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perf: unroll first probe in ClassNameFilter.contains() #67

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perf: unroll first probe in ClassNameFilter.contains() #67

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31 changes: 20 additions & 11 deletions utils/src/main/java/datadog/instrument/utils/ClassNameFilter.java
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Original file line number Diff line number Diff line change
Expand Up @@ -64,19 +64,28 @@ public boolean contains(CharSequence className) {
final long[] members = this.members;
final int slotMask = this.slotMask;

// try to find matching slot, rehashing after each attempt
for (int i = 1, h = hash; true; i++, h = rehash(h)) {
long codeAndHash = members[slotMask & h];
if (codeAndHash != 0) {
// check hash first as it's cheap, then check class-code
if ((int) codeAndHash == hash) {
return checkClassCode(className, (int) (codeAndHash >>> 32));
} else if (i < MAX_HASH_ATTEMPTS) {
continue; // rehash and try again
}
}
// first probe without rehash (most common path)
long codeAndHash = members[slotMask & hash];
if (codeAndHash == 0) {
return false;
}
if ((int) codeAndHash == hash) {
return checkClassCode(className, (int) (codeAndHash >>> 32));
}

// subsequent probes with rehash (collision path)
int h = hash;
for (int i = 2; i <= MAX_HASH_ATTEMPTS; i++) {
h = Integer.reverseBytes(h * 0x9e3775cd) * 0x9e3775cd;
codeAndHash = members[slotMask & h];
if (codeAndHash == 0) {
return false;
}
if ((int) codeAndHash == hash) {
return checkClassCode(className, (int) (codeAndHash >>> 32));
}
}
return false;
}

/**
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