#define NOTE_INSERT(ctxt, yoff) ctxt->yvec_edit_count++
/* We don't need USE_HEURISTIC, since it is unlikely in typical uses of
fstrcmp(). */
-
-/* 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.
- 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].
- USE_HEURISTIC (Optional) Define if you want to support the
- heuristic for large vectors. */
-
-/* Maximum value of type OFFSET. */
-#define OFFSET_MAX \
- ((((OFFSET)1 << (sizeof (OFFSET) * CHAR_BIT - 2)) - 1) * 2 + 1)
-
-/* Use this to suppress gcc's `...may be used before initialized' warnings. */
-#ifndef IF_LINT
-# ifdef lint
-# define IF_LINT(Code) Code
-# else
-# define IF_LINT(Code) /* empty */
-# endif
-#endif
-
-/*
- * Context of comparison operation.
- */
-struct context
-{
- /* Vectors being compared. */
- const ELEMENT *xvec;
- const ELEMENT *yvec;
-
- /* The number of elements inserted or deleted. */
- int xvec_edit_count;
- int yvec_edit_count;
-
- /* Vector, indexed by diagonal, containing 1 + the X coordinate of the point
- furthest along the given diagonal in the forward search of the edit
- matrix. */
- OFFSET *fdiag;
-
- /* Vector, indexed by diagonal, containing the X coordinate of the point
- furthest along the given diagonal in the backward search of the edit
- matrix. */
- 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. */
- 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
-};
-
-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;
-};
-
-
-/* Find the midpoint of the shortest edit script for a specified portion
- of the two vectors.
-
- Scan from the beginnings of the vectors, and simultaneously from the ends,
- doing a breadth-first search through the space of edit-sequence.
- 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
- 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
- of the portions it is going to specify.
-
- If we return the "wrong" partitions, the worst this can do is cause
- suboptimal diff output. It cannot cause incorrect diff output. */
-
-static void
-diag (OFFSET xoff, OFFSET xlim, OFFSET yoff, OFFSET ylim, bool find_minimal,
- struct partition *part, struct context *ctxt)
-{
- OFFSET *const fd = ctxt->fdiag; /* Give the compiler a chance. */
- OFFSET *const bd = ctxt->bdiag; /* Additional help for the compiler. */
- const ELEMENT *const xv = ctxt->xvec; /* Still more help for the compiler. */
- const ELEMENT *const yv = ctxt->yvec; /* And more and more . . . */
- const OFFSET dmin = xoff - ylim; /* Minimum valid diagonal. */
- const OFFSET dmax = xlim - yoff; /* Maximum valid diagonal. */
- const OFFSET fmid = xoff - yoff; /* Center diagonal of top-down search. */
- const OFFSET bmid = xlim - ylim; /* Center diagonal of bottom-up search. */
- OFFSET fmin = fmid;
- OFFSET fmax = fmid; /* Limits of top-down search. */
- OFFSET bmin = bmid;
- OFFSET bmax = bmid; /* Limits of bottom-up search. */
- OFFSET c; /* Cost. */
- bool odd = (fmid - bmid) & 1; /* True if southeast corner is on an odd
- diagonal with respect to the northwest. */
-
- fd[fmid] = xoff;
- bd[bmid] = xlim;
-
- for (c = 1;; ++c)
- {
- OFFSET d; /* Active diagonal. */
- bool big_snake = false;
-
- /* Extend the top-down search by an edit step in each diagonal. */
- if (fmin > dmin)
- fd[--fmin - 1] = -1;
- else
- ++fmin;
- if (fmax < dmax)
- fd[++fmax + 1] = -1;
- else
- --fmax;
- for (d = fmax; d >= fmin; d -= 2)
- {
- OFFSET x;
- OFFSET y;
- OFFSET oldx;
- OFFSET tlo = fd[d - 1];
- OFFSET thi = fd[d + 1];
-
- if (tlo >= thi)
- x = tlo + 1;
- else
- x = thi;
- oldx = x;
- y = x - d;
- while (x < xlim && y < ylim && xv[x] == yv[y])
- {
- ++x;
- ++y;
- }
- if (x - oldx > SNAKE_LIMIT)
- big_snake = true;
- fd[d] = x;
- if (odd && bmin <= d && d <= bmax && bd[d] <= x)
- {
- part->xmid = x;
- part->ymid = y;
- part->lo_minimal = part->hi_minimal = true;
- return;
- }
- }
- /* Similarly extend the bottom-up search. */
- if (bmin > dmin)
- bd[--bmin - 1] = OFFSET_MAX;
- else
- ++bmin;
- if (bmax < dmax)
- bd[++bmax + 1] = OFFSET_MAX;
- else
- --bmax;
- for (d = bmax; d >= bmin; d -= 2)
- {
- OFFSET x;
- OFFSET y;
- OFFSET oldx;
- OFFSET tlo = bd[d - 1];
- OFFSET thi = bd[d + 1];
-
- if (tlo < thi)
- x = tlo;
- else
- x = thi - 1;
- oldx = x;
- y = x - d;
- while (x > xoff && y > yoff && xv[x - 1] == yv[y - 1])
- {
- --x;
- --y;
- }
- if (oldx - x > SNAKE_LIMIT)
- big_snake = true;
- bd[d] = x;
- if (!odd && fmin <= d && d <= fmax && x <= fd[d])
- {
- 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
- such, find the one that has made the most progress and return it
- as if it had succeeded.
-
- With this heuristic, for vectors with a constant small density
- of changes, the algorithm is linear in the vector size. */
-
- if (c > 200 && big_snake && ctxt->heuristic)
- {
- OFFSET best;
-
- best = 0;
- for (d = fmax; d >= fmin; d -= 2)
- {
- OFFSET dd = d - fmid;
- OFFSET x = fd[d];
- OFFSET y = x - d;
- OFFSET v = (x - xoff) * 2 - dd;
-
- if (v > 12 * (c + (dd < 0 ? -dd : dd)))
- {
- if (v > best
- && xoff + SNAKE_LIMIT <= x && x < xlim
- && yoff + SNAKE_LIMIT <= y && y < ylim)
- {
- /* We have a good enough best diagonal; now insist
- that it end with a significant snake. */
- int k;
-
- for (k = 1; xv[x - k] == yv[y - k]; k++)
- if (k == SNAKE_LIMIT)
- {
- best = v;
- part->xmid = x;
- part->ymid = y;
- break;
- }
- }
- }
- }
- if (best > 0)
- {
- part->lo_minimal = true;
- part->hi_minimal = false;
- return;
- }
-
- best = 0;
- for (d = bmax; d >= bmin; d -= 2)
- {
- OFFSET dd = d - bmid;
- OFFSET x = bd[d];
- OFFSET y = x - d;
- OFFSET v = (xlim - x) * 2 + dd;
-
- if (v > 12 * (c + (dd < 0 ? -dd : dd)))
- {
- if (v > best
- && xoff < x && x <= xlim - SNAKE_LIMIT
- && yoff < y && y <= ylim - SNAKE_LIMIT)
- {
- /* We have a good enough best diagonal; now insist
- that it end with a significant snake. */
- int k;
-
- for (k = 0; xv[x + k] == yv[y + k]; k++)
- if (k == SNAKE_LIMIT - 1)
- {
- best = v;
- part->xmid = x;
- part->ymid = y;
- break;
- }
- }
- }
- }
- if (best > 0)
- {
- part->lo_minimal = false;
- part->hi_minimal = true;
- 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;
- OFFSET y;
-
- x = MIN (fd[d], xlim);
- 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;
- OFFSET y;
-
- x = MAX (xoff, bd[d]);
- 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;
- }
- }
-}
-
-
-/* Compare in detail contiguous subsequences of the two vectors
- which are known, as a whole, to match each other.
-
- The subsequence of vector 0 is [XOFF, XLIM) and likewise for vector 1.
-
- 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. */
-
-static void
-compareseq (OFFSET xoff, OFFSET xlim, OFFSET yoff, OFFSET ylim,
- bool find_minimal, struct context *ctxt)
-{
- const ELEMENT *const xv = ctxt->xvec; /* Help the compiler. */
- const ELEMENT *const yv = ctxt->yvec;
-
- /* Slide down the bottom initial diagonal. */
- while (xoff < xlim && yoff < ylim && xv[xoff] == yv[yoff])
- {
- ++xoff;
- ++yoff;
- }
-
- /* Slide up the top initial diagonal. */
- while (xlim > xoff && ylim > yoff && xv[xlim - 1] == yv[ylim - 1])
- {
- --xlim;
- --ylim;
- }
-
- /* Handle simple cases. */
- if (xoff == xlim)
- while (yoff < ylim)
- {
- NOTE_INSERT (ctxt, yoff);
- yoff++;
- }
- else if (yoff == ylim)
- while (xoff < xlim)
- {
- NOTE_DELETE (ctxt, xoff);
- xoff++;
- }
- else
- {
- struct partition part;
-
- /* Find a point of correspondence in the middle of the vectors. */
- diag (xoff, xlim, yoff, ylim, find_minimal, &part, ctxt);
-
- /* Use the partitions to split this problem into subproblems. */
- compareseq (xoff, part.xmid, yoff, part.ymid, part.lo_minimal, ctxt);
- compareseq (part.xmid, xlim, part.ymid, ylim, part.hi_minimal, ctxt);
- }
-}
+#include "diffseq.h"
/* Because fstrcmp is typically called multiple times, attempt to minimize
projects / thirdparty / gettext.git / commitdiff
