Merge branch 'pw/xdiff-shrink-memory-consumption' into jch

Shrink wasted memory in Myers diff that does not account for common
prefix and suffix removal.

* pw/xdiff-shrink-memory-consumption:
  xdiff: reduce the size of array
  xprepare: simplify error handling
  xdiff: cleanup xdl_clean_mmatch()
  xdiff: reduce size of action arrays

Author: gitster

xdiff/xprepare.c

@@ -171,12 +171,6 @@ static int xdl_prepare_ctx(unsigned int pass, mmfile_t *mf, long narec, xpparam_
 	if (!XDL_CALLOC_ARRAY(xdf->changed, xdf->nrec + 2))
 		goto abort;
 
-	if ((XDF_DIFF_ALG(xpp->flags) != XDF_PATIENCE_DIFF) &&
-	    (XDF_DIFF_ALG(xpp->flags) != XDF_HISTOGRAM_DIFF)) {
-		if (!XDL_ALLOC_ARRAY(xdf->reference_index, xdf->nrec + 1))
-			goto abort;
-	}
-
 	xdf->changed += 1;
 	xdf->nreff = 0;
 	xdf->dstart = 0;
@@ -197,8 +191,9 @@ void xdl_free_env(xdfenv_t *xe) {
 }
 
 
-static bool xdl_clean_mmatch(uint8_t const *action, ptrdiff_t i, ptrdiff_t s, ptrdiff_t e) {
+static bool xdl_clean_mmatch(uint8_t const *action, ptrdiff_t i, ptrdiff_t len) {
 	ptrdiff_t r, rdis0, rpdis0, rdis1, rpdis1;
+	ptrdiff_t s = 0, e = len - 1;
 
 	/*
 	 * Limits the window that is examined during the similar-lines
@@ -273,16 +268,19 @@ static int xdl_cleanup_records(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xd
 	uint8_t *action1 = NULL, *action2 = NULL;
 	bool need_min = !!(cf->flags & XDF_NEED_MINIMAL);
 	int ret = 0;
+	ptrdiff_t off = xdf1->dstart;
+	ptrdiff_t len1 = xdf1->dend - off + 1;
+	ptrdiff_t len2 = xdf2->dend - off + 1;
 
 	/*
 	 * Create temporary arrays that will help us decide if
 	 * changed[i] should remain false, or become true.
 	 */
-	if (!XDL_CALLOC_ARRAY(action1, xdf1->nrec + 1)) {
-		ret = -1;
-		goto cleanup;
-	}
-	if (!XDL_CALLOC_ARRAY(action2, xdf2->nrec + 1)) {
+	if (!XDL_CALLOC_ARRAY(action1, len1) ||
+	    !XDL_CALLOC_ARRAY(action2, len2) ||
+	    !XDL_ALLOC_ARRAY(xdf1->reference_index, len1) ||
+	    !XDL_ALLOC_ARRAY(xdf2->reference_index, len2))
+	{
 		ret = -1;
 		goto cleanup;
 	}
@@ -299,8 +297,8 @@ static int xdl_cleanup_records(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xd
 	/*
 	 * Initialize temporary arrays with DISCARD, KEEP, or INVESTIGATE.
 	 */
-	for (i = xdf1->dstart; i <= xdf1->dend; i++) {
-		size_t mph1 = xdf1->recs[i].minimal_perfect_hash;
+	for (i = 0; i < len1; i++) {
+		size_t mph1 = xdf1->recs[i + off].minimal_perfect_hash;
 		rcrec = cf->rcrecs[mph1];
 		nm = rcrec ? rcrec->len2 : 0;
 		if (nm == 0)
@@ -311,8 +309,8 @@ static int xdl_cleanup_records(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xd
 			action1[i] = INVESTIGATE;
 	}
 
-	for (i = xdf2->dstart; i <= xdf2->dend; i++) {
-		size_t mph2 = xdf2->recs[i].minimal_perfect_hash;
+	for (i = 0; i < len2; i++) {
+		size_t mph2 = xdf2->recs[i + off].minimal_perfect_hash;
 		rcrec = cf->rcrecs[mph2];
 		nm = rcrec ? rcrec->len1 : 0;
 		if (nm == 0)
@@ -328,25 +326,25 @@ static int xdl_cleanup_records(xdlclassifier_t *cf, xdfile_t *xdf1, xdfile_t *xd
 	 * false, or become true.
 	 */
 	xdf1->nreff = 0;
-	for (i = xdf1->dstart; i <= xdf1->dend; i++) {
+	for (i = 0; i < len1; i++) {
 		if (action1[i] == KEEP ||
-		    (action1[i] == INVESTIGATE && !xdl_clean_mmatch(action1, i, xdf1->dstart, xdf1->dend))) {
-			xdf1->reference_index[xdf1->nreff++] = i;
+		    (action1[i] == INVESTIGATE && !xdl_clean_mmatch(action1, i, len1))) {
+			xdf1->reference_index[xdf1->nreff++] = i + off;
 			/* changed[i] remains false, i.e. keep */
 		} else {
-			xdf1->changed[i] = true;
+			xdf1->changed[i + off] = true;
 			/* i.e. discard */
 		}
 	}
 
 	xdf2->nreff = 0;
-	for (i = xdf2->dstart; i <= xdf2->dend; i++) {
+	for (i = 0; i < len2; i++) {
 		if (action2[i] == KEEP ||
-		    (action2[i] == INVESTIGATE && !xdl_clean_mmatch(action2, i, xdf2->dstart, xdf2->dend))) {
-			xdf2->reference_index[xdf2->nreff++] = i;
+		    (action2[i] == INVESTIGATE && !xdl_clean_mmatch(action2, i, len2))) {
+			xdf2->reference_index[xdf2->nreff++] = i + off;
 			/* changed[i] remains false, i.e. keep */
 		} else {
-			xdf2->changed[i] = true;
+			xdf2->changed[i + off] = true;
 			/* i.e. discard */
 		}
 	}