diff options
Diffstat (limited to 'lib/diffseq.h')
| -rw-r--r-- | lib/diffseq.h | 144 |
1 files changed, 23 insertions, 121 deletions
diff --git a/lib/diffseq.h b/lib/diffseq.h index 5faaf9a..6be7d83 100644 --- a/lib/diffseq.h +++ b/lib/diffseq.h @@ -1,6 +1,6 @@ /* Analyze differences between two vectors. - Copyright (C) 1988-1989, 1992-1995, 2001-2004, 2006-2013 Free Software + Copyright (C) 1988-1989, 1992-1995, 2001-2004, 2006-2016 Free Software Foundation, Inc. This program is free software: you can redistribute it and/or modify @@ -26,26 +26,23 @@ distance" in Wikipedia. The basic algorithm is described in: - "An O(ND) Difference Algorithm and its Variations", Eugene Myers, - Algorithmica Vol. 1 No. 2, 1986, pp. 251-266; - see especially section 4.2, which describes the variation used below. + "An O(ND) Difference Algorithm and its Variations", Eugene W. Myers, + Algorithmica Vol. 1, 1986, pp. 251-266, + <http://dx.doi.org/10.1007/BF01840446>. + See especially section 4.2, which describes the variation used below. The basic algorithm was independently discovered as described in: - "Algorithms for Approximate String Matching", E. Ukkonen, - Information and Control Vol. 64, 1985, pp. 100-118. - - Unless the 'find_minimal' flag is set, this code uses the TOO_EXPENSIVE - heuristic, by Paul Eggert, to limit the cost to O(N**1.5 log N) - at the price of producing suboptimal output for large inputs with - many differences. */ + "Algorithms for Approximate String Matching", Esko Ukkonen, + Information and Control Vol. 64, 1985, pp. 100-118, + <http://dx.doi.org/10.1016/S0019-9958(85)80046-2>. */ /* Before including this file, you need to define: ELEMENT The element type of the vectors being compared. EQUAL A two-argument macro that tests two elements for equality. OFFSET A signed integer type sufficient to hold the - difference between two indices. Usually - something like ssize_t. + difference between two indices. Usually + something like ptrdiff_t. EXTRA_CONTEXT_FIELDS Declarations of fields for 'struct context'. NOTE_DELETE(ctxt, xoff) Record the removal of the object xvec[xoff]. NOTE_INSERT(ctxt, yoff) Record the insertion of the object yvec[yoff]. @@ -79,7 +76,7 @@ /* Use this to suppress gcc's "...may be used before initialized" warnings. Beware: The Code argument must not contain commas. */ #ifndef IF_LINT -# ifdef lint +# if defined GCC_LINT || defined lint # define IF_LINT(Code) Code # else # define IF_LINT(Code) /* empty */ @@ -88,7 +85,7 @@ /* As above, but when Code must contain one comma. */ #ifndef IF_LINT2 -# ifdef lint +# if defined GCC_LINT || defined lint # define IF_LINT2(Code1, Code2) Code1, Code2 # else # define IF_LINT2(Code1, Code2) /* empty */ @@ -120,15 +117,12 @@ struct context OFFSET *bdiag; #ifdef USE_HEURISTIC - /* This corresponds to the diff -H flag. With this heuristic, for - vectors with a constant small density of changes, the algorithm is - linear in the vectors size. */ + /* This corresponds to the diff --speed-large-files flag. With this + heuristic, for vectors with a constant small density of changes, + the algorithm is linear in the vector size. */ bool heuristic; #endif - /* Edit scripts longer than this are too expensive to compute. */ - OFFSET too_expensive; - /* Snakes bigger than this are considered "big". */ #define SNAKE_LIMIT 20 }; @@ -138,12 +132,6 @@ struct partition /* Midpoints of this partition. */ OFFSET xmid; OFFSET ymid; - - /* True if low half will be analyzed minimally. */ - bool lo_minimal; - - /* Likewise for high half. */ - bool hi_minimal; }; @@ -155,17 +143,10 @@ struct partition When the two searches meet, we have found the midpoint of the shortest edit sequence. - If FIND_MINIMAL is true, find the minimal edit script regardless of - expense. Otherwise, if the search is too expensive, use heuristics to - stop the search and report a suboptimal answer. - - Set PART->(xmid,ymid) to the midpoint (XMID,YMID). The diagonal number + Set *PART to the midpoint (XMID,YMID). The diagonal number XMID - YMID equals the number of inserted elements minus the number of deleted elements (counting only elements before the midpoint). - Set PART->lo_minimal to true iff the minimal edit script for the - left half of the partition is known; similarly for PART->hi_minimal. - This function assumes that the first elements of the specified portions of the two vectors do not match, and likewise that the last elements do not match. The caller must trim matching elements from the beginning and end @@ -175,7 +156,7 @@ struct partition suboptimal diff output. It cannot cause incorrect diff output. */ static void -diag (OFFSET xoff, OFFSET xlim, OFFSET yoff, OFFSET ylim, bool find_minimal, +diag (OFFSET xoff, OFFSET xlim, OFFSET yoff, OFFSET ylim, struct partition *part, struct context *ctxt) { OFFSET *const fd = ctxt->fdiag; /* Give the compiler a chance. */ @@ -235,7 +216,6 @@ diag (OFFSET xoff, OFFSET xlim, OFFSET yoff, OFFSET ylim, bool find_minimal, { part->xmid = x; part->ymid = y; - part->lo_minimal = part->hi_minimal = true; return; } } @@ -268,14 +248,10 @@ diag (OFFSET xoff, OFFSET xlim, OFFSET yoff, OFFSET ylim, bool find_minimal, { part->xmid = x; part->ymid = y; - part->lo_minimal = part->hi_minimal = true; return; } } - if (find_minimal) - continue; - #ifdef USE_HEURISTIC /* Heuristic: check occasionally for a diagonal that has made lots of progress compared with the edit distance. If we have any @@ -319,11 +295,7 @@ diag (OFFSET xoff, OFFSET xlim, OFFSET yoff, OFFSET ylim, bool find_minimal, } } if (best > 0) - { - part->lo_minimal = true; - part->hi_minimal = false; - return; - } + return; } { @@ -358,77 +330,10 @@ diag (OFFSET xoff, OFFSET xlim, OFFSET yoff, OFFSET ylim, bool find_minimal, } } if (best > 0) - { - part->lo_minimal = false; - part->hi_minimal = true; - return; - } + return; } } #endif /* USE_HEURISTIC */ - - /* Heuristic: if we've gone well beyond the call of duty, give up - and report halfway between our best results so far. */ - if (c >= ctxt->too_expensive) - { - OFFSET fxybest; - OFFSET fxbest IF_LINT (= 0); - OFFSET bxybest; - OFFSET bxbest IF_LINT (= 0); - - /* Find forward diagonal that maximizes X + Y. */ - fxybest = -1; - for (d = fmax; d >= fmin; d -= 2) - { - OFFSET x = MIN (fd[d], xlim); - OFFSET y = x - d; - if (ylim < y) - { - x = ylim + d; - y = ylim; - } - if (fxybest < x + y) - { - fxybest = x + y; - fxbest = x; - } - } - - /* Find backward diagonal that minimizes X + Y. */ - bxybest = OFFSET_MAX; - for (d = bmax; d >= bmin; d -= 2) - { - OFFSET x = MAX (xoff, bd[d]); - OFFSET y = x - d; - if (y < yoff) - { - x = yoff + d; - y = yoff; - } - if (x + y < bxybest) - { - bxybest = x + y; - bxbest = x; - } - } - - /* Use the better of the two diagonals. */ - if ((xlim + ylim) - bxybest < fxybest - (xoff + yoff)) - { - part->xmid = fxbest; - part->ymid = fxybest - fxbest; - part->lo_minimal = true; - part->hi_minimal = false; - } - else - { - part->xmid = bxbest; - part->ymid = bxybest - bxbest; - part->lo_minimal = false; - part->hi_minimal = true; - } - return; - } } #undef XREF_YREF_EQUAL } @@ -442,9 +347,6 @@ diag (OFFSET xoff, OFFSET xlim, OFFSET yoff, OFFSET ylim, bool find_minimal, Note that XLIM, YLIM are exclusive bounds. All indices into the vectors are origin-0. - If FIND_MINIMAL, find a minimal difference no matter how - expensive it is. - The results are recorded by invoking NOTE_DELETE and NOTE_INSERT. Return false if terminated normally, or true if terminated through early @@ -452,7 +354,7 @@ diag (OFFSET xoff, OFFSET xlim, OFFSET yoff, OFFSET ylim, bool find_minimal, static bool compareseq (OFFSET xoff, OFFSET xlim, OFFSET yoff, OFFSET ylim, - bool find_minimal, struct context *ctxt) + struct context *ctxt) { #ifdef ELEMENT ELEMENT const *xv = ctxt->xvec; /* Help the compiler. */ @@ -498,12 +400,12 @@ compareseq (OFFSET xoff, OFFSET xlim, OFFSET yoff, OFFSET ylim, struct partition part IF_LINT2 (= { .xmid = 0, .ymid = 0 }); /* Find a point of correspondence in the middle of the vectors. */ - diag (xoff, xlim, yoff, ylim, find_minimal, &part, ctxt); + diag (xoff, xlim, yoff, ylim, &part, ctxt); /* Use the partitions to split this problem into subproblems. */ - if (compareseq (xoff, part.xmid, yoff, part.ymid, part.lo_minimal, ctxt)) + if (compareseq (xoff, part.xmid, yoff, part.ymid, ctxt)) return true; - if (compareseq (part.xmid, xlim, part.ymid, ylim, part.hi_minimal, ctxt)) + if (compareseq (part.xmid, xlim, part.ymid, ylim, ctxt)) return true; } |