builtin-apply.c: clean-up apply_one_fragment()

We had two pointer variables pointing to the same buffer and an
integer variable used to index into its tail part that was
active (old, oldlines and oldsize for the preimage, and their
'new' counterparts for the postimage).

To help readability, use 'oldlines' as the allocated pointer,
and use 'old' as the pointer to the tail that advances while the
code builds up the contents in the buffer.  The size 'oldsize'
can be computed as (old-oldines).

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-apply.c

@@ -1804,10 +1804,7 @@ static int apply_one_fragment(struct image *img, struct fragment *frag,
 	int match_beginning, match_end;
 	const char *patch = frag->patch;
 	int size = frag->size;
-	char *old = xmalloc(size);
-	char *new = xmalloc(size);
-	char *oldlines, *newlines;
-	int oldsize = 0, newsize = 0;
+	char *old, *new, *oldlines, *newlines;
 	int new_blank_lines_at_end = 0;
 	unsigned long leading, trailing;
 	int pos, applied_pos;
@@ -1816,7 +1813,11 @@ static int apply_one_fragment(struct image *img, struct fragment *frag,
 
 	memset(&preimage, 0, sizeof(preimage));
 	memset(&postimage, 0, sizeof(postimage));
+	oldlines = xmalloc(size);
+	newlines = xmalloc(size);
 
+	old = oldlines;
+	new = newlines;
 	while (size > 0) {
 		char first;
 		int len = linelen(patch, size);
@@ -1833,7 +1834,7 @@ static int apply_one_fragment(struct image *img, struct fragment *frag,
 		 * followed by "\ No newline", then we also remove the
 		 * last one (which is the newline, of course).
 		 */
-		plen = len-1;
+		plen = len - 1;
 		if (len < size && patch[len] == '\\')
 			plen--;
 		first = *patch;
@@ -1850,30 +1851,30 @@ static int apply_one_fragment(struct image *img, struct fragment *frag,
 			if (plen < 0)
 				/* ... followed by '\No newline'; nothing */
 				break;
-			old[oldsize++] = '\n';
-			new[newsize++] = '\n';
+			*old++ = '\n';
+			*new++ = '\n';
 			add_line_info(&preimage, "\n", 1, LINE_COMMON);
 			add_line_info(&postimage, "\n", 1, LINE_COMMON);
 			break;
 		case ' ':
 		case '-':
-			memcpy(old + oldsize, patch + 1, plen);
-			add_line_info(&preimage, old + oldsize, plen,
+			memcpy(old, patch + 1, plen);
+			add_line_info(&preimage, old, plen,
 				      (first == ' ' ? LINE_COMMON : 0));
-			oldsize += plen;
+			old += plen;
 			if (first == '-')
 				break;
 		/* Fall-through for ' ' */
 		case '+':
 			if (first != '+' || !no_add) {
-				int added = apply_line(new + newsize, patch,
+				int added = apply_line(new, patch,
 						       plen, ws_rule);
-				add_line_info(&postimage, new + newsize, added,
+				add_line_info(&postimage, new, added,
 					      (first == '+' ? 0 : LINE_COMMON));
 
-				newsize += added;
+				new += added;
 				if (first == '+' &&
-				    added == 1 && new[newsize-1] == '\n')
+				    added == 1 && new[-1] == '\n')
 					added_blank_line = 1;
 			}
 			break;
@@ -1892,16 +1893,13 @@ static int apply_one_fragment(struct image *img, struct fragment *frag,
 		patch += len;
 		size -= len;
 	}
-
 	if (inaccurate_eof &&
-	    oldsize > 0 && old[oldsize - 1] == '\n' &&
-	    newsize > 0 && new[newsize - 1] == '\n') {
-		oldsize--;
-		newsize--;
+	    old > oldlines && old[-1] == '\n' &&
+	    new > newlines && new[-1] == '\n') {
+		old--;
+		new--;
 	}
 
-	oldlines = old;
-	newlines = new;
 	leading = frag->leading;
 	trailing = frag->trailing;
 
@@ -1923,10 +1921,10 @@ static int apply_one_fragment(struct image *img, struct fragment *frag,
 	}
 
 	pos = frag->newpos ? (frag->newpos - 1) : 0;
-	preimage.buf = old;
-	preimage.len = oldsize;
-	postimage.buf = new;
-	postimage.len = newsize;
+	preimage.buf = oldlines;
+	preimage.len = old - oldlines;
+	postimage.buf = newlines;
+	postimage.len = new - newlines;
 	preimage.line = preimage.line_allocated;
 	postimage.line = postimage.line_allocated;
 
@@ -1990,11 +1988,12 @@ static int apply_one_fragment(struct image *img, struct fragment *frag,
 		update_image(img, applied_pos, &preimage, &postimage);
 	} else {
 		if (apply_verbosely)
-			error("while searching for:\n%.*s", oldsize, oldlines);
+			error("while searching for:\n%.*s",
+			      (int)(old - oldlines), oldlines);
 	}
 
-	free(old);
-	free(new);
+	free(oldlines);
+	free(newlines);
 	free(preimage.line_allocated);
 	free(postimage.line_allocated);