From b1c2d7ac7c100653e6e1056cd9b1f7ffe5cc34d9 Mon Sep 17 00:00:00 2001
From: polyphemus <rolfmorel@gmail.com>
Date: Tue, 17 Jun 2014 14:22:44 +0200
Subject: [PATCH] Rewrite cut_bytes()

Do no longer iterate over each byte and instead rely on the Buffer trait
to find the newline for us. Iterate over the ranges to specify slices of
the line which need to be printed out.

This rewrite gives a signifcant performance increase:
Old:    1.32s
mahkoh: 0.90s
New:    0.20s
GNU:    0.15s
---
 cut/cut.rs | 64 ++++++++++++++++++++++++------------------------------
 1 file changed, 28 insertions(+), 36 deletions(-)

diff --git a/cut/cut.rs b/cut/cut.rs
index deedda907..1d3156913 100644
--- a/cut/cut.rs
+++ b/cut/cut.rs
@@ -71,50 +71,42 @@ fn cut_bytes<T: Reader>(mut reader: BufferedReader<T>,
         None => (false, "".to_str())
     };
 
-    let mut byte_pos = 0;
-    let mut print_delim = false;
-    let mut range_pos = 0;
-
-    loop {
-        let mut byte = [0u8];
-        match reader.read(byte) {
-            Ok(1) => (),
-            Err(std::io::IoError{ kind: std::io::EndOfFile, ..}) => {
-                if byte_pos > 0 {
-                    out.write_u8('\n' as u8).unwrap();
-                }
-                break
-            }
+    'newline: loop {
+        let line = match reader.read_until(b'\n') {
+            Ok(line) => line,
+            Err(std::io::IoError{ kind: std::io::EndOfFile, ..}) => break,
             _ => fail!(),
-        }
-        let byte = byte[0];
+        };
 
-        if byte == ('\n' as u8) {
-            out.write_u8('\n' as u8).unwrap();
-            byte_pos = 0;
-            print_delim = false;
-            range_pos = 0;
-        } else {
-            byte_pos += 1;
+        let line_len = line.len();
+        let mut print_delim = false;
 
-            if byte_pos > ranges.get(range_pos).high {
-                range_pos += 1;
-            }
+        for &Range{ low: low, high: high } in ranges.iter() {
+            if low > line_len { break; }
 
-            let cur_range = *ranges.get(range_pos);
-
-            if byte_pos >= cur_range.low {
-                if use_delim {
-                    if print_delim && byte_pos == cur_range.low {
-                        out.write_str(out_delim.as_slice()).unwrap();
-                    }
-
-                    print_delim = true;
+            if use_delim {
+                if print_delim {
+                    out.write_str(out_delim.as_slice());
                 }
+                print_delim = true;
+            }
 
-                out.write_u8(byte).unwrap();
+            if high >= line_len {
+                let segment = line.slice(low - 1, line_len);
+
+                out.write(segment);
+
+                if *line.get(line_len - 1) == b'\n' {
+                    continue 'newline
+                }
+            } else {
+                let segment = line.slice(low - 1, high);
+
+                out.write(segment);
             }
         }
+
+        out.write(&[b'\n']);
     }
 
     0