Add initcap prototype / tests

docs/en/sql-reference/functions/string-functions.md

@@ -1253,3 +1253,7 @@ Result:
 │ A240             │
 └──────────────────┘
 ```
+
+## initcap
+
+Convert the first letter of each word to upper case and the rest to lower case. Words are sequences of alphanumeric characters separated by non-alphanumeric characters.

docs/ru/sql-reference/functions/string-functions.md

@@ -1113,3 +1113,7 @@ A text with tags .
 The content within <b>CDATA</b>
 Do Nothing for 2 Minutes 2:00 &nbsp;
 ```
+
+## initcap {#initcap}
+
+Переводит первую букву каждого слова в строке в верхний регистр, а остальные — в нижний. Словами считаются последовательности алфавитно-цифровых символов, разделённые любыми другими символами.

src/Functions/initcap.cpp

@@ -0,0 +1,78 @@
+#include <Functions/FunctionFactory.h>
+#include <Functions/FunctionStringToString.h>
+
+namespace DB
+{
+namespace
+{
+
+struct InitcapImpl
+{
+    static void vector(const ColumnString::Chars & data,
+        const ColumnString::Offsets & offsets,
+        ColumnString::Chars & res_data,
+        ColumnString::Offsets & res_offsets)
+    {
+        res_data.resize(data.size());
+        res_offsets.assign(offsets);
+        array(data.data(), data.data() + data.size(), res_data.data());
+    }
+
+    static void vectorFixed(const ColumnString::Chars & data, size_t /*n*/, ColumnString::Chars & res_data)
+    {
+        res_data.resize(data.size());
+        array(data.data(), data.data() + data.size(), res_data.data());
+    }
+
+private:
+    static void array(const UInt8 * src, const UInt8 * src_end, UInt8 * dst)
+    {
+        const auto flip_case_mask = 'A' ^ 'a';
+
+        auto is_lower_alpha = [](UInt8 c) { return c >= 'a' && c <= 'z'; };
+        auto is_upper_alpha = [](UInt8 c) { return c >= 'A' && c <= 'Z'; };
+        //auto is_digit = [](UInt8 c) { return c >= '0' && c <= '9'; };
+
+        bool prev_is_alpha = false;
+
+        for (; src < src_end; ++src, ++dst)
+        {
+            bool lower = is_lower_alpha(*src);
+            bool is_alpha = lower || is_upper_alpha(*src);
+            if (!is_alpha)
+            {
+                *dst = *src;
+            }
+            else if (!prev_is_alpha)
+            {
+                if (lower)
+                    *dst = *src ^ flip_case_mask;
+                else
+                    *dst = *src;
+            }
+            else
+            {
+                if (!lower)
+                    *dst = *src ^ flip_case_mask;
+                else
+                    *dst = *src;
+            }
+            prev_is_alpha = is_alpha;
+        }
+    }
+};
+
+struct NameInitcap
+{
+    static constexpr auto name = "initcap";
+};
+using FunctionInitcap = FunctionStringToString<InitcapImpl, NameInitcap>;
+
+}
+
+REGISTER_FUNCTION(Initcap)
+{
+    factory.registerFunction<FunctionInitcap>({}, FunctionFactory::CaseInsensitive);
+}
+
+}

tests/queries/0_stateless/02810_initcap.reference

@@ -0,0 +1,6 @@
+
+Hello
+Hello
+Hello World
+Yeah, Well, I`M Gonna Go Build My Own Theme Park
+Crc32ieee Is Best Function

tests/queries/0_stateless/02810_initcap.sql

@@ -0,0 +1,6 @@
+select initcap('');
+select initcap('Hello');
+select initcap('hello');
+select initcap('hello world');
+select initcap('yeah, well, i`m gonna go build my own theme park');
+select initcap('CRC32IEEE is best function');