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perf: use ISO_8859_1 for ASCII fast path in ClassFile.utf() #66

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Merged
gh-worker-dd-mergequeue-cf854d merged 1 commit into from
Apr 9, 2026
Merged

perf: use ISO_8859_1 for ASCII fast path in ClassFile.utf() #66

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7 changes: 5 additions & 2 deletions class-match/src/main/java/datadog/instrument/classmatch/ClassFile.java
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@

package datadog.instrument.classmatch;

import static java.nio.charset.StandardCharsets.ISO_8859_1;
import static java.nio.charset.StandardCharsets.US_ASCII;

import java.util.Arrays;
Expand Down Expand Up @@ -353,8 +354,10 @@ private static String utf(byte[] bytecode, int utfOffset) {
}

if (chars == null) {
// fast-path for ASCII-only, avoids intermediate char array
return new String(bytecode, utfStart, utfLen, US_ASCII);
// fast-path for ASCII-only: use ISO_8859_1 because on Java 9+ the JVM
// can adopt the byte array directly as the compact string encoding,
// avoiding a byte-by-byte transcoding step that US_ASCII requires
return new String(bytecode, utfStart, utfLen, ISO_8859_1);
}

int charLen = 0;
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