snuyanzin commented on code in PR #29004:
URL: https://github.com/apache/flink/pull/29004#discussion_r3837741170


##########
flink-table/flink-table-runtime/src/main/java/org/apache/flink/table/runtime/functions/SqlFunctionUtils.java:
##########
@@ -345,29 +331,39 @@ public static String rpad(String base, int len, String 
pad) {
             return "";
         }
 
-        char[] data = new char[len];
-        char[] baseChars = base.toCharArray();
-        char[] padChars = pad.toCharArray();
+        int baseEnd = endOfCodePoints(base, len);
+        int padChars = padLength(pad, len - base.codePointCount(0, baseEnd));
+        char[] data = new char[baseEnd + padChars];
+
+        base.getChars(0, baseEnd, data, 0);
+        writePad(data, baseEnd, pad, padChars);
 
-        int pos = 0;
+        return new String(data);
+    }
 
-        // copy the base
-        while (pos < base.length() && pos < len) {
-            data[pos] = baseChars[pos];
-            pos += 1;
+    /** Index just past the first count code points of str, or its end if str 
holds fewer. */
+    private static int endOfCodePoints(String str, int count) {
+        int index = 0;
+        for (int i = 0; i < count && index < str.length(); i++) {
+            index += Character.charCount(str.codePointAt(index));
         }
+        return index;
+    }
 
-        // copy the padding
-        while (pos < len) {
-            int i = 0;
-            while (i < pad.length() && i < len - pos) {
-                data[pos + i] = padChars[i];
-                i += 1;
-            }
+    /** Number of chars taken by count code points of pad repeated cyclically. 
*/
+    private static int padLength(String pad, int count) {
+        int cycle = pad.codePointCount(0, pad.length());
+        return (count / cycle) * pad.length() + endOfCodePoints(pad, count % 
cycle);
+    }
+
+    /** Writes chars characters into data at pos, repeating pad cyclically. */
+    private static void writePad(char[] data, int pos, String pad, int chars) {
+        int end = pos + chars;
+        while (end - pos >= pad.length()) {

Review Comment:
   why do we need extra calculations here?
   extract `pad.length()` into a var



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