xdiff: introduce XDL_ALLOC_GROW()
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. Note that xdl_alloc_grow_helper() uses long rather than size_t for `nr` and `alloc` to match the existing code. Signed-off-by: Phillip Wood <phillip.wood@dunelm.org.uk> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Phillip Wood committed
Jul 8, 2022 at 16:25 UTC
f7b587bf656574103a0a2ad9c2337b0d15c0e92d
4 files changed
+33
-16
xdiff/xmacros.h
+10
@@ -58,4 +58,14 @@ do { \
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/* Allocate an array of nr zeroed out elements, returns NULL on failure */
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#define XDL_CALLOC_ARRAY(p, nr) ((p) = xdl_calloc(nr, sizeof(*(p))))
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+/*
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+ * Ensure array p can accommodate at least nr elements, growing the
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+ * array and updating alloc (which is the number of allocated
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+ * elements) as necessary. Frees p and returns -1 on failure, returns
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+ * 0 on success
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+ */
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+#define XDL_ALLOC_GROW(p, nr, alloc) \
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+ (-!((nr) <= (alloc) || \
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+ ((p) = xdl_alloc_grow_helper((p), (nr), &(alloc), sizeof(*(p))))))
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+
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#endif /* #if !defined(XMACROS_H) */
xdiff/xprepare.c
+4
-15
@@ -111,7 +111,6 @@ static int xdl_classify_record(unsigned int pass, xdlclassifier_t *cf, xrecord_t
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long hi;
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char const *line;
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xdlclass_t *rcrec;
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- xdlclass_t **rcrecs;
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line = rec->ptr;
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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
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return -1;
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}
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rcrec->idx = cf->count++;
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- if (cf->count > cf->alloc) {
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- cf->alloc *= 2;
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- if (!(rcrecs = (xdlclass_t **) xdl_realloc(cf->rcrecs, cf->alloc * sizeof(xdlclass_t *)))) {
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-
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+ if (XDL_ALLOC_GROW(cf->rcrecs, cf->count, cf->alloc))
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return -1;
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- }
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- cf->rcrecs = rcrecs;
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- }
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cf->rcrecs[rcrec->idx] = rcrec;
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rcrec->line = line;
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rcrec->size = rec->size;
@@ -163,7 +156,7 @@ static int xdl_prepare_ctx(unsigned int pass, mmfile_t *mf, long narec, xpparam_
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unsigned long hav;
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char const *blk, *cur, *top, *prev;
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xrecord_t *crec;
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- xrecord_t **recs, **rrecs;
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+ xrecord_t **recs;
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xrecord_t **rhash;
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unsigned long *ha;
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char *rchg;
@@ -190,12 +183,8 @@ static int xdl_prepare_ctx(unsigned int pass, mmfile_t *mf, long narec, xpparam_
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for (top = blk + bsize; cur < top; ) {
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prev = cur;
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hav = xdl_hash_record(&cur, top, xpp->flags);
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- if (nrec >= narec) {
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- narec *= 2;
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- if (!(rrecs = (xrecord_t **) xdl_realloc(recs, narec * sizeof(xrecord_t *))))
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- goto abort;
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- recs = rrecs;
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- }
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+ if (XDL_ALLOC_GROW(recs, nrec + 1, narec))
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+ goto abort;
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if (!(crec = xdl_cha_alloc(&xdf->rcha)))
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goto abort;
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crec->ptr = prev;
xdiff/xutils.c
+17
@@ -432,3 +432,20 @@ int xdl_fall_back_diff(xdfenv_t *diff_env, xpparam_t const *xpp,
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return 0;
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}
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+
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+void* xdl_alloc_grow_helper(void *p, long nr, long *alloc, size_t size)
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+{
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+ void *tmp = NULL;
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+ size_t n = ((LONG_MAX - 16) / 2 >= *alloc) ? 2 * *alloc + 16 : LONG_MAX;
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+ if (nr > n)
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+ n = nr;
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+ if (SIZE_MAX / size >= n)
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+ tmp = xdl_realloc(p, n * size);
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+ if (tmp) {
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+ *alloc = n;
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+ } else {
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+ xdl_free(p);
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+ *alloc = 0;
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+ }
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+ return tmp;
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+}
xdiff/xutils.h
+2
-1
@@ -42,6 +42,7 @@ int xdl_emit_hunk_hdr(long s1, long c1, long s2, long c2,
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int xdl_fall_back_diff(xdfenv_t *diff_env, xpparam_t const *xpp,
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int line1, int count1, int line2, int count2);
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-
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+/* Do not call this function, use XDL_ALLOC_GROW instead */
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+void* xdl_alloc_grow_helper(void* p, long nr, long* alloc, size_t size);
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#endif /* #if !defined(XUTILS_H) */