sql: add get_bit() and set_bit() builtin functions

Resolve cockroachdb#45851

This commit adds builtin function get_bit() and set_bit(),
along with thier respective testcases.

Characteristics of the above builtin functions are:
    * get_bit() allows us to extracts a bit at given index in
      the bit array.
    * set_bit() enable us updates a bit at given index in the
      bit array.

Release justification: first good issue, adding builtin functions.

Release note (sql change): This PR is introduced to add get_bits()
and set_bit() builtin functions.

docs/generated/sql/functions.md

@@ -865,6 +865,8 @@ has no relationship with the commit order of concurrent transactions.</p>
 </span></td></tr>
 <tr><td><a name="from_uuid"></a><code>from_uuid(val: <a href="bytes.html">bytes</a>) &rarr; <a href="string.html">string</a></code></td><td><span class="funcdesc"><p>Converts the byte string representation of a UUID to its character string representation.</p>
 </span></td></tr>
+<tr><td><a name="get_bit"></a><code>get_bit(bit_string: varbit, index: <a href="int.html">int</a>) &rarr; <a href="int.html">int</a></code></td><td><span class="funcdesc"><p>Extracts a bit at given index in the bit array</p>
+</span></td></tr>
 <tr><td><a name="initcap"></a><code>initcap(val: <a href="string.html">string</a>) &rarr; <a href="string.html">string</a></code></td><td><span class="funcdesc"><p>Capitalizes the first letter of <code>val</code>.</p>
 </span></td></tr>
 <tr><td><a name="left"></a><code>left(input: <a href="bytes.html">bytes</a>, return_set: <a href="int.html">int</a>) &rarr; <a href="bytes.html">bytes</a></code></td><td><span class="funcdesc"><p>Returns the first <code>return_set</code> bytes from <code>input</code>.</p>
@@ -1007,6 +1009,8 @@ has no relationship with the commit order of concurrent transactions.</p>
 </span></td></tr>
 <tr><td><a name="rtrim"></a><code>rtrim(val: <a href="string.html">string</a>) &rarr; <a href="string.html">string</a></code></td><td><span class="funcdesc"><p>Removes all spaces from the end (right-hand side) of <code>val</code>.</p>
 </span></td></tr>
+<tr><td><a name="set_bit"></a><code>set_bit(bit_string: varbit, index: <a href="int.html">int</a>, to_set: <a href="int.html">int</a>) &rarr; varbit</code></td><td><span class="funcdesc"><p>Updates a bit at given index in the bit array</p>
+</span></td></tr>
 <tr><td><a name="sha1"></a><code>sha1(<a href="bytes.html">bytes</a>...) &rarr; <a href="string.html">string</a></code></td><td><span class="funcdesc"><p>Calculates the SHA1 hash value of a set of values.</p>
 </span></td></tr>
 <tr><td><a name="sha1"></a><code>sha1(<a href="string.html">string</a>...) &rarr; <a href="string.html">string</a></code></td><td><span class="funcdesc"><p>Calculates the SHA1 hash value of a set of values.</p>

pkg/sql/logictest/testdata/logic_test/builtin_function

@@ -2563,3 +2563,28 @@ query T
 SELECT getdatabaseencoding()
 ----
 UTF8
+
+subtest get_bit
+
+query I
+SELECT get_bit(B'100101110101', 3) UNION SELECT get_bit(B'100101110101', 2)
+----
+1
+0
+
+query error get_bit\(\): GetBitAtIndex: bit index 10 out of valid range \(0..4\)
+SELECT get_bit(B'10110', 10)
+
+subtest set_bit
+
+query T
+SELECT set_bit(B'1101010', 0, 0) UNION SELECT set_bit(B'1101010', 2, 1)
+----
+0101010
+1111010
+
+query error set_bit\(\): SetBitAtIndex: bit index 10 out of valid range \(0..6\)
+SELECT set_bit(B'1101010', 10, 1)
+
+query error set_bit\(\): to_set value must be either 0 or 1 only.
+SELECT set_bit(B'1001010', 0, 2)

pkg/sql/sem/builtins/builtins.go

@@ -321,6 +321,51 @@ var builtins = map[string]builtinDefinition{
 				"Supports encodings 'UTF8' and 'LATIN1'.",
 		}),
 
+	// https://www.postgresql.org/docs/9.0/functions-binarystring.html#FUNCTIONS-BINARYSTRING-OTHER
+	"get_bit": makeBuiltin(tree.FunctionProperties{Category: categoryString},
+		tree.Overload{
+			Types:      tree.ArgTypes{{"bit_string", types.VarBit}, {"index", types.Int}},
+			ReturnType: tree.FixedReturnType(types.Int),
+			Fn: func(_ *tree.EvalContext, args tree.Datums) (tree.Datum, error) {
+				bitString := tree.MustBeDBitArray(args[0])
+				index := tree.MustBeDInt(args[1])
+				bit, err := bitString.GetBitAtIndex(int(index))
+				if err != nil {
+					return nil, err
+				}
+				return tree.NewDInt(tree.DInt(bit)), nil
+			},
+			Info: "Extracts a bit at given index in the bit array",
+		}),
+
+	// https://www.postgresql.org/docs/9.0/functions-binarystring.html#FUNCTIONS-BINARYSTRING-OTHER
+	"set_bit": makeBuiltin(tree.FunctionProperties{Category: categoryString},
+		tree.Overload{
+			Types: tree.ArgTypes{
+				{"bit_string", types.VarBit},
+				{"index", types.Int},
+				{"to_set", types.Int},
+			},
+			ReturnType: tree.FixedReturnType(types.VarBit),
+			Fn: func(_ *tree.EvalContext, args tree.Datums) (tree.Datum, error) {
+				bitString := tree.MustBeDBitArray(args[0])
+				index := tree.MustBeDInt(args[1])
+				toSet := tree.MustBeDInt(args[2])
+
+				// Value of bit can only be set to 1 or 0.
+				if int(toSet) != 0 && int(toSet) != 1 {
+					return nil, pgerror.Newf(pgcode.InvalidParameterValue,
+						"to_set value must be either 0 or 1 only.")
+				}
+				updatedBitString, err := bitString.SetBitAtIndex(int(index), int(toSet))
+				if err != nil {
+					return nil, err
+				}
+				return &tree.DBitArray{BitArray: updatedBitString}, nil
+			},
+			Info: "Updates a bit at given index in the bit array",
+		}),
+
 	"gen_random_uuid": makeBuiltin(
 		tree.FunctionProperties{
 			Category: categoryIDGeneration,