[PATCH 18/21] strbuf: allow "buf" to point to the middle of the allocated buffer

From

Nguyễn Thái Ngọc Duy <pclouds@gmail.com>

Date

Dec 15, 2010, 15:02 UTC

Message-ID

<1292425376-14550-19-git-send-email-pclouds@gmail.com>

In-Reply-To

<1292425376-14550-1-git-send-email-pclouds@gmail.com>

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 strbuf.c |   36 ++++++++++++++++++++++++++----------
 strbuf.h |   10 ++++++----
 2 files changed, 32 insertions(+), 14 deletions(-)

diff --git a/strbuf.c b/strbuf.c
index bc3a080..12cda6f 100644
--- a/strbuf.c
+++ b/strbuf.c
@@ -28,8 +28,10 @@ char strbuf_slopbuf[1];
 
 void strbuf_init(struct strbuf *sb, size_t hint)
 {
-	sb->alloc = sb->len = 0;
-	sb->buf = strbuf_slopbuf;
+	sb->alloc  = 0;
+	sb->len	   = 0;
+	sb->neglen = 0;
+	sb->buf	   = strbuf_slopbuf;
 	if (hint)
 		strbuf_grow(sb, hint);
 }
@@ -37,7 +39,7 @@ void strbuf_init(struct strbuf *sb, size_t hint)
 void strbuf_release(struct strbuf *sb)
 {
 	if (sb->alloc) {
-		free(sb->buf);
+		free(sb->buf - sb->neglen);
 		strbuf_init(sb, 0);
 	}
 }
@@ -45,6 +47,8 @@ void strbuf_release(struct strbuf *sb)
 char *strbuf_detach(struct strbuf *sb, size_t *sz)
 {
 	char *res = sb->alloc ? sb->buf : NULL;
+	if (sb->neglen)
+		die("shift buf back before detaching");
 	if (sz)
 		*sz = sb->len;
 	strbuf_init(sb, 0);
@@ -54,20 +58,23 @@ char *strbuf_detach(struct strbuf *sb, size_t *sz)
 void strbuf_attach(struct strbuf *sb, void *buf, size_t len, size_t alloc)
 {
 	strbuf_release(sb);
-	sb->buf   = buf;
-	sb->len   = len;
-	sb->alloc = alloc;
+	sb->buf    = buf;
+	sb->len    = len;
+	sb->neglen = 0;
+	sb->alloc  = alloc;
 	strbuf_grow(sb, 0);
 	sb->buf[sb->len] = '\0';
 }
 
 void strbuf_grow(struct strbuf *sb, size_t extra)
 {
-	if (sb->len + extra + 1 <= sb->len)
+	char *buf = !sb->alloc ? NULL : sb->buf - sb->neglen;
+	int len = sb->neglen + sb->len;
+
+	if (len + extra + 1 <= len)
 		die("you want to use way too much memory");
-	if (!sb->alloc)
-		sb->buf = NULL;
-	ALLOC_GROW(sb->buf, sb->len + extra + 1, sb->alloc);
+	ALLOC_GROW(buf, len + extra + 1, sb->alloc);
+	sb->buf = buf + sb->neglen;
 }
 
 void strbuf_trim(struct strbuf *sb)
@@ -402,3 +409,12 @@ int strbuf_check_branch_ref(struct strbuf *sb, const char *name)
 	strbuf_splice(sb, 0, 0, "refs/heads/", 11);
 	return check_ref_format(sb->buf);
 }
+
+void strbuf_offset(struct strbuf *sb, int offset)
+{
+	if (offset > sb->len || offset < sb->neglen)
+		die("you cannot offset out of allocated buffer");
+	sb->buf	   += offset;
+	sb->neglen += offset;
+	sb->len	   -= offset;
+}
diff --git a/strbuf.h b/strbuf.h
index fac2dbc..3c3b146 100644
--- a/strbuf.h
+++ b/strbuf.h
@@ -43,11 +43,11 @@
 extern char strbuf_slopbuf[];
 struct strbuf {
 	size_t alloc;
-	size_t len;
+	size_t len, neglen;
 	char *buf;
 };
 
-#define STRBUF_INIT  { 0, 0, strbuf_slopbuf }
+#define STRBUF_INIT  { 0, 0, 0, strbuf_slopbuf }
 
 /*----- strbuf life cycle -----*/
 extern void strbuf_init(struct strbuf *, size_t);
@@ -62,7 +62,7 @@ static inline void strbuf_swap(struct strbuf *a, struct strbuf *b) {
 
 /*----- strbuf size related -----*/
 static inline size_t strbuf_avail(const struct strbuf *sb) {
-	return sb->alloc ? sb->alloc - sb->len - 1 : 0;
+	return sb->alloc ? sb->alloc - sb->len - sb->neglen - 1 : 0;
 }
 
 extern void strbuf_grow(struct strbuf *, size_t);
@@ -70,7 +70,7 @@ extern void strbuf_grow(struct strbuf *, size_t);
 static inline void strbuf_setlen(struct strbuf *sb, size_t len) {
 	if (!sb->alloc)
 		strbuf_grow(sb, 0);
-	assert(len < sb->alloc);
+	assert(sb->neglen + len < sb->alloc);
 	sb->len = len;
 	sb->buf[len] = '\0';
 }
@@ -136,4 +136,6 @@ extern int launch_editor(const char *path, struct strbuf *buffer, const char *co
 extern int strbuf_branchname(struct strbuf *sb, const char *name);
 extern int strbuf_check_branch_ref(struct strbuf *sb, const char *name);
 
+extern void strbuf_offset(struct strbuf *sb, int offset);
+
 #endif /* STRBUF_H */

-- 
1.7.3.3.476.g10a82