hare

commit 4564f6bf19ccc41c297dc98c9e96cb09f71b85f8
parent 3ac9c5240b17d094b139c2a79f0ac67f0a965ebb
Author: Lassi Pulkkinen <lassi@pulk.fi>
Date:   Mon, 27 Feb 2023 02:57:17 +0200

bufio: Fix excessive memmoves in buffered_read

The buffer contents are now only moved to index 0 whenever new data is
to be read from the underlying reader. The start of buffered data is
tracked by the new rpos field.

Some room for improvement remains (ring buffer, maybe?), but at least it
performs better than no buffering...

Signed-off-by: Lassi Pulkkinen <lassi@pulk.fi>

Diffstat:
M
bufio/buffered.ha
 | 
27
++++++++++++++-------------

1 file changed, 14 insertions(+), 13 deletions(-)
diff --git a/bufio/buffered.ha b/bufio/buffered.ha
@@ -33,6 +33,7 @@ export type bufstream = struct {
 	source: io::handle,
 	rbuffer: []u8,
 	wbuffer: []u8,
+	rpos: size,
 	ravail: size,
 	wavail: size,
 	flush: []u8,
@@ -79,6 +80,7 @@ export fn buffered(
 		rbuffer = rbuf,
 		wbuffer = wbuf,
 		flush = flush_default,
+		rpos = len(rbuf), // necessary for unread() before read()
 		...
 	};
 };
@@ -135,10 +137,10 @@ export fn unread(s: io::handle, buf: []u8) void = {
 	case =>
 		abort("Attempted unread on unbuffered stream");
 	};
-	assert(len(s.rbuffer) - s.ravail >= len(buf),
+	assert(s.rpos >= len(buf),
 		"Attempted to unread more data than buffer has available");
-	let sl = s.rbuffer[..s.ravail];
-	static insert(sl[0], buf...);
+	s.rbuffer[s.rpos - len(buf)..s.rpos] = buf;
+	s.rpos -= len(buf);
 	s.ravail += len(buf);
 };
 
@@ -168,26 +170,25 @@ fn buffered_close_static(s: *io::stream) (void | io::error) = {
 fn buffered_read(s: *io::stream, buf: []u8) (size | io::EOF | io::error) = {
 	assert(s.reader == &buffered_read);
 	let s = s: *bufstream;
-	let n = if (len(buf) < len(s.rbuffer)) len(buf) else len(s.rbuffer);
-	if (n > s.ravail) {
-		let z = match (io::read(s.source, s.rbuffer[s.ravail..])) {
+
+	if (s.ravail < len(buf) && s.ravail < len(s.rbuffer)) {
+		s.rbuffer[..s.ravail] = s.rbuffer[s.rpos..s.rpos + s.ravail];
+		s.rpos = 0;
+		match (io::read(s.source, s.rbuffer[s.ravail..])) {
 		case let err: io::error =>
 			return err;
 		case io::EOF =>
 			if (s.ravail == 0) {
 				return io::EOF;
 			};
-			yield 0z;
 		case let z: size =>
-			yield z;
+			s.ravail += z;
 		};
-		s.ravail += z;
-		n = if (n > s.ravail) s.ravail else n;
-		assert(n != 0);
 	};
 
-	buf[..n] = s.rbuffer[..n];
-	s.rbuffer[..len(s.rbuffer) - n] = s.rbuffer[n..];
+	const n = if (len(buf) < s.ravail) len(buf) else s.ravail;
+	buf[..n] = s.rbuffer[s.rpos..s.rpos + n];
+	s.rpos += n;
 	s.ravail -= n;
 	return n;
 };