%PDF-
%PDF-
Mini Shell
Mini Shell
// re2rust $INPUT -o $OUTPUT
// Store u32 number in u64 during parsing to simplify overflow hadling.
struct State<'a> {
str: &'a [u8],
cur: usize,
mar: usize,
num: u64,
}
/*!re2c // Common re2c definitions shared between all functions.
re2c:yyfill:enable = 0;
re2c:define:YYCTYPE = u8;
re2c:define:YYPEEK = "*st.str.get_unchecked(st.cur)";
re2c:define:YYSKIP = "st.cur += 1;";
re2c:define:YYBACKUP = "st.mar = st.cur;";
re2c:define:YYRESTORE = "st.cur = st.mar;";
re2c:define:YYSHIFT = "st.cur = (st.cur as isize + @@) as usize;";
*/
const ERROR: u64 = std::u32::MAX as u64 + 1; // overflow
macro_rules! maybe { // Convert the number from u64 to optional u32.
($n:expr) => { if $n < ERROR { Some($n as u32) } else { None } }
}
// Add digit with the given base, checking for overflow.
fn add(st: &mut State, offs: u8, base: u64) {
let digit = unsafe { st.str.get_unchecked(st.cur - 1) } - offs;
st.num = std::cmp::min(st.num * base + digit as u64, ERROR);
}
fn parse_u32(s: & [u8]) -> Option<u32> {
let mut st = State {str: s, cur: 0, mar: 0, num: 0};
/*!re2c
'0b' / [01] { return parse_bin(&mut st); }
"0" { return parse_oct(&mut st); }
"" / [1-9] { return parse_dec(&mut st); }
'0x' / [0-9a-fA-F] { return parse_hex(&mut st); }
* { return None; }
*/
}
fn parse_bin(st: &mut State) -> Option<u32> {
'bin: loop {/*!re2c
[01] { add(st, 48, 2); continue 'bin; }
* { return maybe!(st.num); }
*/}
}
fn parse_oct(st: &mut State) -> Option<u32> {
'oct: loop {/*!re2c
[0-7] { add(st, 48, 8); continue 'oct; }
* { return maybe!(st.num); }
*/}
}
fn parse_dec(st: &mut State) -> Option<u32> {
'dec: loop {/*!re2c
[0-9] { add(st, 48, 10); continue 'dec; }
* { return maybe!(st.num); }
*/}
}
fn parse_hex(st: &mut State) -> Option<u32> {
'hex: loop {/*!re2c
[0-9] { add(st, 48, 16); continue 'hex; }
[a-f] { add(st, 87, 16); continue 'hex; }
[A-F] { add(st, 55, 16); continue 'hex; }
* { return maybe!(st.num); }
*/}
}
fn main() {
assert_eq!(parse_u32(b"\0"), None);
assert_eq!(parse_u32(b"1234567890\0"), Some(1234567890));
assert_eq!(parse_u32(b"0b1101\0"), Some(13));
assert_eq!(parse_u32(b"0x7Fe\0"), Some(2046));
assert_eq!(parse_u32(b"0644\0"), Some(420));
assert_eq!(parse_u32(b"9999999999\0"), None);
}
Zerion Mini Shell 1.0