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8370822: Improve performance for MemorySegment::fill #28031

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8370822: Improve performance for MemorySegment::fill #28031

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3 changes: 2 additions & 1 deletion src/java.base/share/classes/jdk/internal/foreign/SegmentBulkOperations.java
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Original file line number Diff line number Diff line change
Expand Up @@ -50,6 +50,7 @@ private SegmentBulkOperations() {}

private static final ScopedMemoryAccess SCOPED_MEMORY_ACCESS = ScopedMemoryAccess.getScopedMemoryAccess();
private static final long LONG_MASK = ~7L; // The last three bits are zero
private static final long BYTE_REPLICATOR = 0x0101010101010101L;

// All the threshold values below MUST be a power of two and should preferably be
// greater or equal to 2^3.
Expand All @@ -68,7 +69,7 @@ public static MemorySegment fill(AbstractMemorySegmentImpl dst, byte value) {

// Handle smaller segments directly without transitioning to native code
final long u = Byte.toUnsignedLong(value);
final long longValue = u << 56 | u << 48 | u << 40 | u << 32 | u << 24 | u << 16 | u << 8 | u;
final long longValue = BYTE_REPLICATOR * u;

int offset = 0;
// 0...0X...X000
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