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Allow ObjectToPack subclasses to use up to 4 bits of flags 

Some instances may benefit from having access to memory efficient
storage for some small values, like single flag bits.  Give up a
portion of our delta depth field to make 4 bits available to any
subclass that wants it.

This still gives us room for delta chains of 1,048,576 objects,
and that is just insane.  Unpacking 1 million objects to get to
something is longer than most users are willing to wait for data
from Git.

Change-Id: If17ea598dc0ddbde63d69a6fcec0668106569125
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
This commit is contained in:
Shawn O. Pearce 2010-08-02 12:26:01 -07:00
parent f048af3fd1
commit fe18e52195
1 changed files with 69 additions and 3 deletions
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72
org.eclipse.jgit/src/org/eclipse/jgit/storage/pack/ObjectToPack.java
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@ -68,9 +68,15 @@ public class ObjectToPack extends PackedObjectInfo {
private static final int TYPE_SHIFT = 5;
private static final int DELTA_SHIFT = 8;
private static final int EXT_SHIFT = 8;
private static final int NON_DELTA_MASK = 0xff;
private static final int EXT_MASK = 0xf;
private static final int DELTA_SHIFT = 12;
private static final int NON_EXT_MASK = ~(EXT_MASK << EXT_SHIFT);
private static final int NON_DELTA_MASK = 0xfff;
/** Other object being packed that this will delta against. */
private ObjectId deltaBase;
@ -84,8 +90,9 @@ public class ObjectToPack extends PackedObjectInfo {
* <li>1 bit: edgeObject</li>
* <li>1 bit: unused</li>
* <li>3 bits: type</li>
* <li>4 bits: subclass flags (if any)</li>
* <li>--</li>
* <li>24 bits: deltaDepth</li>
* <li>20 bits: deltaDepth</li>
* </ul>
*/
private int flags;
@ -254,6 +261,65 @@ void setEdge() {
flags |= EDGE;
}
/** @return the extended flags on this object, in the range [0x0, 0xf]. */
protected int getExtendedFlags() {
return (flags >>> EXT_SHIFT) & EXT_MASK;
}
/**
* Determine if a particular extended flag bit has been set.
*
* This implementation may be faster than calling
* {@link #getExtendedFlags()} and testing the result.
*
* @param flag
* the flag mask to test, must be between 0x0 and 0xf.
* @return true if any of the bits matching the mask are non-zero.
*/
protected boolean isExtendedFlag(int flag) {
return (flags & (flag << EXT_SHIFT)) != 0;
}
/**
* Set an extended flag bit.
*
* This implementation is more efficient than getting the extended flags,
* adding the bit, and setting them all back.
*
* @param flag
* the bits to set, must be between 0x0 and 0xf.
*/
protected void setExtendedFlag(int flag) {
flags |= (flag & EXT_MASK) << EXT_SHIFT;
}
/**
* Clear an extended flag bit.
*
* This implementation is more efficient than getting the extended flags,
* removing the bit, and setting them all back.
*
* @param flag
* the bits to clear, must be between 0x0 and 0xf.
*/
protected void clearExtendedFlag(int flag) {
flags &= ~((flag & EXT_MASK) << EXT_SHIFT);
}
/**
* Set the extended flags used by the subclass.
*
* Subclass implementations may store up to 4 bits of information inside of
* the internal flags field already used by the base ObjectToPack instance.
*
* @param extFlags
* additional flag bits to store in the flags field. Due to space
* constraints only values [0x0, 0xf] are permitted.
*/
protected void setExtendedFlags(int extFlags) {
flags = ((extFlags & EXT_MASK) << EXT_SHIFT) | (flags & NON_EXT_MASK);
}
int getFormat() {
if (isReuseAsIs()) {
if (isDeltaRepresentation())