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[PATCH 3/3] xdiff: introduce XDL_ALLOC_GROW()

From
PGPhillip Wood via GitGitGadget <gitgitgadget@gmail.com>
Date
Jun 29, 2022, 15:25 UTC
Message-ID
<da996677f0730ec7a50d399524fb58c44dad468a.1656516334.git.gitgitgadget@gmail.com>
In-Reply-To
<pull.1272.git.1656516334.gitgitgadget@gmail.com>
From: Phillip Wood <phillip.wood@dunelm.org.uk>

Add a helper to grow an array. This is analogous to ALLOC_GROW() in the rest of the codebase but returns −1 on allocation failure to accommodate other users of libxdiff such as libgit2. It will also return a error if the multiplication overflows while calculating the new allocation size. Note that this keeps doubling on reallocation like the code it is replacing rather than increasing the existing size by half like ALLOC_GROW(). It does however copy ALLOC_GROW()'s trick of adding a small amount to the new allocation to avoid a lot of reallocations at small sizes.

Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk>
---
 xdiff/xmacros.h  | 10 ++++++++++
 xdiff/xprepare.c | 19 ++++---------------
 xdiff/xutils.c   | 17 +++++++++++++++++
 xdiff/xutils.h   |  3 ++-
 4 files changed, 33 insertions(+), 16 deletions(-)
diff --git a/xdiff/xmacros.h b/xdiff/xmacros.h
index 23db8e785d7..d13a6724629 100644
--- a/xdiff/xmacros.h
+++ b/xdiff/xmacros.h
@@ -61,4 +61,14 @@ do { \
 		? memset((p), 0, (nr) * sizeof(*(p)))	\
 		: NULL)
 
+/*
+ * Ensure array p can accommodate at least nr elements, growing the
+ * array and updating alloc (which is the number of allocated
+ * elements) as necessary. Frees p and returns -1 on failure, returns
+ * 0 on success
+ */
+#define XDL_ALLOC_GROW(p, nr, alloc)	\
+	(-!((nr) <= (alloc) ||		\
+	    ((p) = xdl_alloc_grow_helper((p), (nr), &(alloc), sizeof(*(p))))))
+
 #endif /* #if !defined(XMACROS_H) */
diff --git a/xdiff/xprepare.c b/xdiff/xprepare.c
index b016570c488..c84549f6c50 100644
--- a/xdiff/xprepare.c
+++ b/xdiff/xprepare.c
@@ -111,7 +111,6 @@ static int xdl_classify_record(unsigned int pass, xdlclassifier_t *cf, xrecord_t
 	long hi;
 	char const *line;
 	xdlclass_t *rcrec;
-	xdlclass_t **rcrecs;
 
 	line = rec->ptr;
 	hi = (long) XDL_HASHLONG(rec->ha, cf->hbits);
@@ -127,14 +126,8 @@ static int xdl_classify_record(unsigned int pass, xdlclassifier_t *cf, xrecord_t
 			return -1;
 		}
 		rcrec->idx = cf->count++;
-		if (cf->count > cf->alloc) {
-			cf->alloc *= 2;
-			if (!(rcrecs = (xdlclass_t **) xdl_realloc(cf->rcrecs, cf->alloc * sizeof(xdlclass_t *)))) {
-
+		if (XDL_ALLOC_GROW(cf->rcrecs, cf->count, cf->alloc))
 				return -1;
-			}
-			cf->rcrecs = rcrecs;
-		}
 		cf->rcrecs[rcrec->idx] = rcrec;
 		rcrec->line = line;
 		rcrec->size = rec->size;
@@ -163,7 +156,7 @@ static int xdl_prepare_ctx(unsigned int pass, mmfile_t *mf, long narec, xpparam_
 	unsigned long hav;
 	char const *blk, *cur, *top, *prev;
 	xrecord_t *crec;
-	xrecord_t **recs, **rrecs;
+	xrecord_t **recs;
 	xrecord_t **rhash;
 	unsigned long *ha;
 	char *rchg;
@@ -190,12 +183,8 @@ static int xdl_prepare_ctx(unsigned int pass, mmfile_t *mf, long narec, xpparam_
 		for (top = blk + bsize; cur < top; ) {
 			prev = cur;
 			hav = xdl_hash_record(&cur, top, xpp->flags);
-			if (nrec >= narec) {
-				narec *= 2;
-				if (!(rrecs = (xrecord_t **) xdl_realloc(recs, narec * sizeof(xrecord_t *))))
-					goto abort;
-				recs = rrecs;
-			}
+			if (XDL_ALLOC_GROW(recs, nrec + 1, narec))
+				goto abort;
 			if (!(crec = xdl_cha_alloc(&xdf->rcha)))
 				goto abort;
 			crec->ptr = prev;
diff --git a/xdiff/xutils.c b/xdiff/xutils.c
index 115b2b1640b..9e36f24875d 100644
--- a/xdiff/xutils.c
+++ b/xdiff/xutils.c
@@ -432,3 +432,20 @@ int xdl_fall_back_diff(xdfenv_t *diff_env, xpparam_t const *xpp,
 
 	return 0;
 }
+
+void* xdl_alloc_grow_helper(void *p, long nr, long *alloc, size_t size)
+{
+	void *tmp = NULL;
+	size_t n = ((LONG_MAX - 16) / 2 >= *alloc) ? 2 * *alloc + 16 : LONG_MAX;
+	if (nr > n)
+		n = nr;
+	if (SIZE_MAX / size >= n)
+		tmp = xdl_realloc(p, n * size);
+	if (tmp) {
+		*alloc = n;
+	} else {
+		xdl_free(p);
+		*alloc = 0;
+	}
+	return tmp;
+}
diff --git a/xdiff/xutils.h b/xdiff/xutils.h
index fba7bae03c7..fd0bba94e8b 100644
--- a/xdiff/xutils.h
+++ b/xdiff/xutils.h
@@ -42,6 +42,7 @@ int xdl_emit_hunk_hdr(long s1, long c1, long s2, long c2,
 int xdl_fall_back_diff(xdfenv_t *diff_env, xpparam_t const *xpp,
 		       int line1, int count1, int line2, int count2);
 
-
+/* Do not call this function, use XDL_ALLOC_GROW instead */
+void* xdl_alloc_grow_helper(void* p, long nr, long* alloc, size_t size);
 
 #endif /* #if !defined(XUTILS_H) */

-- 
gitgitgadget
Previous: Phillip WoodNext: Ævar Arnfjörð Bjarmason
Message 6 of 52 in “xdiff: introduce memory allocation macros”
  1. 0/3 xdiff: introduce memory allocation macrosPhillip Wood via GitGitGadget, Jun 29, 2022
  2. 1/3 xdiff: introduce XDL_ALLOC_ARRAY()Phillip Wood via GitGitGadget, Jun 29, 2022
  3. 2/3 xdiff: introduce XDL_CALLOC_ARRAY()Phillip Wood via GitGitGadget, Jun 29, 2022
  4. Junio C HamanoJun 30, 2022
  5. Phillip WoodJul 6, 2022
  6. 3/3 xdiff: introduce XDL_ALLOC_GROW()Phillip Wood via GitGitGadget, Jun 29, 2022
  7. Ævar Arnfjörð BjarmasonJun 30, 2022
  8. Phillip WoodJun 30, 2022
  9. Phillip WoodJun 30, 2022
  10. Ævar Arnfjörð BjarmasonJun 30, 2022
  11. Phillip WoodJul 6, 2022
  12. Ævar Arnfjörð BjarmasonJul 7, 2022
  13. Phillip WoodJul 8, 2022
  14. 0/7 xdiff: use standard alloc macros, share them via git-shared-util.hÆvar Arnfjörð Bjarmason, Jul 8, 2022
  15. 1/7 xdiff: simplify freeing patterns around xdl_free_env()Ævar Arnfjörð Bjarmason, Jul 8, 2022
  16. 2/7 git-shared-util.h: move "shared" allocation utilities hereÆvar Arnfjörð Bjarmason, Jul 8, 2022
  17. 3/7 git-shared-util.h: add G*() versions of *ALLOC_*()Ævar Arnfjörð Bjarmason, Jul 8, 2022
  18. Phillip WoodJul 11, 2022
  19. 5/7 xdiff: use GALLOC_GROW(), not XDL_ALLOC_GROW()Ævar Arnfjörð Bjarmason, Jul 8, 2022
  20. Phillip WoodJul 11, 2022
  21. Ævar Arnfjörð BjarmasonJul 11, 2022
  22. Phillip WoodJul 13, 2022
  23. Ævar Arnfjörð BjarmasonJul 13, 2022
  24. Phillip WoodJul 13, 2022
  25. 4/7 xdiff: use G[C]ALLOC_ARRAY(), not XDL_CALLOC_ARRAY()Ævar Arnfjörð Bjarmason, Jul 8, 2022
  26. Phillip WoodJul 11, 2022
  27. 6/7 xdiff: remove xdl_malloc() wrapper, use malloc(), not xmalloc()Ævar Arnfjörð Bjarmason, Jul 8, 2022
  28. Phillip WoodJul 8, 2022
  29. Ævar Arnfjörð BjarmasonJul 8, 2022
  30. Jeff KingJul 8, 2022
  31. Ævar Arnfjörð BjarmasonJul 8, 2022
  32. Jeff KingJul 11, 2022
  33. 7/7 xdiff: remove xdl_free(), use free() insteadÆvar Arnfjörð Bjarmason, Jul 8, 2022
  34. Phillip WoodJul 8, 2022
  35. Ævar Arnfjörð BjarmasonJul 8, 2022
  36. Phillip WoodJul 11, 2022
  37. Phillip WoodJul 11, 2022
  38. Ævar Arnfjörð BjarmasonJul 11, 2022
  39. Phillip WoodJul 13, 2022
  40. Ævar Arnfjörð BjarmasonJul 13, 2022
  41. Junio C HamanoJun 30, 2022
  42. Phillip WoodJul 6, 2022
  43. Ævar Arnfjörð BjarmasonJun 30, 2022
  44. 0/4 xdiff: introduce memory allocation macrosPhillip Wood via GitGitGadget, Jul 8, 2022
  45. 2/4 xdiff: introduce xdl_callocPhillip Wood via GitGitGadget, Jul 8, 2022
  46. 1/4 xdiff: introduce XDL_ALLOC_ARRAY()Phillip Wood via GitGitGadget, Jul 8, 2022
  47. 4/4 xdiff: introduce XDL_ALLOC_GROW()Phillip Wood via GitGitGadget, Jul 8, 2022
  48. Ævar Arnfjörð BjarmasonJul 8, 2022
  49. Phillip WoodJul 11, 2022
  50. Jeff KingJul 12, 2022
  51. Phillip WoodJul 13, 2022
  52. 3/4 xdiff: introduce XDL_CALLOC_ARRAY()Phillip Wood via GitGitGadget, Jul 8, 2022

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