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Avoid extra byte[] allocation and double-copy when constructing MachineState

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catbref 2020-04-14 17:16:12 +01:00
parent 6dc717f3de
commit 582921aa54
1 changed files with 13 additions and 11 deletions
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24
Java/src/main/java/org/ciyam/at/MachineState.java
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@ -522,8 +522,8 @@ public class MachineState {
} }
/** For restoring a previously serialized machine state */ /** For restoring a previously serialized machine state */
public static MachineState fromBytes(API api, AtLoggerFactory loggerFactory, byte[] bytes, byte[] codeBytes) { public static MachineState fromBytes(API api, AtLoggerFactory loggerFactory, byte[] stateBytes, byte[] codeBytes) {
ByteBuffer byteBuffer = ByteBuffer.wrap(bytes); ByteBuffer byteBuffer = ByteBuffer.wrap(stateBytes);
byte[] headerBytes = new byte[HEADER_LENGTH]; byte[] headerBytes = new byte[HEADER_LENGTH];
byteBuffer.get(headerBytes); byteBuffer.get(headerBytes);
@ -533,27 +533,29 @@ public class MachineState {
if (codeBytes.length != state.codeByteBuffer.capacity()) if (codeBytes.length != state.codeByteBuffer.capacity())
throw new IllegalStateException("Passed codeBytes does not match length in header"); throw new IllegalStateException("Passed codeBytes does not match length in header");
// Pull in code bytes
System.arraycopy(codeBytes, 0, state.codeByteBuffer.array(), 0, codeBytes.length); System.arraycopy(codeBytes, 0, state.codeByteBuffer.array(), 0, codeBytes.length);
byte[] dataBytes = new byte[state.dataByteBuffer.capacity()]; // Pull in data bytes
byteBuffer.get(dataBytes); int dataBytesLength = state.dataByteBuffer.capacity();
System.arraycopy(dataBytes, 0, state.dataByteBuffer.array(), 0, dataBytes.length); System.arraycopy(stateBytes, byteBuffer.position(), state.dataByteBuffer.array(), 0, dataBytesLength);
byteBuffer.position(byteBuffer.position() + dataBytesLength);
// Pull in call stack
int callStackLength = byteBuffer.getInt(); int callStackLength = byteBuffer.getInt();
byte[] callStackBytes = new byte[callStackLength];
byteBuffer.get(callStackBytes);
// Restore call stack pointer, and useful for copy below // Restore call stack pointer, and useful for copy below
state.callStackByteBuffer.position(state.callStackByteBuffer.limit() - callStackLength); state.callStackByteBuffer.position(state.callStackByteBuffer.limit() - callStackLength);
// Call stack grows downwards so copy to end // Call stack grows downwards so copy to end
System.arraycopy(callStackBytes, 0, state.callStackByteBuffer.array(), state.callStackByteBuffer.position(), callStackLength); System.arraycopy(stateBytes, byteBuffer.position(), state.callStackByteBuffer.array(), state.callStackByteBuffer.position(), callStackLength);
byteBuffer.position(byteBuffer.position() + callStackLength);
// Pull in user stack
int userStackLength = byteBuffer.getInt(); int userStackLength = byteBuffer.getInt();
byte[] userStackBytes = new byte[userStackLength];
byteBuffer.get(userStackBytes);
// Restore user stack pointer, and useful for copy below // Restore user stack pointer, and useful for copy below
state.userStackByteBuffer.position(state.userStackByteBuffer.limit() - userStackLength); state.userStackByteBuffer.position(state.userStackByteBuffer.limit() - userStackLength);
// User stack grows downwards so copy to end // User stack grows downwards so copy to end
System.arraycopy(userStackBytes, 0, state.userStackByteBuffer.array(), state.userStackByteBuffer.position(), userStackLength); System.arraycopy(stateBytes, byteBuffer.position(), state.userStackByteBuffer.array(), state.userStackByteBuffer.position(), userStackLength);
byteBuffer.position(byteBuffer.position() + userStackLength);
// Actual state // Actual state
state.programCounter = byteBuffer.getInt(); state.programCounter = byteBuffer.getInt();