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Diffstat (limited to 'plumbing/format/packfile/diff.go')
| -rw-r--r-- | plumbing/format/packfile/diff.go | 397 |
1 files changed, 397 insertions, 0 deletions
diff --git a/plumbing/format/packfile/diff.go b/plumbing/format/packfile/diff.go new file mode 100644 index 0000000..ff34329 --- /dev/null +++ b/plumbing/format/packfile/diff.go @@ -0,0 +1,397 @@ +package packfile + +/* + +Copyright (c) 2013, Patrick Mezard +All rights reserved. + +Redistribution and use in source and binary forms, with or without +modification, are permitted provided that the following conditions are +met: + + Redistributions of source code must retain the above copyright +notice, this list of conditions and the following disclaimer. + Redistributions in binary form must reproduce the above copyright +notice, this list of conditions and the following disclaimer in the +documentation and/or other materials provided with the distribution. + The names of its contributors may not be used to endorse or promote +products derived from this software without specific prior written +permission. + +THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS +IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED +TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A +PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT +HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, +SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED +TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR +PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF +LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING +NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS +SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. + +*/ + +// Code based on https://github.com/pmezard/go-difflib +// Removed unnecessary code for this use case and changed string inputs to byte + +type match struct { + A int + B int + Size int +} + +type opCode struct { + Tag byte + I1 int + I2 int + J1 int + J2 int +} + +// SequenceMatcher compares sequence of bytes. The basic +// algorithm predates, and is a little fancier than, an algorithm +// published in the late 1980's by Ratcliff and Obershelp under the +// hyperbolic name "gestalt pattern matching". The basic idea is to find +// the longest contiguous matching subsequence that contains no "junk" +// elements (R-O doesn't address junk). The same idea is then applied +// recursively to the pieces of the sequences to the left and to the right +// of the matching subsequence. This does not yield minimal edit +// sequences, but does tend to yield matches that "look right" to people. +// +// SequenceMatcher tries to compute a "human-friendly diff" between two +// sequences. Unlike e.g. UNIX(tm) diff, the fundamental notion is the +// longest *contiguous* & junk-free matching subsequence. That's what +// catches peoples' eyes. The Windows(tm) windiff has another interesting +// notion, pairing up elements that appear uniquely in each sequence. +// That, and the method here, appear to yield more intuitive difference +// reports than does diff. This method appears to be the least vulnerable +// to synching up on blocks of "junk lines", though (like blank lines in +// ordinary text files, or maybe "<P>" lines in HTML files). That may be +// because this is the only method of the 3 that has a *concept* of +// "junk" <wink>. +// +// Timing: Basic R-O is cubic time worst case and quadratic time expected +// case. SequenceMatcher is quadratic time for the worst case and has +// expected-case behavior dependent in a complicated way on how many +// elements the sequences have in common; best case time is linear. +type sequenceMatcher struct { + a []byte + b []byte + b2j map[byte][]int + IsJunk func(byte) bool + autoJunk bool + bJunk map[byte]struct{} + matchingBlocks []match + fullBCount map[byte]int + bPopular map[byte]struct{} + opCodes []opCode +} + +func newMatcher(a, b []byte) *sequenceMatcher { + m := sequenceMatcher{autoJunk: true} + m.SetSeqs(a, b) + return &m +} + +// Set two sequences to be compared. +func (m *sequenceMatcher) SetSeqs(a, b []byte) { + m.SetSeq1(a) + m.SetSeq2(b) +} + +// Set the first sequence to be compared. The second sequence to be compared is +// not changed. +// +// SequenceMatcher computes and caches detailed information about the second +// sequence, so if you want to compare one sequence S against many sequences, +// use .SetSeq2(s) once and call .SetSeq1(x) repeatedly for each of the other +// sequences. +// +// See also SetSeqs() and SetSeq2(). +func (m *sequenceMatcher) SetSeq1(a []byte) { + if &a == &m.a { + return + } + m.a = a + m.matchingBlocks = nil + m.opCodes = nil +} + +// Set the second sequence to be compared. The first sequence to be compared is +// not changed. +func (m *sequenceMatcher) SetSeq2(b []byte) { + if &b == &m.b { + return + } + m.b = b + m.matchingBlocks = nil + m.opCodes = nil + m.fullBCount = nil + m.chainB() +} + +func (m *sequenceMatcher) chainB() { + // Populate line -> index mapping + b2j := map[byte][]int{} + for i, s := range m.b { + indices := b2j[s] + indices = append(indices, i) + b2j[s] = indices + } + + // Purge junk elements + m.bJunk = map[byte]struct{}{} + if m.IsJunk != nil { + junk := m.bJunk + for s := range b2j { + if m.IsJunk(s) { + junk[s] = struct{}{} + } + } + for s := range junk { + delete(b2j, s) + } + } + + // Purge remaining popular elements + popular := map[byte]struct{}{} + n := len(m.b) + if m.autoJunk && n >= 200 { + ntest := n/100 + 1 + for s, indices := range b2j { + if len(indices) > ntest { + popular[s] = struct{}{} + } + } + for s := range popular { + delete(b2j, s) + } + } + m.bPopular = popular + m.b2j = b2j +} + +func (m *sequenceMatcher) isBJunk(s byte) bool { + _, ok := m.bJunk[s] + return ok +} + +// Find longest matching block in a[alo:ahi] and b[blo:bhi]. +// +// If IsJunk is not defined: +// +// Return (i,j,k) such that a[i:i+k] is equal to b[j:j+k], where +// alo <= i <= i+k <= ahi +// blo <= j <= j+k <= bhi +// and for all (i',j',k') meeting those conditions, +// k >= k' +// i <= i' +// and if i == i', j <= j' +// +// In other words, of all maximal matching blocks, return one that +// starts earliest in a, and of all those maximal matching blocks that +// start earliest in a, return the one that starts earliest in b. +// +// If IsJunk is defined, first the longest matching block is +// determined as above, but with the additional restriction that no +// junk element appears in the block. Then that block is extended as +// far as possible by matching (only) junk elements on both sides. So +// the resulting block never matches on junk except as identical junk +// happens to be adjacent to an "interesting" match. +// +// If no blocks match, return (alo, blo, 0). +func (m *sequenceMatcher) findLongestMatch(alo, ahi, blo, bhi int) match { + // CAUTION: stripping common prefix or suffix would be incorrect. + // E.g., + // ab + // acab + // Longest matching block is "ab", but if common prefix is + // stripped, it's "a" (tied with "b"). UNIX(tm) diff does so + // strip, so ends up claiming that ab is changed to acab by + // inserting "ca" in the middle. That's minimal but unintuitive: + // "it's obvious" that someone inserted "ac" at the front. + // Windiff ends up at the same place as diff, but by pairing up + // the unique 'b's and then matching the first two 'a's. + besti, bestj, bestsize := alo, blo, 0 + + // find longest junk-free match + // during an iteration of the loop, j2len[j] = length of longest + // junk-free match ending with a[i-1] and b[j] + j2len := map[int]int{} + for i := alo; i != ahi; i++ { + // look at all instances of a[i] in b; note that because + // b2j has no junk keys, the loop is skipped if a[i] is junk + newj2len := map[int]int{} + for _, j := range m.b2j[m.a[i]] { + // a[i] matches b[j] + if j < blo { + continue + } + if j >= bhi { + break + } + k := j2len[j-1] + 1 + newj2len[j] = k + if k > bestsize { + besti, bestj, bestsize = i-k+1, j-k+1, k + } + } + j2len = newj2len + } + + // Extend the best by non-junk elements on each end. In particular, + // "popular" non-junk elements aren't in b2j, which greatly speeds + // the inner loop above, but also means "the best" match so far + // doesn't contain any junk *or* popular non-junk elements. + for besti > alo && bestj > blo && !m.isBJunk(m.b[bestj-1]) && + m.a[besti-1] == m.b[bestj-1] { + besti, bestj, bestsize = besti-1, bestj-1, bestsize+1 + } + for besti+bestsize < ahi && bestj+bestsize < bhi && + !m.isBJunk(m.b[bestj+bestsize]) && + m.a[besti+bestsize] == m.b[bestj+bestsize] { + bestsize += 1 + } + + // Now that we have a wholly interesting match (albeit possibly + // empty!), we may as well suck up the matching junk on each + // side of it too. Can't think of a good reason not to, and it + // saves post-processing the (possibly considerable) expense of + // figuring out what to do with it. In the case of an empty + // interesting match, this is clearly the right thing to do, + // because no other kind of match is possible in the regions. + for besti > alo && bestj > blo && m.isBJunk(m.b[bestj-1]) && + m.a[besti-1] == m.b[bestj-1] { + besti, bestj, bestsize = besti-1, bestj-1, bestsize+1 + } + for besti+bestsize < ahi && bestj+bestsize < bhi && + m.isBJunk(m.b[bestj+bestsize]) && + m.a[besti+bestsize] == m.b[bestj+bestsize] { + bestsize += 1 + } + + return match{A: besti, B: bestj, Size: bestsize} +} + +// Return list of triples describing matching subsequences. +// +// Each triple is of the form (i, j, n), and means that +// a[i:i+n] == b[j:j+n]. The triples are monotonically increasing in +// i and in j. It's also guaranteed that if (i, j, n) and (i', j', n') are +// adjacent triples in the list, and the second is not the last triple in the +// list, then i+n != i' or j+n != j'. IOW, adjacent triples never describe +// adjacent equal blocks. +// +// The last triple is a dummy, (len(a), len(b), 0), and is the only +// triple with n==0. +func (m *sequenceMatcher) GetMatchingBlocks() []match { + if m.matchingBlocks != nil { + return m.matchingBlocks + } + + var matchBlocks func(alo, ahi, blo, bhi int, matched []match) []match + matchBlocks = func(alo, ahi, blo, bhi int, matched []match) []match { + match := m.findLongestMatch(alo, ahi, blo, bhi) + i, j, k := match.A, match.B, match.Size + if match.Size > 0 { + if alo < i && blo < j { + matched = matchBlocks(alo, i, blo, j, matched) + } + matched = append(matched, match) + if i+k < ahi && j+k < bhi { + matched = matchBlocks(i+k, ahi, j+k, bhi, matched) + } + } + return matched + } + matched := matchBlocks(0, len(m.a), 0, len(m.b), nil) + + // It's possible that we have adjacent equal blocks in the + // matching_blocks list now. + nonAdjacent := []match{} + i1, j1, k1 := 0, 0, 0 + for _, b := range matched { + // Is this block adjacent to i1, j1, k1? + i2, j2, k2 := b.A, b.B, b.Size + if i1+k1 == i2 && j1+k1 == j2 { + // Yes, so collapse them -- this just increases the length of + // the first block by the length of the second, and the first + // block so lengthened remains the block to compare against. + k1 += k2 + } else { + // Not adjacent. Remember the first block (k1==0 means it's + // the dummy we started with), and make the second block the + // new block to compare against. + if k1 > 0 { + nonAdjacent = append(nonAdjacent, match{i1, j1, k1}) + } + i1, j1, k1 = i2, j2, k2 + } + } + if k1 > 0 { + nonAdjacent = append(nonAdjacent, match{i1, j1, k1}) + } + + nonAdjacent = append(nonAdjacent, match{len(m.a), len(m.b), 0}) + m.matchingBlocks = nonAdjacent + return m.matchingBlocks +} + +const ( + tagReplace = 'r' + tagDelete = 'd' + tagInsert = 'i' + tagEqual = 'e' +) + +// Return list of 5-tuples describing how to turn a into b. +// +// Each tuple is of the form (tag, i1, i2, j1, j2). The first tuple +// has i1 == j1 == 0, and remaining tuples have i1 == the i2 from the +// tuple preceding it, and likewise for j1 == the previous j2. +// +// The tags are characters, with these meanings: +// +// 'r' (replace): a[i1:i2] should be replaced by b[j1:j2] +// +// 'd' (delete): a[i1:i2] should be deleted, j1==j2 in this case. +// +// 'i' (insert): b[j1:j2] should be inserted at a[i1:i1], i1==i2 in this case. +// +// 'e' (equal): a[i1:i2] == b[j1:j2] +func (m *sequenceMatcher) GetOpCodes() []opCode { + if m.opCodes != nil { + return m.opCodes + } + i, j := 0, 0 + matching := m.GetMatchingBlocks() + opCodes := make([]opCode, 0, len(matching)) + for _, m := range matching { + // invariant: we've pumped out correct diffs to change + // a[:i] into b[:j], and the next matching block is + // a[ai:ai+size] == b[bj:bj+size]. So we need to pump + // out a diff to change a[i:ai] into b[j:bj], pump out + // the matching block, and move (i,j) beyond the match + ai, bj, size := m.A, m.B, m.Size + tag := byte(0) + if i < ai && j < bj { + tag = tagReplace + } else if i < ai { + tag = tagDelete + } else if j < bj { + tag = tagInsert + } + if tag > 0 { + opCodes = append(opCodes, opCode{tag, i, ai, j, bj}) + } + i, j = ai+size, bj+size + // the list of matching blocks is terminated by a + // sentinel with size 0 + if size > 0 { + opCodes = append(opCodes, opCode{tagEqual, ai, i, bj, j}) + } + } + m.opCodes = opCodes + return m.opCodes +} |