From: Andre Noll <maan@systemlinux.org>
Date: Tue, 9 Aug 2011 18:00:12 +0000 (+0200)
Subject: btr: Introduce btr_next_buffer_omit().
X-Git-Tag: v0.4.9~2^2~4
X-Git-Url: http://git.tuebingen.mpg.de/?p=paraslash.git;a=commitdiff_plain;h=4c5110988155bd46629a0833a1887f2075257e38

btr: Introduce btr_next_buffer_omit().

This function is useful for the flac decoder.
---

diff --git a/buffer_tree.c b/buffer_tree.c
index 88fb8362..cb9d514f 100644
--- a/buffer_tree.c
+++ b/buffer_tree.c
@@ -563,40 +563,95 @@ static size_t btr_get_buffer_by_reference(struct btr_buffer_reference *br, char
 }
 
 /**
- * Obtain the next buffer of the input queue of a buffer tree node.
+ * Obtain the next buffer of the input queue, omitting data.
  *
  * \param btrn The node whose input queue is to be queried.
+ * \param omit Number of bytes to be omitted.
  * \param bufp Result pointer.
  *
- * \return The number of bytes that can be read from buf. Zero if the input
- * buffer queue is empty. In this case the value of \a bufp is undefined.
+ * If a buffer tree node needs more input data but can not consume the data it
+ * already has (because it might be needed again later) this function can be
+ * used instead of btr_next_buffer() to get a reference to the buffer obtained
+ * by skipping the given number of bytes. Skipped input bytes are not consumed.
+ *
+ * With a zero \a omit argument, this function is equivalent to \ref
+ * btr_next_buffer().
+ *
+ * \return Number of bytes in \a bufp. If there are less than or equal to \a
+ * omit many bytes available in the input queue of the buffer tree node pointed
+ * to by \a btrn, the function returns zero and the value of \a bufp is
+ * undefined.
  */
-size_t btr_next_buffer(struct btr_node *btrn, char **bufp)
+size_t btr_next_buffer_omit(struct btr_node *btrn, size_t omit, char **bufp)
 {
 	struct btr_buffer_reference *br;
+	size_t wrap_count, sz, rv = 0;
 	char *buf, *result = NULL;
-	size_t sz, rv = 0;
 
-	FOR_EACH_BUFFER_REF(br, btrn) {
+	br = get_first_input_br(btrn);
+	if (!br)
+		return 0;
+	wrap_count = br->wrap_count;
+	if (wrap_count > 0) { /* we have a wrap buffer */
 		sz = btr_get_buffer_by_reference(br, &buf);
-		if (!result) {
-			result = buf;
-			rv = sz;
-			if (!br->btrb->pool)
-				break;
-			continue;
+		if (sz > omit) { /* and it's big enough */
+			result = buf + omit;
+			rv = sz - omit;
+			/*
+			 * Wrap buffers are allocated by malloc(), so the next
+			 * buffer ref will not align nicely, so we return the
+			 * tail of the wrap buffer.
+			 */
+			goto out;
 		}
-		if (!br->btrb->pool)
-			break;
-		if (result + rv != buf)
-			break;
-		rv += sz;
+		/*
+		 * The next wrap_count bytes exist twice, in the wrap buffer
+		 * and as a buffer reference in the buffer tree pool.
+		 */
+		omit += wrap_count;
+	}
+	/*
+	 * For buffer tree pools, the buffers in the list align, i.e. the next
+	 * buffer in the list starts directly at the end of its predecessor. In
+	 * this case we merge adjacent buffers and return one larger buffer
+	 * instead.
+	 */
+	FOR_EACH_BUFFER_REF(br, btrn) {
+		sz = btr_get_buffer_by_reference(br, &buf);
+		if (result) {
+			if (result + rv != buf)
+				goto out;
+			rv += sz;
+		} else if (sz > omit) {
+			result = buf + omit;
+			rv = sz - omit;
+		} else
+			omit -= sz;
 	}
+	if (!result)
+		return 0;
+out:
 	if (bufp)
 		*bufp = result;
 	return rv;
 }
 
+/**
+ * Obtain the next buffer of the input queue of a buffer tree node.
+ *
+ * \param btrn The node whose input queue is to be queried.
+ * \param bufp Result pointer.
+ *
+ * \return The number of bytes that can be read from buf.
+ *
+ * The call of this function is is equivalent to calling \ref
+ * btr_next_buffer_omit() with an \a omit value of zero.
+ */
+size_t btr_next_buffer(struct btr_node *btrn, char **bufp)
+{
+	return btr_next_buffer_omit(btrn, 0, bufp);
+}
+
 /**
  * Deallocate the given number of bytes from the input queue.
  *
diff --git a/buffer_tree.h b/buffer_tree.h
index fcf9df62..b60751e5 100644
--- a/buffer_tree.h
+++ b/buffer_tree.h
@@ -189,6 +189,7 @@ size_t btr_get_input_queue_size(struct btr_node *btrn);
 size_t btr_get_output_queue_size(struct btr_node *btrn);
 bool btr_no_parent(struct btr_node *btrn);
 size_t btr_next_buffer(struct btr_node *btrn, char **bufp);
+size_t btr_next_buffer_omit(struct btr_node *btrn, size_t omit, char **bufp);
 void btr_consume(struct btr_node *btrn, size_t numbytes);
 int btr_exec_up(struct btr_node *btrn, const char *command, char **value_result);
 void btr_splice_out_node(struct btr_node *btrn);