RGBCube/uutils-coreutils
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Rewrite cut_bytes()

Browse source 
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
This commit is contained in:
polyphemus 2014-06-17 14:22:44 +02:00
parent 8b1ff08bd5
commit b1c2d7ac7c
1 changed files with 28 additions and 36 deletions
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64
cut/cut.rs
View file

@ -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']);
}
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