xdiff: add macros DISCARD(0), KEEP(1), INVESTIGATE(2) in xprepare.c

This commit is refactor-only; no behavior is changed. A future commit
will use bool literals for changed[i].

The functions xdl_clean_mmatch() and xdl_cleanup_records() will be
cleaned up more in a future patch series. The changes to
xdl_cleanup_records(), in this patch, are just to make it clear why
`char rchg` is refactored to `bool changed`.

Rename dis* to action* and replace literal numericals with macros.
The old names came from when dis* (which I think was short for discard)
was treated like a boolean, but over time it grew into a ternary state
machine. The result was confusing because dis* and rchg* both used 0/1
values with different meanings.

The new names and macros make the states explicit. nm is short for
number of matches, and mlim is a heuristic limit:

  nm == 0       -> action[i] = DISCARD     -> changed[i] = true
  0 < nm < mlim -> action[i] = KEEP        -> changed[i] = false
  nm >= mlim    -> action[i] = INVESTIGATE -> changed[i] = xdl_clean_mmatch()

When need_min is true, only DISCARD and KEEP occur because the limit
is effectively infinite.

Best-viewed-with: --color-words
Signed-off-by: Ezekiel Newren <ezekielnewren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/xdiff/xprepare.c b/xdiff/xprepare.c
index b9b19c36dec3d66c412b77ba0023049dd30b2073..55e3b50ce6dfbb9e209ce0c847af0510240292ca 100644 (file)
--- a/xdiff/xprepare.c
+++ b/xdiff/xprepare.c
@@ -29,6 +29,9 @@
 #define XDL_GUESS_NLINES1 256
 #define XDL_GUESS_NLINES2 20
 
+#define DISCARD 0
+#define KEEP 1
+#define INVESTIGATE 2
 
 typedef struct s_xdlclass {
        struct s_xdlclass *next;
@@ -190,15 +193,15 @@ void xdl_free_env(xdfenv_t *xe) {
 }
 
 
-static int xdl_clean_mmatch(char const *dis, long i, long s, long e) {
+static bool xdl_clean_mmatch(uint8_t const *action, long i, long s, long e) {
        long r, rdis0, rpdis0, rdis1, rpdis1;
 
        /*
-        * Limits the window the is examined during the similar-lines
-        * scan. The loops below stops when dis[i - r] == 1 (line that
-        * has no match), but there are corner cases where the loop
-        * proceed all the way to the extremities by causing huge
-        * performance penalties in case of big files.
+        * Limits the window that is examined during the similar-lines
+        * scan. The loops below stops when action[i - r] == KEEP
+        * (line that has no match), but there are corner cases where
+        * the loop proceed all the way to the extremities by causing
+        * huge performance penalties in case of big files.
         */
        if (i - s > XDL_SIMSCAN_WINDOW)
                s = i - XDL_SIMSCAN_WINDOW;
@@ -207,40 +210,47 @@ static int xdl_clean_mmatch(char const *dis, long i, long s, long e) {
 
        /*
         * Scans the lines before 'i' to find a run of lines that either
-        * have no match (dis[j] == 0) or have multiple matches (dis[j] > 1).
-        * Note that we always call this function with dis[i] > 1, so the
-        * current line (i) is already a multimatch line.
+        * have no match (action[j] == DISCARD) or have multiple matches
+        * (action[j] == INVESTIGATE). Note that we always call this
+        * function with action[i] == INVESTIGATE, so the current line
+        * (i) is already a multimatch line.
         */
        for (r = 1, rdis0 = 0, rpdis0 = 1; (i - r) >= s; r++) {
-               if (!dis[i - r])
+               if (action[i - r] == DISCARD)
                        rdis0++;
-               else if (dis[i - r] == 2)
+               else if (action[i - r] == INVESTIGATE)
                        rpdis0++;
-               else
+               else if (action[i - r] == KEEP)
                        break;
+               else
+                       BUG("Illegal value for action[i - r]");
        }
        /*
-        * If the run before the line 'i' found only multimatch lines, we
-        * return 0 and hence we don't make the current line (i) discarded.
-        * We want to discard multimatch lines only when they appear in the
-        * middle of runs with nomatch lines (dis[j] == 0).
+        * If the run before the line 'i' found only multimatch lines,
+        * we return false and hence we don't make the current line (i)
+        * discarded. We want to discard multimatch lines only when
+        * they appear in the middle of runs with nomatch lines
+        * (action[j] == DISCARD).
         */
        if (rdis0 == 0)
                return 0;
        for (r = 1, rdis1 = 0, rpdis1 = 1; (i + r) <= e; r++) {
-               if (!dis[i + r])
+               if (action[i + r] == DISCARD)
                        rdis1++;
-               else if (dis[i + r] == 2)
+               else if (action[i + r] == INVESTIGATE)
                        rpdis1++;
-               else
+               else if (action[i + r] == KEEP)
                        break;
+               else
+                       BUG("Illegal value for action[i + r]");
        }
        /*
-        * If the run after the line 'i' found only multimatch lines, we
-        * return 0 and hence we don't make the current line (i) discarded.
+        * If the run after the line 'i' found only multimatch lines,
+        * we return false and hence we don't make the current line (i)
+        * discarded.
         */
        if (rdis1 == 0)
-               return 0;
+               return false;
        rdis1 += rdis0;
        rpdis1 += rpdis0;
 
@@ -251,26 +261,38 @@ static int xdl_clean_mmatch(char const *dis, long i, long s, long e) {
 /*
  * Try to reduce the problem complexity, discard records that have no
  * matches on the other file. Also, lines that have multiple matches
- * might be potentially discarded if they happear in a run of discardable.
+ * might be potentially discarded if they appear in a run of discardable.
  */
 static int xdl_cleanup_records(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xdf2) {
        long i, nm, nreff, mlim;
        xrecord_t *recs;
        xdlclass_t *rcrec;
-       char *dis, *dis1, *dis2;
-       int need_min = !!(cf->flags & XDF_NEED_MINIMAL);
+       uint8_t *action1 = NULL, *action2 = NULL;
+       bool need_min = !!(cf->flags & XDF_NEED_MINIMAL);
+       int ret = 0;
 
-       if (!XDL_CALLOC_ARRAY(dis, xdf1->nrec + xdf2->nrec + 2))
-               return -1;
-       dis1 = dis;
-       dis2 = dis1 + xdf1->nrec + 1;
+       /*
+        * Create temporary arrays that will help us decide if
+        * changed[i] should remain 0 or become 1.
+        */
+       if (!XDL_CALLOC_ARRAY(action1, xdf1->nrec + 1)) {
+               ret = -1;
+               goto cleanup;
+       }
+       if (!XDL_CALLOC_ARRAY(action2, xdf2->nrec + 1)) {
+               ret = -1;
+               goto cleanup;
+       }
 
+       /*
+        * Initialize temporary arrays with DISCARD, KEEP, or INVESTIGATE.
+        */
        if ((mlim = xdl_bogosqrt(xdf1->nrec)) > XDL_MAX_EQLIMIT)
                mlim = XDL_MAX_EQLIMIT;
        for (i = xdf1->dstart, recs = &xdf1->recs[xdf1->dstart]; i <= xdf1->dend; i++, recs++) {
                rcrec = cf->rcrecs[recs->ha];
                nm = rcrec ? rcrec->len2 : 0;
-               dis1[i] = (nm == 0) ? 0: (nm >= mlim && !need_min) ? 2: 1;
+               action1[i] = (nm == 0) ? DISCARD: (nm >= mlim && !need_min) ? INVESTIGATE: KEEP;
        }
 
        if ((mlim = xdl_bogosqrt(xdf2->nrec)) > XDL_MAX_EQLIMIT)
@@ -278,32 +300,42 @@ static int xdl_cleanup_records(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xd
        for (i = xdf2->dstart, recs = &xdf2->recs[xdf2->dstart]; i <= xdf2->dend; i++, recs++) {
                rcrec = cf->rcrecs[recs->ha];
                nm = rcrec ? rcrec->len1 : 0;
-               dis2[i] = (nm == 0) ? 0: (nm >= mlim && !need_min) ? 2: 1;
+               action2[i] = (nm == 0) ? DISCARD: (nm >= mlim && !need_min) ? INVESTIGATE: KEEP;
        }
 
+       /*
+        * Use temporary arrays to decide if changed[i] should remain
+        * 0 or become 1.
+        */
        for (nreff = 0, i = xdf1->dstart, recs = &xdf1->recs[xdf1->dstart];
             i <= xdf1->dend; i++, recs++) {
-               if (dis1[i] == 1 ||
-                   (dis1[i] == 2 && !xdl_clean_mmatch(dis1, i, xdf1->dstart, xdf1->dend))) {
+               if (action1[i] == KEEP ||
+                   (action1[i] == INVESTIGATE && !xdl_clean_mmatch(action1, i, xdf1->dstart, xdf1->dend))) {
                        xdf1->rindex[nreff++] = i;
+                       /* changed[i] remains 0, i.e. keep */
                } else
                        xdf1->changed[i] = 1;
+                       /* i.e. discard */
        }
        xdf1->nreff = nreff;
 
        for (nreff = 0, i = xdf2->dstart, recs = &xdf2->recs[xdf2->dstart];
             i <= xdf2->dend; i++, recs++) {
-               if (dis2[i] == 1 ||
-                   (dis2[i] == 2 && !xdl_clean_mmatch(dis2, i, xdf2->dstart, xdf2->dend))) {
+               if (action2[i] == KEEP ||
+                   (action2[i] == INVESTIGATE && !xdl_clean_mmatch(action2, i, xdf2->dstart, xdf2->dend))) {
                        xdf2->rindex[nreff++] = i;
+                       /* changed[i] remains 0, i.e. keep */
                } else
                        xdf2->changed[i] = 1;
+                       /* i.e. discard */
        }
        xdf2->nreff = nreff;
 
-       xdl_free(dis);
+cleanup:
+       xdl_free(action1);
+       xdl_free(action2);
 
-       return 0;
+       return ret;
 }