diff.nim: massive code cleanups

1 files changed, 90 insertions, 166 deletions

diff --git a/lib/std/diff.nim b/lib/std/diff.nim
index 940b5888d..bffce2803 100644
--- a/lib/std/diff.nim
+++ b/lib/std/diff.nim
@@ -1,145 +1,90 @@
-
-## This Class implements the Difference Algorithm published in
-## "An O(ND) Difference Algorithm and its Variations" by Eugene Myers
-## Algorithmica Vol. 1 No. 2, 1986, p 251.
-##
-## There are many C, Java, Lisp implementations public available but they all seem to come
-## from the same source (diffutils) that is under the (unfree) GNU public License
-## and cannot be reused as a sourcecode for a commercial application.
-## There are very old C implementations that use other (worse) algorithms.
-## Microsoft also published sourcecode of a diff-tool (windiff) that uses some tree data.
-## Also, a direct transfer from a C source to C# is not easy because there is a lot of pointer
-## arithmetic in the typical C solutions and i need a managed solution.
-## These are the reasons why I implemented the original published algorithm from the scratch and
-## make it avaliable without the GNU license limitations.
-## I do not need a high performance diff tool because it is used only sometimes.
-## I will do some performace tweaking when needed.
-##
-## The algorithm itself is comparing 2 arrays of numbers so when comparing 2 text documents
-## each line is converted into a (hash) number. See diffText().
-##
-## Some chages to the original algorithm:
-## The original algorithm was described using a recursive approach and comparing zero indexed arrays.
-## Extracting sub-arrays and rejoining them is very performance and memory intensive so the same
-## (readonly) data arrays are passed arround together with their lower and upper bounds.
-## This circumstance makes the lcs and sms functions more complicate.
-## I added some code to the lcs function to get a fast response on sub-arrays that are identical,
-## completely deleted or inserted.
-##
-## The result from a comparisation is stored in 2 arrays that flag for modified (deleted or inserted)
-## lines in the 2 data arrays. These bits are then analysed to produce a array of Item objects.
-##
-## Further possible optimizations:
-## (first rule: don't do it; second: don't do it yet)
-## The arrays dataA and dataB are passed as parameters, but are never changed after the creation
-## so they can be members of the class to avoid the paramter overhead.
-## In sms is a lot of boundary arithmetic in the for-D and for-k loops that can be done by increment
-## and decrement of local variables.
-## The downVector and upVector arrays are alywas created and destroyed each time the sms gets called.
-## It is possible to reuse tehm when transfering them to members of the class.
-## See TODO: hints.
-##
-## diff.cs: A port of the algorythm to C#
-## Copyright (c) by Matthias Hertel, http://www.mathertel.de
-## This work is licensed under a BSD style license. See http://www.mathertel.de/License.aspx
-##
-## Changes:
-## 2002.09.20 There was a "hang" in some situations.
-## Now I undestand a little bit more of the sms algorithm.
-## There have been overlapping boxes; that where analyzed partial differently.
-## One return-point is enough.
-## A assertion was added in createDiffs when in debug-mode, that counts the number of equal (no modified) lines in both arrays.
-## They must be identical.
-##
-## 2003.02.07 Out of bounds error in the Up/Down vector arrays in some situations.
-## The two vetors are now accessed using different offsets that are adjusted using the start k-Line.
-## A test case is added.
-##
-## 2006.03.05 Some documentation and a direct Diff entry point.
-##
-## 2006.03.08 Refactored the API to static methods on the Diff class to make usage simpler.
-## 2006.03.10 using the standard Debug class for self-test now.
-##            compile with: csc /target:exe /out:diffTest.exe /d:DEBUG /d:TRACE /d:SELFTEST Diff.cs
-## 2007.01.06 license agreement changed to a BSD style license.
-## 2007.06.03 added the optimize method.
-## 2007.09.23 upVector and downVector optimization by Jan Stoklasa ().
-## 2008.05.31 Adjusted the testing code that failed because of the optimize method (not a bug in the diff algorithm).
-## 2008.10.08 Fixing a test case and adding a new test case.
-## 2018.12.07 Port to Nim.
+#
+#
+#            Nim's Runtime Library
+#        (c) Copyright 2018 Nim contributors
+#
+#    See the file "copying.txt", included in this
+#    distribution, for details about the copyright.
+#
+
+## This module implements an algorithm to compute the
+## `diff`:idx: between two sequences of lines.
+
+# code owner: Arne Döring
+#
+# This is based on C# code written by Matthias Hertel, http://www.mathertel.de
+#
+# This Class implements the Difference Algorithm published in
+# "An O(ND) Difference Algorithm and its Variations" by Eugene Myers
+# Algorithmica Vol. 1 No. 2, 1986, p 251.
 
 import tables, strutils
 
 type
-  Item* = object
+  Item* = object    ## An Item in the list of differences.
     startA*: int    ## Start Line number in Data A.
     startB*: int    ## Start Line number in Data B.
     deletedA*: int  ## Number of changes in Data A.
     insertedB*: int ## Number of changes in Data B.
 
-  DiffData = object
-    ## Data on one input file being compared.
-    len: int ## Number of elements (lines).
+  DiffData = object ## Data on one input file being compared.
     data: seq[int] ## Buffer of numbers that will be compared.
     modified: seq[bool] ## Array of booleans that flag for modified
-                        ## data.  This is the result of the diff.
+                        ## data. This is the result of the diff.
                         ## This means deletedA in the first Data or
                         ## inserted in the second Data.
 
-  SMSRD = object
-    x,y: int
+  Smsrd = object
+    x, y: int
+
+# template to avoid a seq copy. Required until ``sink`` parameters are ready.
+template newDiffData(initData: seq[int]; L: int): DiffData =
+  DiffData(
+    data: initData,
+    modified: newSeq[bool](L + 2)
+  )
 
-proc newDiffData(initData: seq[int]): DiffData =
-  ## Initialize the Diff-Data buffer.
-  result.len = initData.len
-  result.data = initData
-  result.modified = newSeq[bool](result.len + 2)
+proc len(d: DiffData): int {.inline.} = d.data.len
 
-proc diffCodes(aText: string; h: var Table[string,int]): seq[int] =
+proc diffCodes(aText: string; h: var Table[string, int]): DiffData =
   ## This function converts all textlines of the text into unique numbers for every unique textline
   ## so further work can work only with simple numbers.
   ## ``aText`` the input text
   ## ``h`` This extern initialized hashtable is used for storing all ever used textlines.
   ## ``trimSpace`` ignore leading and trailing space characters
   ## Returns a array of integers.
-
-  # get all codes of the text
   var lastUsedCode = h.len
-  var codes = newSeq[int]()
+  result.data = newSeq[int]()
   for s in aText.splitLines:
     if h.contains s:
-      codes.add h[s]
+      result.data.add h[s]
     else:
       inc lastUsedCode
       h[s] = lastUsedCode
-      codes.add lastUsedCode
+      result.data.add lastUsedCode
+  result.modified = newSeq[bool](result.data.len + 2)
 
-  return codes
-
-proc optimize(data: var DiffData): void =
+proc optimize(data: var DiffData) =
   ## If a sequence of modified lines starts with a line that contains the same content
   ## as the line that appends the changes, the difference sequence is modified so that the
   ## appended line and not the starting line is marked as modified.
   ## This leads to more readable diff sequences when comparing text files.
-  ## ``data`` A Diff data buffer containing the identified changes.
-
-  var startPos, endPos: int
-  startPos = 0
-
+  var startPos = 0
   while startPos < data.len:
-    while (startPos < data.len) and (data.modified[startPos] == false):
+    while startPos < data.len and not data.modified[startPos]:
       inc startPos
-    endPos = startPos
-    while (endPos < data.len) and (data.modified[endPos] == true):
+    var endPos = startPos
+    while endPos < data.len and data.modified[endPos]:
       inc endPos
 
-    if (endPos < data.len) and (data.data[startPos] == data.data[endPos]):
+    if endPos < data.len and data.data[startPos] == data.data[endPos]:
       data.modified[startPos] = false
       data.modified[endPos] = true
     else:
       startPos = endPos
 
 proc sms(dataA: var DiffData; lowerA, upperA: int; dataB: DiffData; lowerB, upperB: int;
-  downVector, upVector: var openArray[int]): SMSRD =
+         downVector, upVector: var openArray[int]): Smsrd =
   ## This is the algorithm to find the Shortest Middle Snake (sms).
   ## ``dataA`` sequence A
   ## ``lowerA`` lower bound of the actual range in dataA
@@ -151,10 +96,10 @@ proc sms(dataA: var DiffData; lowerA, upperA: int; dataB: DiffData; lowerB, uppe
   ## ``upVector`` a vector for the (u,v) to (N,M) search. Passed as a parameter for speed reasons.
   ## Returns a MiddleSnakeData record containing x,y and u,v.
 
-  let max: int = dataA.len + dataB.len + 1
+  let max = dataA.len + dataB.len + 1
 
-  let downK = lowerA - lowerB; # the k-line to start the forward search
-  let upK = upperA - upperB; # the k-line to start the reverse search
+  let downK = lowerA - lowerB # the k-line to start the forward search
+  let upK = upperA - upperB # the k-line to start the reverse search
 
   let delta = (upperA - lowerA) - (upperB - lowerB)
   let oddDelta = (delta and 1) != 0
@@ -166,75 +111,64 @@ proc sms(dataA: var DiffData; lowerA, upperA: int; dataB: DiffData; lowerB, uppe
 
   let maxD = ((upperA - lowerA + upperB - lowerB) div 2) + 1
 
-  # Debug.Write(2, "sms", String.Format("Search the box: A[{0}-{1}] to B[{2}-{3}]", lowerA, upperA, lowerB, upperB))
-
-  # init vectors
   downVector[downOffset + downK + 1] = lowerA
   upVector[upOffset + upK - 1] = upperA
 
   for D in 0 .. maxD:
-
     # Extend the forward path.
-
     for k in countUp(downK - D, downK + D, 2):
-      # Debug.Write(0, "sms", "extend forward path " + k.ToString())
-
       # find the only or better starting point
-      var x, y: int
+      var x: int
       if k == downK - D:
-        x = downVector[downOffset + k + 1]; # down
+        x = downVector[downOffset + k + 1] # down
       else:
-        x = downVector[downOffset + k - 1] + 1; # a step to the right
-        if (k < downK + D) and (downVector[downOffset + k + 1] >= x):
-          x = downVector[downOffset + k + 1]; # down
+        x = downVector[downOffset + k - 1] + 1 # a step to the right
+        if k < downK + D and downVector[downOffset + k + 1] >= x:
+          x = downVector[downOffset + k + 1] # down
 
-      y = x - k
+      var y = x - k
 
       # find the end of the furthest reaching forward D-path in diagonal k.
-      while (x < upperA) and (y < upperB) and (dataA.data[x] == dataB.data[y]):
+      while x < upperA and y < upperB and dataA.data[x] == dataB.data[y]:
         inc x
         inc y
 
       downVector[downOffset + k] = x
 
       # overlap ?
-      if oddDelta and (upK - D < k) and (k < upK + D):
+      if oddDelta and upK - D < k and k < upK + D:
         if upVector[upOffset + k] <= downVector[downOffset + k]:
-          result.x = downVector[downOffset + k]
-          result.y = downVector[downOffset + k] - k
-          return
+          return Smsrd(x: downVector[downOffset + k],
+                       y: downVector[downOffset + k] - k)
 
     # Extend the reverse path.
     for k in countUp(upK - D, upK + D, 2):
-      # Debug.Write(0, "sms", "extend reverse path " + k.ToString())
-
       # find the only or better starting point
-      var x, y: int
+      var x: int
       if k == upK + D:
-        x = upVector[upOffset + k - 1]; # up
+        x = upVector[upOffset + k - 1] # up
       else:
-        x = upVector[upOffset + k + 1] - 1; # left
-        if (k > upK - D) and (upVector[upOffset + k - 1] < x):
-          x = upVector[upOffset + k - 1]; # up
-      # if
-      y = x - k
+        x = upVector[upOffset + k + 1] - 1 # left
+        if k > upK - D and upVector[upOffset + k - 1] < x:
+          x = upVector[upOffset + k - 1] # up
 
-      while (x > lowerA) and (y > lowerB) and (dataA.data[x - 1] == dataB.data[y - 1]):
+      var y = x - k
+      while x > lowerA and y > lowerB and dataA.data[x - 1] == dataB.data[y - 1]:
         dec x
         dec y
 
       upVector[upOffset + k] = x
 
       # overlap ?
-      if (not oddDelta) and (downK - D <= k) and (k <= downK + D):
+      if not oddDelta and downK-D <= k and k <= downK+D:
         if upVector[upOffset + k] <= downVector[downOffset + k]:
-          result.x = downVector[downOffset + k]
-          result.y = downVector[downOffset + k] - k
-          return
+          return Smsrd(x: downVector[downOffset + k],
+                       y: downVector[downOffset + k] - k)
 
   assert false, "the algorithm should never come here."
 
-proc lcs(dataA: var DiffData; lowerA, upperA: int; dataB: var DiffData; lowerB, upperB: int; downVector, upVector: var openArray[int]): void =
+proc lcs(dataA: var DiffData; lowerA, upperA: int; dataB: var DiffData; lowerB, upperB: int;
+         downVector, upVector: var openArray[int]) =
   ## This is the divide-and-conquer implementation of the longes common-subsequence (lcs)
   ## algorithm.
   ## The published algorithm passes recursively parts of the A and B sequences.
@@ -247,14 +181,13 @@ proc lcs(dataA: var DiffData; lowerA, upperA: int; dataB: var DiffData; lowerB,
   ## ``upperB`` upper bound of the actual range in dataB (exclusive)
   ## ``downVector`` a vector for the (0,0) to (x,y) search. Passed as a parameter for speed reasons.
   ## ``upVector`` a vector for the (u,v) to (N,M) search. Passed as a parameter for speed reasons.
-  # make mutable copy
+
+  # make mutable copy:
   var lowerA = lowerA
   var lowerB = lowerB
   var upperA = upperA
   var upperB = upperB
 
-  # Debug.Write(2, "lcs", String.Format("Analyse the box: A[{0}-{1}] to B[{2}-{3}]", lowerA, upperA, lowerB, upperB))
-
   # Fast walkthrough equal lines at the start
   while lowerA < upperA and lowerB < upperB and dataA.data[lowerA] == dataB.data[lowerB]:
     inc lowerA
@@ -286,20 +219,16 @@ proc lcs(dataA: var DiffData; lowerA, upperA: int; dataB: var DiffData; lowerB,
     lcs(dataA, lowerA, smsrd.x, dataB, lowerB, smsrd.y, downVector, upVector)
     lcs(dataA, smsrd.x, upperA, dataB, smsrd.y, upperB, downVector, upVector)  # 2002.09.20: no need for 2 points
 
-# lcs()
-
 proc createDiffs(dataA, dataB: DiffData): seq[Item] =
   ## Scan the tables of which lines are inserted and deleted,
   ## producing an edit script in forward order.
-
-  var startA: int
-  var startB: int
-  var lineA: int
-  var lineB: int
-
+  var startA = 0
+  var startB = 0
+  var lineA = 0
+  var lineB = 0
   while lineA < dataA.len or lineB < dataB.len:
-    if (lineA < dataA.len) and (not dataA.modified[lineA]) and
-       (lineB < dataB.len) and (not dataB.modified[lineB]):
+    if lineA < dataA.len and not dataA.modified[lineA] and
+       lineB < dataB.len and not dataB.modified[lineB]:
       # equal lines
       inc lineA
       inc lineB
@@ -309,21 +238,16 @@ proc createDiffs(dataA, dataB: DiffData): seq[Item] =
       startB = lineB
 
       while lineA < dataA.len and (lineB >= dataB.len or dataA.modified[lineA]):
-        # while (lineA < dataA.len and dataA.modified[lineA])
         inc lineA
 
       while lineB < dataB.len and (lineA >= dataA.len or dataB.modified[lineB]):
-        # while (lineB < dataB.len and dataB.modified[lineB])
         inc lineB
 
       if (startA < lineA) or (startB < lineB):
-        # store a new difference-item
-        var aItem: Item
-        aItem.startA = startA
-        aItem.startB = startB
-        aItem.deletedA = lineA - startA
-        aItem.insertedB = lineB - startB
-        result.add aItem
+        result.add Item(startA: startA,
+                        startB: startB,
+                        deletedA: lineA - startA,
+                        insertedB: lineB - startB)
 
 
 proc diffInt*(arrayA, arrayB: openArray[int]): seq[Item] =
@@ -333,10 +257,10 @@ proc diffInt*(arrayA, arrayB: openArray[int]): seq[Item] =
   ## Returns a array of Items that describe the differences.
 
   # The A-Version of the data (original data) to be compared.
-  var dataA = newDiffData(@arrayA)
+  var dataA = newDiffData(@arrayA, arrayA.len)
 
   # The B-Version of the data (modified data) to be compared.
-  var dataB = newDiffData(@arrayB)
+  var dataB = newDiffData(@arrayB, arrayB.len)
 
   let max = dataA.len + dataB.len + 1
   ## vector for the (0,0) to (x,y) search
@@ -345,9 +269,9 @@ proc diffInt*(arrayA, arrayB: openArray[int]): seq[Item] =
   var upVector = newSeq[int](2 * max + 2)
 
   lcs(dataA, 0, dataA.len, dataB, 0, dataB.len, downVector, upVector)
-  return createDiffs(dataA, dataB)
+  result = createDiffs(dataA, dataB)
 
-proc diffText*(textA,textB: string): seq[Item] =
+proc diffText*(textA, textB: string): seq[Item] =
   ## Find the difference in 2 text documents, comparing by textlines.
   ## The algorithm itself is comparing 2 arrays of numbers so when comparing 2 text documents
   ## each line is converted into a (hash) number. This hash-value is computed by storing all
@@ -361,12 +285,12 @@ proc diffText*(textA,textB: string): seq[Item] =
   ## Returns a seq of Items that describe the differences.
 
   # prepare the input-text and convert to comparable numbers.
-  var h = initTable[string,int]()  # TextA.len + TextB.len  <- probably wrong initial size
+  var h = initTable[string, int]()  # TextA.len + TextB.len  <- probably wrong initial size
   # The A-Version of the data (original data) to be compared.
-  var dataA = newDiffData(diffCodes(textA, h))
+  var dataA = diffCodes(textA, h)
 
   # The B-Version of the data (modified data) to be compared.
-  var dataB = newDiffData(diffCodes(textB, h))
+  var dataB = diffCodes(textB, h)
 
   h.clear # free up hashtable memory (maybe)
 
@@ -380,7 +304,7 @@ proc diffText*(textA,textB: string): seq[Item] =
 
   optimize(dataA)
   optimize(dataB)
-  return createDiffs(dataA, dataB)
+  result = createDiffs(dataA, dataB)
 
 when isMainModule:
 
@@ -390,7 +314,7 @@ when isMainModule:
         $it.deletedA & "." & $it.insertedB & "." & $it.startA & "." & $it.startB & "*"
       )
 
-  proc main(): void =
+  proc main() =
     var a, b: string
 
     stdout.writeLine("Diff Self Test...")