[0.98.4] add jack_ringbuffer_peek()

git-svn-id: svn+ssh://jackaudio.org/trunk/jack@729 0c269be4-1314-0410-8aa9-9f06e86f4224

configure.in

@@ -15,7 +15,7 @@ dnl                 changes are made
 dnl ---
 JACK_MAJOR_VERSION=0
 JACK_MINOR_VERSION=98
-JACK_MICRO_VERSION=3
+JACK_MICRO_VERSION=4
 
 dnl ---
 dnl HOWTO: updating the jack protocol version

jack/ringbuffer.h

@@ -137,6 +137,23 @@ void jack_ringbuffer_get_write_vector(const jack_ringbuffer_t *rb,
  */
 size_t jack_ringbuffer_read(jack_ringbuffer_t *rb, char *dest, size_t cnt);
 
+/**
+ * Read data from the ringbuffer. Opposed to jack_ringbuffer_read()
+ * this function does not move the read pointer. Thus it's
+ * a convenient way to inspect data in the ringbuffer in a
+ * continous fashion. The price is that the data is copied
+ * into a user provided buffer. For "raw" non-copy inspection
+ * of the data in the ringbuffer use jack_ringbuffer_get_read_vector().
+ *
+ * @param rb a pointer to the ringbuffer structure.
+ * @param dest a pointer to a buffer where data read from the
+ * ringbuffer will go.
+ * @param cnt the number of bytes to read.
+ *
+ * @return the number of bytes read, which may range from 0 to cnt.
+ */
+size_t jack_ringbuffer_peek(jack_ringbuffer_t *rb, char *dest, size_t cnt);
+
 /**
  * Advance the read pointer.
  *

libjack/ringbuffer.c

@@ -170,6 +170,51 @@ jack_ringbuffer_read (jack_ringbuffer_t * rb, char *dest, size_t cnt)
   return to_read;
 }
 
+/* The copying data reader w/o read pointer advance.  Copy at most 
+   `cnt' bytes from `rb' to `dest'.  Returns the actual number of bytes 
+copied. */
+
+size_t
+jack_ringbuffer_peek (jack_ringbuffer_t * rb, char *dest, size_t cnt)
+{
+  size_t free_cnt;
+  size_t cnt2;
+  size_t to_read;
+  size_t n1, n2;
+  size_t tmp_read_ptr;
+
+  tmp_read_ptr = rb->read_ptr;
+
+  if ((free_cnt = jack_ringbuffer_read_space (rb)) == 0) {
+    return 0;
+  }
+
+  to_read = cnt > free_cnt ? free_cnt : cnt;
+
+  cnt2 = tmp_read_ptr + to_read;
+
+  if (cnt2 > rb->size) {
+    n1 = rb->size - tmp_read_ptr;
+    n2 = cnt2 & rb->size_mask;
+  } else {
+    n1 = to_read;
+    n2 = 0;
+  }
+
+  memcpy (dest, &(rb->buf[tmp_read_ptr]), n1);
+  tmp_read_ptr += n1;
+  tmp_read_ptr &= rb->size_mask;
+
+  if (n2) {
+    memcpy (dest + n1, &(rb->buf[tmp_read_ptr]), n2);
+    tmp_read_ptr += n2;
+    tmp_read_ptr &= rb->size_mask;
+  }
+
+  return to_read;
+}
+
+
 /* The copying data writer.  Copy at most `cnt' bytes to `rb' from
    `src'.  Returns the actual number of bytes copied. */