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Extract surrogate fixup from StrBuilder.reverse() to reduce structural depth #1764

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Extract surrogate fixup from StrBuilder.reverse() to reduce structural depth #1764

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24 changes: 13 additions & 11 deletions src/main/java/org/apache/commons/lang3/text/StrBuilder.java
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Original file line number Diff line number Diff line change
Expand Up @@ -2756,7 +2756,6 @@ public StrBuilder reverse() {
if (size == 0) {
return this;
}

final int half = size / 2;
final char[] buf = buffer;
boolean hasSurrogates = false;
Expand All @@ -2768,20 +2767,23 @@ public StrBuilder reverse() {
hasSurrogates |= Character.isSurrogate(left) || Character.isSurrogate(right);
}
if (hasSurrogates) {
// The plain swap leaves each surrogate pair in low-high order; restore the high-low order so a
// reversed supplementary code point stays a valid pair, matching StringBuilder#reverse().
for (int i = 0; i < size - 1; i++) {
if (Character.isLowSurrogate(buf[i]) && Character.isHighSurrogate(buf[i + 1])) {
final char low = buf[i];
buf[i] = buf[i + 1];
buf[i + 1] = low;
i++;
}
}
restoreSurrogatePairs(buf, size);
}
return this;
}

/** Restore high-low order of surrogate pairs that were inverted during reversal. */
private void restoreSurrogatePairs(final char[] buf, final int size) {
for (int i = 0; i < size - 1; i++) {
if (Character.isLowSurrogate(buf[i]) && Character.isHighSurrogate(buf[i + 1])) {
final char low = buf[i];
buf[i] = buf[i + 1];
buf[i + 1] = low;
i++;
}
}
}

/**
* Extracts the rightmost characters from the string builder without
* throwing an exception.
Expand Down