SEPURI-SAI-KRISHNA commented on code in PR #29004:
URL: https://github.com/apache/flink/pull/29004#discussion_r3838007255
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flink-table/flink-table-runtime/src/main/java/org/apache/flink/table/runtime/functions/SqlFunctionUtils.java:
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@@ -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()) {
+ pad.getChars(0, pad.length(), data, pos);
Review Comment:
So i tried it: `pad.repeat(n)` then one `getChars` allocates the padding as
a String first, so it measures slower, 309 vs 142 ns at 1000 chars.
`String.repeat` is itself this loop: JDK 17 does `System.arraycopy` with
`copied <<= 1` for a multi-char string, and `Arrays.fill` when the string is 1
char.
The second half looks worth taking: `Arrays.fill` for `padLen == 1` is
faster up to ~1000 chars (4 vs 18 ns at 8 chars, 11 vs 39 at 128). Add that and
keep the doubling for longer pads?
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