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Diffstat (limited to 'vendor/github.com/google/go-cmp/cmp/internal/diff/diff.go')
| -rw-r--r-- | vendor/github.com/google/go-cmp/cmp/internal/diff/diff.go | 372 |
1 files changed, 372 insertions, 0 deletions
diff --git a/vendor/github.com/google/go-cmp/cmp/internal/diff/diff.go b/vendor/github.com/google/go-cmp/cmp/internal/diff/diff.go new file mode 100644 index 0000000..3d2e426 --- /dev/null +++ b/vendor/github.com/google/go-cmp/cmp/internal/diff/diff.go @@ -0,0 +1,372 @@ +// Copyright 2017, The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE.md file. + +// Package diff implements an algorithm for producing edit-scripts. +// The edit-script is a sequence of operations needed to transform one list +// of symbols into another (or vice-versa). The edits allowed are insertions, +// deletions, and modifications. The summation of all edits is called the +// Levenshtein distance as this problem is well-known in computer science. +// +// This package prioritizes performance over accuracy. That is, the run time +// is more important than obtaining a minimal Levenshtein distance. +package diff + +// EditType represents a single operation within an edit-script. +type EditType uint8 + +const ( + // Identity indicates that a symbol pair is identical in both list X and Y. + Identity EditType = iota + // UniqueX indicates that a symbol only exists in X and not Y. + UniqueX + // UniqueY indicates that a symbol only exists in Y and not X. + UniqueY + // Modified indicates that a symbol pair is a modification of each other. + Modified +) + +// EditScript represents the series of differences between two lists. +type EditScript []EditType + +// String returns a human-readable string representing the edit-script where +// Identity, UniqueX, UniqueY, and Modified are represented by the +// '.', 'X', 'Y', and 'M' characters, respectively. +func (es EditScript) String() string { + b := make([]byte, len(es)) + for i, e := range es { + switch e { + case Identity: + b[i] = '.' + case UniqueX: + b[i] = 'X' + case UniqueY: + b[i] = 'Y' + case Modified: + b[i] = 'M' + default: + panic("invalid edit-type") + } + } + return string(b) +} + +// stats returns a histogram of the number of each type of edit operation. +func (es EditScript) stats() (s struct{ NI, NX, NY, NM int }) { + for _, e := range es { + switch e { + case Identity: + s.NI++ + case UniqueX: + s.NX++ + case UniqueY: + s.NY++ + case Modified: + s.NM++ + default: + panic("invalid edit-type") + } + } + return +} + +// Dist is the Levenshtein distance and is guaranteed to be 0 if and only if +// lists X and Y are equal. +func (es EditScript) Dist() int { return len(es) - es.stats().NI } + +// LenX is the length of the X list. +func (es EditScript) LenX() int { return len(es) - es.stats().NY } + +// LenY is the length of the Y list. +func (es EditScript) LenY() int { return len(es) - es.stats().NX } + +// EqualFunc reports whether the symbols at indexes ix and iy are equal. +// When called by Difference, the index is guaranteed to be within nx and ny. +type EqualFunc func(ix int, iy int) Result + +// Result is the result of comparison. +// NumSame is the number of sub-elements that are equal. +// NumDiff is the number of sub-elements that are not equal. +type Result struct{ NumSame, NumDiff int } + +// BoolResult returns a Result that is either Equal or not Equal. +func BoolResult(b bool) Result { + if b { + return Result{NumSame: 1} // Equal, Similar + } else { + return Result{NumDiff: 2} // Not Equal, not Similar + } +} + +// Equal indicates whether the symbols are equal. Two symbols are equal +// if and only if NumDiff == 0. If Equal, then they are also Similar. +func (r Result) Equal() bool { return r.NumDiff == 0 } + +// Similar indicates whether two symbols are similar and may be represented +// by using the Modified type. As a special case, we consider binary comparisons +// (i.e., those that return Result{1, 0} or Result{0, 1}) to be similar. +// +// The exact ratio of NumSame to NumDiff to determine similarity may change. +func (r Result) Similar() bool { + // Use NumSame+1 to offset NumSame so that binary comparisons are similar. + return r.NumSame+1 >= r.NumDiff +} + +// Difference reports whether two lists of lengths nx and ny are equal +// given the definition of equality provided as f. +// +// 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() +// +// 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 +// favors performance over optimality. The exact output is not guaranteed to +// be stable and may change over time. +func Difference(nx, ny int, f EqualFunc) (es EditScript) { + // This algorithm is based on traversing what is known as an "edit-graph". + // See Figure 1 from "An O(ND) Difference Algorithm and Its Variations" + // by Eugene W. Myers. Since D can be as large as N itself, this is + // effectively O(N^2). Unlike the algorithm from that paper, we are not + // interested in the optimal path, but at least some "decent" path. + // + // For example, let X and Y be lists of symbols: + // X = [A B C A B B A] + // Y = [C B A B A C] + // + // The edit-graph can be drawn as the following: + // A B C A B B A + // ┌─────────────┐ + // C │_|_|\|_|_|_|_│ 0 + // B │_|\|_|_|\|\|_│ 1 + // A │\|_|_|\|_|_|\│ 2 + // B │_|\|_|_|\|\|_│ 3 + // A │\|_|_|\|_|_|\│ 4 + // C │ | |\| | | | │ 5 + // └─────────────┘ 6 + // 0 1 2 3 4 5 6 7 + // + // List X is written along the horizontal axis, while list Y is written + // along the vertical axis. At any point on this grid, if the symbol in + // list X matches the corresponding symbol in list Y, then a '\' is drawn. + // The goal of any minimal edit-script algorithm is to find a path from the + // top-left corner to the bottom-right corner, while traveling through the + // fewest horizontal or vertical edges. + // A horizontal edge is equivalent to inserting a symbol from list X. + // A vertical edge is equivalent to inserting a symbol from list Y. + // 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 + // + // In general: + // • 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)} + fwdFrontier := fwdPath.point // Forward search frontier + revFrontier := revPath.point // Reverse search frontier + + // Search budget bounds the cost of searching for better paths. + // The longest sequence of non-matching symbols that can be tolerated is + // approximately the square-root of the search budget. + searchBudget := 4 * (nx + ny) // O(n) + + // The algorithm below is a greedy, meet-in-the-middle algorithm for + // 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. + // + // 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 + // that two lists commonly differ because elements were added to the front + // or end of the other list. + // + // Running the tests with the "cmp_debug" build tag prints a visualization + // of the algorithm running in real-time. This is educational for + // understanding how the algorithm works. See debug_enable.go. + f = debug.Begin(nx, ny, f, &fwdPath.es, &revPath.es) + for { + // Forward search from the beginning. + if fwdFrontier.X >= revFrontier.X || fwdFrontier.Y >= revFrontier.Y || searchBudget == 0 { + break + } + for stop1, stop2, i := false, false, 0; !(stop1 && stop2) && searchBudget > 0; i++ { + // Search in a diagonal pattern for a match. + z := zigzag(i) + p := point{fwdFrontier.X + z, fwdFrontier.Y - z} + switch { + case p.X >= revPath.X || p.Y < fwdPath.Y: + stop1 = true // Hit top-right corner + case p.Y >= revPath.Y || p.X < fwdPath.X: + stop2 = true // Hit bottom-left corner + case f(p.X, p.Y).Equal(): + // Match found, so connect the path to this point. + fwdPath.connect(p, f) + fwdPath.append(Identity) + // Follow sequence of matches as far as possible. + for fwdPath.X < revPath.X && fwdPath.Y < revPath.Y { + if !f(fwdPath.X, fwdPath.Y).Equal() { + break + } + fwdPath.append(Identity) + } + fwdFrontier = fwdPath.point + stop1, stop2 = true, true + default: + searchBudget-- // Match not found + } + debug.Update() + } + // Advance the frontier towards reverse point. + if revPath.X-fwdFrontier.X >= revPath.Y-fwdFrontier.Y { + fwdFrontier.X++ + } else { + fwdFrontier.Y++ + } + + // Reverse search from the end. + if fwdFrontier.X >= revFrontier.X || fwdFrontier.Y >= revFrontier.Y || searchBudget == 0 { + break + } + for stop1, stop2, i := false, false, 0; !(stop1 && stop2) && searchBudget > 0; i++ { + // Search in a diagonal pattern for a match. + z := zigzag(i) + p := point{revFrontier.X - z, revFrontier.Y + z} + switch { + case fwdPath.X >= p.X || revPath.Y < p.Y: + stop1 = true // Hit bottom-left corner + case fwdPath.Y >= p.Y || revPath.X < p.X: + stop2 = true // Hit top-right corner + case f(p.X-1, p.Y-1).Equal(): + // Match found, so connect the path to this point. + revPath.connect(p, f) + revPath.append(Identity) + // Follow sequence of matches as far as possible. + for fwdPath.X < revPath.X && fwdPath.Y < revPath.Y { + if !f(revPath.X-1, revPath.Y-1).Equal() { + break + } + revPath.append(Identity) + } + revFrontier = revPath.point + stop1, stop2 = true, true + default: + searchBudget-- // Match not found + } + debug.Update() + } + // Advance the frontier towards forward point. + if revFrontier.X-fwdPath.X >= revFrontier.Y-fwdPath.Y { + revFrontier.X-- + } else { + revFrontier.Y-- + } + } + + // Join the forward and reverse paths and then append the reverse path. + fwdPath.connect(revPath.point, f) + for i := len(revPath.es) - 1; i >= 0; i-- { + t := revPath.es[i] + revPath.es = revPath.es[:i] + fwdPath.append(t) + } + debug.Finish() + return fwdPath.es +} + +type path struct { + dir int // +1 if forward, -1 if reverse + point // Leading point of the EditScript path + es EditScript +} + +// connect appends any necessary Identity, Modified, UniqueX, or UniqueY types +// to the edit-script to connect p.point to dst. +func (p *path) connect(dst point, f EqualFunc) { + if p.dir > 0 { + // Connect in forward direction. + for dst.X > p.X && dst.Y > p.Y { + switch r := f(p.X, p.Y); { + case r.Equal(): + p.append(Identity) + case r.Similar(): + p.append(Modified) + case dst.X-p.X >= dst.Y-p.Y: + p.append(UniqueX) + default: + p.append(UniqueY) + } + } + for dst.X > p.X { + p.append(UniqueX) + } + for dst.Y > p.Y { + p.append(UniqueY) + } + } else { + // Connect in reverse direction. + for p.X > dst.X && p.Y > dst.Y { + switch r := f(p.X-1, p.Y-1); { + case r.Equal(): + p.append(Identity) + case r.Similar(): + p.append(Modified) + case p.Y-dst.Y >= p.X-dst.X: + p.append(UniqueY) + default: + p.append(UniqueX) + } + } + for p.X > dst.X { + p.append(UniqueX) + } + for p.Y > dst.Y { + p.append(UniqueY) + } + } +} + +func (p *path) append(t EditType) { + p.es = append(p.es, t) + switch t { + case Identity, Modified: + p.add(p.dir, p.dir) + case UniqueX: + p.add(p.dir, 0) + case UniqueY: + p.add(0, p.dir) + } + debug.Update() +} + +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 { + x = ^x + } + return x >> 1 +} |