expression: implement vectorized evaluation for 'builtinCastRealAsStr…

…ingSig' (#12533)

expression/builtin_cast_vec.go

@@ -156,11 +156,53 @@ func (b *builtinCastTimeAsJSONSig) vecEvalJSON(input *chunk.Chunk, result *chunk
 }
 
 func (b *builtinCastRealAsStringSig) vectorized() bool {
-	return false
+	return true
 }
 
 func (b *builtinCastRealAsStringSig) vecEvalString(input *chunk.Chunk, result *chunk.Column) error {
-	return errors.Errorf("not implemented")
+	n := input.NumRows()
+	buf, err := b.bufAllocator.get(types.ETReal, n)
+	if err != nil {
+		return err
+	}
+	defer b.bufAllocator.put(buf)
+	if err := b.args[0].VecEvalReal(b.ctx, input, buf); err != nil {
+		return err
+	}
+
+	bits := 64
+	if b.args[0].GetType().Tp == mysql.TypeFloat {
+		// b.args[0].EvalReal() casts the value from float32 to float64, for example:
+		// float32(208.867) is cast to float64(208.86700439)
+		// If we strconv.FormatFloat the value with 64bits, the result is incorrect!
+		bits = 32
+	}
+
+	var isNull bool
+	var res string
+	f64s := buf.Float64s()
+	result.ReserveString(n)
+	sc := b.ctx.GetSessionVars().StmtCtx
+	for i, v := range f64s {
+		if buf.IsNull(i) {
+			result.AppendNull()
+			continue
+		}
+		res, err = types.ProduceStrWithSpecifiedTp(strconv.FormatFloat(v, 'f', -1, bits), b.tp, sc, false)
+		if err != nil {
+			return err
+		}
+		res, isNull, err = padZeroForBinaryType(res, b.tp, b.ctx)
+		if err != nil {
+			return err
+		}
+		if isNull {
+			result.AppendNull()
+			continue
+		}
+		result.AppendString(res)
+	}
+	return nil
 }
 
 func (b *builtinCastDecimalAsStringSig) vectorized() bool {

expression/builtin_cast_vec_test.go

@@ -37,6 +37,7 @@ var vecBuiltinCastCases = map[string][]vecExprBenchCase{
 		},
 		{retEvalType: types.ETString, childrenTypes: []types.EvalType{types.ETInt}},
 		{retEvalType: types.ETDecimal, childrenTypes: []types.EvalType{types.ETDatetime}},
+		{retEvalType: types.ETString, childrenTypes: []types.EvalType{types.ETReal}},
 		{retEvalType: types.ETString, childrenTypes: []types.EvalType{types.ETJson}},
 		{retEvalType: types.ETString, childrenTypes: []types.EvalType{types.ETDecimal}},
 	},