StringTools: added CountFloatNumberChars function

1 files changed, 76 insertions, 0 deletions

diff --git a/Common/interface/StringTools.h b/Common/interface/StringTools.h
index cc6bc7b6..6b775891 100644
--- a/Common/interface/StringTools.h
+++ b/Common/interface/StringTools.h
@@ -181,4 +181,80 @@ inline std::string StrToLower(std::string str)
     return str;
 }
 
+inline bool IsNum(char c)
+{
+    return c >= '0' && c <= '9';
+}
+
+/// Returns the number of chararcters at the beginning of the string that form a
+/// floating point number.
+inline size_t CountFloatNumberChars(const char* str)
+{
+    if (str == nullptr)
+        return 0;
+
+    const auto* num_end = str;
+    const auto* c       = str;
+    if (*c == 0)
+        return 0;
+
+    if (*c == '+' || *c == '-')
+        ++c;
+
+    if (*c == 0)
+        return 0;
+
+    if (*c == '0' && IsNum(*(c + 1)))
+    {
+        // 01 is invalid
+        return c - str + 1;
+    }
+
+    while (IsNum(*c))
+        num_end = ++c;
+
+    if (*c == '.')
+    {
+        if (c != str && IsNum(c[-1]))
+        {
+            // . as well as +. or -. are not valid numbers, however 0., +0., and -0. are.
+            num_end = c + 1;
+        }
+
+        ++c;
+        while (IsNum(*c))
+            num_end = ++c;
+
+        if (*c == 'e' || *c == 'E')
+        {
+            if (c - str < 2 || !IsNum(c[-2]))
+            {
+                // .e as well as +.e are invalid
+                return num_end - str;
+            }
+        }
+    }
+    else if (*c == 'e' || *c == 'E')
+    {
+        if (c - str < 1 || !IsNum(c[-1]))
+        {
+            // e as well as e+1 are invalid
+            return num_end - str;
+        }
+    }
+
+    if (*c == 'e' || *c == 'E')
+    {
+        ++c;
+        if (*c != '+' && *c != '-')
+            return num_end - str;
+
+        ++c;
+        while (IsNum(*c))
+            num_end = ++c;
+    }
+
+    return num_end - str;
+}
+
 } // namespace Diligent