Re: [PATCH] blame.c: prepare_lines should not call xrealloc for every line

[Junio C Hamano <gitster@pobox.com>]

Junio C Hamano <gitster@pobox.com> writes:

> David Kastrup <dak@gnu.org> writes:
>
>> Whitespace error in line 1778.  Should I be reposting?
>
> Heh, let me try to clean it up first and then repost for your
> review.
>
> Thanks.

-- >8 --
From: David Kastrup <dak@gnu.org>

Making a single preparation run for counting the lines will avoid memory
fragmentation.  Also, fix the allocated memory size which was wrong
when sizeof(int *) != sizeof(int), and would have been too small
for sizeof(int *) < sizeof(int), admittedly unlikely.

Signed-off-by: David Kastrup <dak@gnu.org>
---

 One logic difference from what was posted is that sb->lineno[num]
 is filled with the length of the entire buffer when the file ends
 with a complete line.  I do not remember if the rest of the logic
 actually depends on it (I think I use lineno[n+1] - lineno[n] to
 find the end of line, so this may matter for the last line),
 though.

 The original code dates back to 2006 when the author of the code
 was not paid for doing anything for Git but was doing it as a
 weekend and evening hobby, so it may not be so surprising to find
 this kind of "what was I thinking when I wrote it" inefficiency in
 such a code with $0 monetary value ;-)

 builtin/blame.c | 37 +++++++++++++++++++++----------------
 1 file changed, 21 insertions(+), 16 deletions(-)

diff --git a/builtin/blame.c b/builtin/blame.c
index e44a6bb..2364661 100644
--- a/builtin/blame.c
+++ b/builtin/blame.c
@@ -1772,25 +1772,30 @@ static int prepare_lines(struct scoreboard *sb)
 {
 	const char *buf = sb->final_buf;
 	unsigned long len = sb->final_buf_size;
-	int num = 0, incomplete = 0, bol = 1;
+	const char *end = buf + len;
+	const char *p;
+	int *lineno;
+	int num = 0, incomplete = 0;
+
+	for (p = buf; p < end; p++) {
+		p = memchr(p, '\n', end - p);
+		if (!p)
+			break;
+		num++;
+	}
 
-	if (len && buf[len-1] != '\n')
+	if (len && end[-1] != '\n')
 		incomplete++; /* incomplete line at the end */
-	while (len--) {
-		if (bol) {
-			sb->lineno = xrealloc(sb->lineno,
-					      sizeof(int *) * (num + 1));
-			sb->lineno[num] = buf - sb->final_buf;
-			bol = 0;
-		}
-		if (*buf++ == '\n') {
-			num++;
-			bol = 1;
-		}
+
+	sb->lineno = lineno = xmalloc(sizeof(int) * (num + incomplete + 1));
+
+	for (p = buf; p < end; p++) {
+		*lineno++ = p - buf;
+		p = memchr(p, '\n', end - p);
+		if (!p)
+			break;
 	}
-	sb->lineno = xrealloc(sb->lineno,
-			      sizeof(int *) * (num + incomplete + 1));
-	sb->lineno[num + incomplete] = buf - sb->final_buf;
+	sb->lineno[num + incomplete] = len;
 	sb->num_lines = num + incomplete;
 	return sb->num_lines;
 }