diff options
Diffstat (limited to 'cmp/internal/diff/diff.go')
| -rw-r--r-- | cmp/internal/diff/diff.go | 44 |
1 files changed, 24 insertions, 20 deletions
diff --git a/cmp/internal/diff/diff.go b/cmp/internal/diff/diff.go index bc196b1..a248e54 100644 --- a/cmp/internal/diff/diff.go +++ b/cmp/internal/diff/diff.go @@ -127,9 +127,9 @@ var randBool = rand.New(rand.NewSource(time.Now().Unix())).Intn(2) == 0 // This function returns an edit-script, which is a sequence of operations // needed to convert one list into the other. The following invariants for // the edit-script are maintained: -// • eq == (es.Dist()==0) -// • nx == es.LenX() -// • ny == es.LenY() +// - eq == (es.Dist()==0) +// - nx == es.LenX() +// - ny == es.LenY() // // This algorithm is not guaranteed to be an optimal solution (i.e., one that // produces an edit-script with a minimal Levenshtein distance). This algorithm @@ -169,12 +169,13 @@ func Difference(nx, ny int, f EqualFunc) (es EditScript) { // A diagonal edge is equivalent to a matching symbol between both X and Y. // Invariants: - // • 0 ≤ fwdPath.X ≤ (fwdFrontier.X, revFrontier.X) ≤ revPath.X ≤ nx - // • 0 ≤ fwdPath.Y ≤ (fwdFrontier.Y, revFrontier.Y) ≤ revPath.Y ≤ ny + // - 0 ≤ fwdPath.X ≤ (fwdFrontier.X, revFrontier.X) ≤ revPath.X ≤ nx + // - 0 ≤ fwdPath.Y ≤ (fwdFrontier.Y, revFrontier.Y) ≤ revPath.Y ≤ ny // // In general: - // • fwdFrontier.X < revFrontier.X - // • fwdFrontier.Y < revFrontier.Y + // - fwdFrontier.X < revFrontier.X + // - fwdFrontier.Y < revFrontier.Y + // // Unless, it is time for the algorithm to terminate. fwdPath := path{+1, point{0, 0}, make(EditScript, 0, (nx+ny)/2)} revPath := path{-1, point{nx, ny}, make(EditScript, 0)} @@ -195,19 +196,21 @@ func Difference(nx, ny int, f EqualFunc) (es EditScript) { // computing sub-optimal edit-scripts between two lists. // // The algorithm is approximately as follows: - // • Searching for differences switches back-and-forth between - // a search that starts at the beginning (the top-left corner), and - // a search that starts at the end (the bottom-right corner). The goal of - // the search is connect with the search from the opposite corner. - // • As we search, we build a path in a greedy manner, where the first - // match seen is added to the path (this is sub-optimal, but provides a - // decent result in practice). When matches are found, we try the next pair - // of symbols in the lists and follow all matches as far as possible. - // • When searching for matches, we search along a diagonal going through - // through the "frontier" point. If no matches are found, we advance the - // frontier towards the opposite corner. - // • This algorithm terminates when either the X coordinates or the - // Y coordinates of the forward and reverse frontier points ever intersect. + // - Searching for differences switches back-and-forth between + // a search that starts at the beginning (the top-left corner), and + // a search that starts at the end (the bottom-right corner). + // The goal of the search is connect with the search + // from the opposite corner. + // - As we search, we build a path in a greedy manner, + // where the first match seen is added to the path (this is sub-optimal, + // but provides a decent result in practice). When matches are found, + // we try the next pair of symbols in the lists and follow all matches + // as far as possible. + // - When searching for matches, we search along a diagonal going through + // through the "frontier" point. If no matches are found, + // we advance the frontier towards the opposite corner. + // - This algorithm terminates when either the X coordinates or the + // Y coordinates of the forward and reverse frontier points ever intersect. // This algorithm is correct even if searching only in the forward direction // or in the reverse direction. We do both because it is commonly observed @@ -389,6 +392,7 @@ type point struct{ X, Y int } func (p *point) add(dx, dy int) { p.X += dx; p.Y += dy } // zigzag maps a consecutive sequence of integers to a zig-zag sequence. +// // [0 1 2 3 4 5 ...] => [0 -1 +1 -2 +2 ...] func zigzag(x int) int { if x&1 != 0 { |