Support for generation number v5: backward compatible corrected date

README.md

@@ -159,6 +159,23 @@ the minimum felineX(A) and minimum felineY(B) among all explored commits
 A and B. That is, the pair (minX, minY) is below our entire explored set.
 This can be a disadvantage for these algorithms.
 
+**V5: Corrected Commit Date with Strictly Monotonic Offset.**
+For a commit C, let its _offset commit date_ (denoted by odate(C))
+be a commit date plus some offset, i.e. odate(C) = date(C) + offset(C),
+such that:
+
+1. Offset commit date is greater than the maximum of the commit date
+   of C and the offset commit dates of its parents.
+
+     If odate(A) < odate(B), then A cannot reach B.
+
+2. Offset of a commit is one more than the maximum offset of a parent,
+   or more
+
+     If offset(A) < offset(B), then A cannot reach B.
+
+This is backward-compatible version of V3: Corrected Commit Date.
+
 ### Comparing Reachability Index Versions Viability
 
 Before considering how well these indexes perform during our algorithm
@@ -189,12 +206,18 @@ Git clients.
 | Maximum Generation Number | Yes         | No         | No     |
 | Corrected Commit Date     | No          | Yes        | Yes    |
 | FELINE index              | Yes         | No         | No     |
+| Offset Commit Date *NEW*  | Yes         | Yes        | Yes    |
 
 _Note:_ The corrected commit date uses the generation number column
 to store an offset of "how much do I need to add to my commit date
 to get my corrected commit date?" The values stored in that column
 are then not backwards-compatible.
 
+_Note:_ The corrected commit date with strictly monotonic offset also
+uses the generation number column to store the date offset, but the
+offset alone can be used as generation number (as reachability index)
+itself.
+
 _Note:_ The FELINE index requires storing two values instead of just
 one. One of these values could be stored in the generation number
 column and the other in an optional chunk, hence it could be backwards

create-graphs.sh

@@ -5,10 +5,10 @@ do
 	(
 		echo $repo
 		cd $repo
-		../git/git commit-graph write --reachable --version=0	
+		../git/git commit-graph write --reachable --version=0
 		cp .git/objects/info/commit-graph .git/objects/info/commit-graph.0
-	
-		for v in 1 2 3 4
+
+		for v in 1 2 3 4 5
 		do
 			cp .git/objects/info/commit-graph.0 .git/objects/info/commit-graph
 			../git/git commit-graph write --reachable --version=$v

merge-base-tests.sh

@@ -19,7 +19,7 @@ do
 		| sed "s/:/ /g" \
 		| grep -oE '[^ ]+$')"
 
-	for v in 0 1 2 3 4 
+	for v in 0 1 2 3 4 5
 	do
 		cp .git/objects/info/commit-graph.$v .git/objects/info/commit-graph
 

topo-compare-tests.sh

@@ -18,7 +18,7 @@ do
 		| sed "s/:/ /g" \
 		| grep -oE '[^ ]+$')"
 
-	for v in 0 1 2 3 4 
+	for v in 0 1 2 3 4 5
 	do
 		cp .git/objects/info/commit-graph.$v .git/objects/info/commit-graph
 
@@ -42,7 +42,7 @@ do
 		| sed "s/:/ /g" \
 		| grep -oE '[^ ]+$')"
 
-	for v in 0 1 2 3 4 
+	for v in 0 1 2 3 4 5
 	do
 		cp .git/objects/info/commit-graph.$v .git/objects/info/commit-graph
 

topo-order-tests.sh

@@ -10,7 +10,7 @@ do
 	for n in 100 1000 10000
 	do
 		cp .git/objects/info/commit-graph.0 .git/objects/info/commit-graph
-	
+
 		LOGFILE=$TESTDIR/log-$repo-$n-$v.txt
 		rm -f $LOGFILE
 
@@ -20,7 +20,7 @@ do
 			| sed "s/:/ /g" \
 			| grep -oE '[^ ]+$')"
 
-		for v in 0 1 2 3 4 
+		for v in 0 1 2 3 4 5
 		do
 			cp .git/objects/info/commit-graph.$v .git/objects/info/commit-graph