char refactor

Author: James Cor

sql/expression/function/char.go

@@ -85,18 +85,26 @@ func (c *Char) CollationCoercibility(ctx *sql.Context) (collation sql.CollationI
 	return sql.Collation_binary, 5
 }
 
-// char converts num into a byte array
-// This function is essentially converting the number to base 256
-func char(num uint32) []byte {
-	if num == 0 {
-		return []byte{}
+// encodeUint32 converts uint32 `num` into a []byte using the fewest number of bytes in big endian (no leading 0s)
+func encodeUint32(num uint32) []byte {
+	res := []byte{
+		byte(num >> 24),
+		byte(num >> 16),
+		byte(num >> 8),
+		byte(num),
 	}
-	return append(char(num>>8), byte(num&255))
+	var i int
+	for i = 0; i < 3; i++ {
+		if res[i] != 0 {
+			break
+		}
+	}
+	return res[i:]
 }
 
 // Eval implements the sql.Expression interface
 func (c *Char) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
-	res := []byte{}
+	var res []byte
 	for _, arg := range c.args {
 		if arg == nil {
 			continue
@@ -114,11 +122,9 @@ func (c *Char) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
 		v, _, err := types.Uint32.Convert(ctx, val)
 		if err != nil {
 			ctx.Warn(1292, "Truncated incorrect INTEGER value: '%v'", val)
-			res = append(res, 0)
-			continue
 		}
 
-		res = append(res, char(v.(uint32))...)
+		res = append(res, encodeUint32(v.(uint32))...)
 	}
 
 	result, _, err := c.Type().Convert(ctx, res)

sql/types/conversion.go

@@ -767,7 +767,7 @@ func TypeAwareConversion(ctx *sql.Context, val interface{}, originalType sql.Typ
 // cleanly and the type is automatically coerced (i.e. string and numeric types), then a warning is logged and the
 // value is truncated to the Zero value for type |t|. If the value does not convert and the type is not automatically
 // coerced, then return an error.
-// TODO: This logic should be in types.Convert()
+// TODO: Should truncate to number prefix instead of Zero.
 func ConvertOrTruncate(ctx *sql.Context, i interface{}, t sql.Type) (interface{}, error) {
 	converted, _, err := t.Convert(ctx, i)
 	if err == nil {