add mysql compatible function bit_length

Author: shenh062326

presto-docs/src/main/sphinx/functions/string.rst

@@ -28,6 +28,10 @@ String Functions
     some languages. Specifically, this will return incorrect results for
     Lithuanian, Turkish and Azeri.
 
+.. function:: bit_length(string) -> boolean
+
+    Returns the count of bits for the given ``string``.
+
 .. function:: chr(n) -> varchar
 
     Returns the Unicode code point ``n`` as a single character string.

presto-main/src/main/java/com/facebook/presto/operator/scalar/StringFunctions.java

@@ -104,6 +104,15 @@ public static long charLength(@LiteralParameter("x") long x, @SqlType("char(x)")
         return x;
     }
 
+    @Description("count of bits for the given string")
+    @ScalarFunction("bit_length")
+    @LiteralParameters("x")
+    @SqlType(StandardTypes.BIGINT)
+    public static long bitLength(@SqlType("varchar(x)") Slice slice)
+    {
+        return (long) slice.length() * 8;
+    }
+
     @Description("greedily removes occurrences of a pattern in a string")
     @ScalarFunction
     @LiteralParameters({"x", "y"})

presto-main/src/test/java/com/facebook/presto/operator/scalar/TestStringFunctions.java

@@ -136,6 +136,16 @@ public void testLength()
         assertFunction("LENGTH('\u4FE1\u5FF5,\u7231,\u5E0C\u671B')", BIGINT, 7L);
     }
 
+    @Test
+    public void testBitLength()
+    {
+        assertFunction("BIT_LENGTH('')", BIGINT, 0L);
+        assertFunction("BIT_LENGTH('hello')", BIGINT, 40L);
+        // Test bit_length for non-ASCII
+        assertFunction("BIT_LENGTH('hell o\u00EF')", BIGINT, 64L);
+        assertFunction("BIT_LENGTH('中123')", BIGINT, 48L);
+    }
+
     @Test
     public void testCharLength()
     {