Index: libcxx/src/string.cpp
===================================================================
--- libcxx/src/string.cpp
+++ libcxx/src/string.cpp
@@ -348,10 +348,21 @@
 
 // as_string
 
+template<typename S, typename P, typename V>
+inline
+S
+i_to_string(P sprintf_like, const typename S::value_type* fmt, V a)
+{
+    constexpr size_t size = 4 * sizeof(V) + 1; // +1 for null char from swprintf
+    typename S::value_type buf[size] = {};
+    const int len = sprintf_like(buf, size, fmt, a);
+    return S(buf, buf + len);
+}
+
 template<typename S, typename P, typename V >
 inline
 S
-as_string(P sprintf_like, S s, const typename S::value_type* fmt, V a)
+f_to_string(P sprintf_like, S s, const typename S::value_type* fmt, V a)
 {
     typedef typename S::size_type size_type;
     size_type available = s.size();
@@ -375,47 +386,21 @@
     return s;
 }
 
-template <class S, class V, bool = is_floating_point<V>::value>
-struct initial_string;
-
-template <class V, bool b>
-struct initial_string<string, V, b>
-{
-    string
-    operator()() const
-    {
-        string s;
-        s.resize(s.capacity());
-        return s;
-    }
-};
-
-template <class V>
-struct initial_string<wstring, V, false>
+inline
+string initial_string()
 {
-    wstring
-    operator()() const
-    {
-        const size_t n = (numeric_limits<unsigned long long>::digits / 3)
-          + ((numeric_limits<unsigned long long>::digits % 3) != 0)
-          + 1;
-        wstring s(n, wchar_t());
-        s.resize(s.capacity());
-        return s;
-    }
-};
+    string s;
+    s.resize(s.capacity());
+    return s;
+}
 
-template <class V>
-struct initial_string<wstring, V, true>
+inline
+wstring initial_wstring()
 {
-    wstring
-    operator()() const
-    {
-        wstring s(20, wchar_t());
-        s.resize(s.capacity());
-        return s;
-    }
-};
+    wstring s(20, wchar_t());
+    s.resize(s.capacity());
+    return s;
+}
 
 typedef int (*wide_printf)(wchar_t* __restrict, size_t, const wchar_t*__restrict, ...);
 
@@ -434,91 +419,91 @@
 
 string to_string(int val)
 {
-    return as_string(snprintf, initial_string<string, int>()(), "%d", val);
+    return i_to_string<string>(snprintf, "%d", val);
 }
 
 string to_string(unsigned val)
 {
-    return as_string(snprintf, initial_string<string, unsigned>()(), "%u", val);
+    return i_to_string<string>(snprintf, "%u", val);
 }
 
 string to_string(long val)
 {
-    return as_string(snprintf, initial_string<string, long>()(), "%ld", val);
+    return i_to_string<string>(snprintf, "%ld", val);
 }
 
 string to_string(unsigned long val)
 {
-    return as_string(snprintf, initial_string<string, unsigned long>()(), "%lu", val);
+    return i_to_string<string>(snprintf, "%lu", val);
 }
 
 string to_string(long long val)
 {
-    return as_string(snprintf, initial_string<string, long long>()(), "%lld", val);
+    return i_to_string<string>(snprintf, "%lld", val);
 }
 
 string to_string(unsigned long long val)
 {
-    return as_string(snprintf, initial_string<string, unsigned long long>()(), "%llu", val);
+    return i_to_string<string>(snprintf, "%llu", val);
 }
 
 string to_string(float val)
 {
-    return as_string(snprintf, initial_string<string, float>()(), "%f", val);
+    return f_to_string(snprintf, initial_string(), "%f", val);
 }
 
 string to_string(double val)
 {
-    return as_string(snprintf, initial_string<string, double>()(), "%f", val);
+    return f_to_string(snprintf, initial_string(), "%f", val);
 }
 
 string to_string(long double val)
 {
-    return as_string(snprintf, initial_string<string, long double>()(), "%Lf", val);
+    return f_to_string(snprintf, initial_string(), "%Lf", val);
 }
 
 wstring to_wstring(int val)
 {
-    return as_string(get_swprintf(), initial_string<wstring, int>()(), L"%d", val);
+    return i_to_string<wstring>(get_swprintf(), L"%d", val);
 }
 
 wstring to_wstring(unsigned val)
 {
-    return as_string(get_swprintf(), initial_string<wstring, unsigned>()(), L"%u", val);
+    return i_to_string<wstring>(get_swprintf(), L"%u", val);
 }
 
 wstring to_wstring(long val)
 {
-    return as_string(get_swprintf(), initial_string<wstring, long>()(), L"%ld", val);
+    return i_to_string<wstring>(get_swprintf(), L"%ld", val);
 }
 
 wstring to_wstring(unsigned long val)
 {
-    return as_string(get_swprintf(), initial_string<wstring, unsigned long>()(), L"%lu", val);
+    return i_to_string<wstring>(get_swprintf(), L"%lu", val);
 }
 
 wstring to_wstring(long long val)
 {
-    return as_string(get_swprintf(), initial_string<wstring, long long>()(), L"%lld", val);
+    return i_to_string<wstring>(get_swprintf(), L"%lld", val);
 }
 
 wstring to_wstring(unsigned long long val)
 {
-    return as_string(get_swprintf(), initial_string<wstring, unsigned long long>()(), L"%llu", val);
+    return i_to_string<wstring>(get_swprintf(), L"%llu", val);
 }
 
 wstring to_wstring(float val)
 {
-    return as_string(get_swprintf(), initial_string<wstring, float>()(), L"%f", val);
+    return f_to_string(get_swprintf(), initial_wstring(), L"%f", val);
 }
 
 wstring to_wstring(double val)
 {
-    return as_string(get_swprintf(), initial_string<wstring, double>()(), L"%f", val);
+    return f_to_string(get_swprintf(), initial_wstring(), L"%f", val);
 }
 
 wstring to_wstring(long double val)
 {
-    return as_string(get_swprintf(), initial_string<wstring, long double>()(), L"%Lf", val);
+    return f_to_string(get_swprintf(), initial_wstring(), L"%Lf", val);
 }
 _LIBCPP_END_NAMESPACE_STD