this patch if we don't need to separate this from the other.

[hiraditya]

Merged with https://reviews.llvm.org/D30268

include/locale

 struct __num_get
     : protected __num_get_base
 {
     static string __stage2_int_prep(ios_base& __iob, _CharT* __atoms, _CharT& __thousands_sep);
     static string __stage2_float_prep(ios_base& __iob, _CharT* __atoms, _CharT& __decimal_point,
                                       _CharT& __thousands_sep);
     static int __stage2_int_loop(_CharT __ct, int __base, char* __a, char*& __a_end,
                   unsigned& __dc, _CharT __thousands_sep, const string& __grouping,
-                  unsigned* __g, unsigned*& __g_end, _CharT* __atoms);
+                  unsigned* __g, unsigned*& __g_end, const _CharT* __atoms);
     static int __stage2_float_loop(_CharT __ct, bool& __in_units, char& __exp,
                                    char* __a, char*& __a_end,
                                    _CharT __decimal_point, _CharT __thousands_sep,
                                    const string& __grouping, unsigned* __g,
-                                   unsigned*& __g_end, unsigned& __dc, _CharT* __atoms);
+                                   unsigned*& __g_end, unsigned& __dc, const _CharT* __atoms);
 };
 
 template <class _CharT>
 string
 __num_get<_CharT>::__stage2_int_prep(ios_base& __iob, _CharT* __atoms, _CharT& __thousands_sep)
 {
     locale __loc = __iob.getloc();
     use_facet<ctype<_CharT> >(__loc).widen(__src, __src + 26, __atoms);

     __thousands_sep = __np.thousands_sep();
     return __np.grouping();
 }
 
 template <class _CharT>
 int
 __num_get<_CharT>::__stage2_int_loop(_CharT __ct, int __base, char* __a, char*& __a_end,
                   unsigned& __dc, _CharT __thousands_sep, const string& __grouping,
-                  unsigned* __g, unsigned*& __g_end, _CharT* __atoms)
+                  unsigned* __g, unsigned*& __g_end, const _CharT* __atoms)
 {
     if (__a_end == __a && (__ct == __atoms[24] || __ct == __atoms[25]))
     {
         *__a_end++ = __ct == __atoms[24] ? '+' : '-';
         __dc = 0;
         return 0;
     }
     if (__grouping.size() != 0 && __ct == __thousands_sep)

     ++__dc;
     return 0;
 }
 
 template <class _CharT>
 int
 __num_get<_CharT>::__stage2_float_loop(_CharT __ct, bool& __in_units, char& __exp, char* __a, char*& __a_end,
                     _CharT __decimal_point, _CharT __thousands_sep, const string& __grouping,
-                    unsigned* __g, unsigned*& __g_end, unsigned& __dc, _CharT* __atoms)
+                    unsigned* __g, unsigned*& __g_end, unsigned& __dc, const _CharT* __atoms)
 {
     if (__ct == __decimal_point)
     {
         if (!__in_units)
             return -1;
         __in_units = false;
         *__a_end++ = '.';
         if (__grouping.size() != 0 && __g_end-__g < __num_get_buf_sz)