epee: speed up parse_hexstr_to_binbuff a little

contrib/epee/include/string_tools.h

@@ -59,6 +59,26 @@
 #pragma comment (lib, "Rpcrt4.lib")
 #endif
 
+static const constexpr unsigned char isx[256] =
+{
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+    0,    1,    2,    3,    4,    5,    6,    7,    8,    9, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff,   10,   11,   12,   13,   14,   15, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff,   10,   11,   12,   13,   14,   15, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+ 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+};
+
 namespace epee
 {
 namespace string_tools
@@ -98,30 +118,30 @@ namespace string_tools
   }
   //----------------------------------------------------------------------------
   template<class CharT>
-  bool parse_hexstr_to_binbuff(const std::basic_string<CharT>& s, std::basic_string<CharT>& res, bool allow_partial_byte = false)
+  bool parse_hexstr_to_binbuff(const std::basic_string<CharT>& s, std::basic_string<CharT>& res)
   {
     res.clear();
-    if (!allow_partial_byte && (s.size() & 1))
+    if (s.size() & 1)
       return false;
     try
     {
-      long v = 0;
-      for(size_t i = 0; i < (s.size() + 1) / 2; i++)
+      res.resize(s.size() / 2);
+      unsigned char *dst = (unsigned char *)res.data();
+      const unsigned char *src = (const unsigned char *)s.data();
+      for(size_t i = 0; i < s.size(); i += 2)
       {
-        CharT byte_str[3];
-        size_t copied = s.copy(byte_str, 2, 2 * i);
-        byte_str[copied] = CharT(0);
-        CharT* endptr;
-        v = strtoul(byte_str, &endptr, 16);
-        if (v < 0 || 0xFF < v || endptr != byte_str + copied)
-        {
-          return false;
-        }
-        res.push_back(static_cast<unsigned char>(v));
+        int tmp = *src++;
+        tmp = isx[tmp];
+        if (tmp == 0xff) return false;
+        int t2 = *src++;
+        t2 = isx[t2];
+        if (t2 == 0xff) return false;
+        *dst++ = (tmp << 4) | t2;
       }
 
       return true;
-    }catch(...)
+    }
+    catch(...)
     {
       return false;
     }