Make marker searches utilize read buffer
This turns the search into a near perfect opportunity for memchr which
should be MUCH faster than calling the underlying reader's read method
for each single byte we want to inspect.
diff --git a/src/decoder.rs b/src/decoder.rs
index 8d918db..fede98e 100644
--- a/src/decoder.rs
+++ b/src/decoder.rs
@@ -6,7 +6,7 @@
parse_app, parse_com, parse_dht, parse_dqt, parse_dri, parse_sof, parse_sos, ScanInfo};
use upsampler::Upsampler;
use std::cmp;
-use std::io::Read;
+use std::io::{BufRead, BufReader, Read};
use std::mem;
use std::ops::Range;
use std::sync::Arc;
@@ -60,7 +60,7 @@
/// JPEG decoder
pub struct Decoder<R> {
- reader: R,
+ reader: BufReader<R>,
frame: Option<FrameInfo>,
dc_huffman_tables: Vec<Option<HuffmanTable>>,
@@ -82,7 +82,7 @@
/// Creates a new `Decoder` using the reader `reader`.
pub fn new(reader: R) -> Decoder<R> {
Decoder {
- reader: reader,
+ reader: BufReader::new(reader),
frame: None,
dc_huffman_tables: vec![None, None, None, None],
ac_huffman_tables: vec![None, None, None, None],
@@ -362,24 +362,42 @@
fn read_marker(&mut self) -> Result<Marker> {
loop {
+
// This should be an error as the JPEG spec doesn't allow extraneous data between marker segments.
// libjpeg allows this though and there are images in the wild utilising it, so we are
// forced to support this behavior.
// Sony Ericsson P990i is an example of a device which produce this sort of JPEGs.
- while self.reader.read_u8()? != 0xFF {}
+ loop {
+ let buf = self.reader.fill_buf()?;
+
+ if let Some(pos) = buf.iter().position(|&b| b == 0xFF) {
+ self.reader.consume(pos);
+ break;
+ }
+
+ // Woah, a full page of not-0xFF. Let's try the next page.
+ let consumed = buf.len();
+ self.reader.consume(consumed);
+ };
// Section B.1.1.2
// All markers are assigned two-byte codes: an X’FF’ byte followed by a
// byte which is not equal to 0 or X’FF’ (see Table B.1). Any marker may
// optionally be preceded by any number of fill bytes, which are bytes
// assigned code X’FF’.
- let mut byte = self.reader.read_u8()?;
+ // So, let's find the byte after 0xFF.
+ let byte = loop {
+ let buf = self.reader.fill_buf()?;
- // Section B.1.1.2
- // "Any marker may optionally be preceded by any number of fill bytes, which are bytes assigned code X’FF’."
- while byte == 0xFF {
- byte = self.reader.read_u8()?;
- }
+ if let Some(pos) = buf.iter().position(|&b| b != 0xFF) {
+ let byte = buf[pos];
+ self.reader.consume(pos + 1);
+ break byte;
+ }
+
+ let consumed = buf.len();
+ self.reader.consume(consumed);
+ };
if byte != 0x00 && byte != 0xFF {
return Ok(Marker::from_u8(byte).unwrap());
