vendor/chrono/src/format/scan.rs - toolchain/rustc - Git at Google

 // This is a part of Chrono.
 // See README.md and LICENSE.txt for details.

 /*!
  * Various scanning routines for the parser.
  */

 #![allow(deprecated)]

 use super::{ParseResult, INVALID, OUT_OF_RANGE, TOO_SHORT};
 use Weekday;

 /// Returns true when two slices are equal case-insensitively (in ASCII).
 /// Assumes that the `pattern` is already converted to lower case.
 fn equals(s: &str, pattern: &str) -> bool {
     let mut xs = s.as_bytes().iter().map(|&c| match c {
         b'A'...b'Z' => c + 32,
         _ => c,
     });
     let mut ys = pattern.as_bytes().iter().cloned();
     loop {
         match (xs.next(), ys.next()) {
             (None, None) => return true,
             (None, _) | (_, None) => return false,
             (Some(x), Some(y)) if x != y => return false,
             _ => (),
         }
     }
 }

 /// Tries to parse the non-negative number from `min` to `max` digits.
 ///
 /// The absence of digits at all is an unconditional error.
 /// More than `max` digits are consumed up to the first `max` digits.
 /// Any number that does not fit in `i64` is an error.
 #[inline]
 pub fn number(s: &str, min: usize, max: usize) -> ParseResult<(&str, i64)> {
     assert!(min <= max);

     // We are only interested in ascii numbers, so we can work with the `str` as bytes. We stop on
     // the first non-numeric byte, which may be another ascii character or beginning of multi-byte
     // UTF-8 character.
     let bytes = s.as_bytes();
     if bytes.len() < min {
         return Err(TOO_SHORT);
     }

     let mut n = 0i64;
     for (i, c) in bytes.iter().take(max).cloned().enumerate() {
         // cloned() = copied()
         if c < b'0' || b'9' < c {
             if i < min {
                 return Err(INVALID);
             } else {
                 return Ok((&s[i..], n));
             }
         }

         n = match n.checked_mul(10).and_then(|n| n.checked_add((c - b'0') as i64)) {
             Some(n) => n,
             None => return Err(OUT_OF_RANGE),
         };
     }

     Ok((&s[::core::cmp::min(max, bytes.len())..], n))
 }

 /// Tries to consume at least one digits as a fractional second.
 /// Returns the number of whole nanoseconds (0--999,999,999).
 pub fn nanosecond(s: &str) -> ParseResult<(&str, i64)> {
     // record the number of digits consumed for later scaling.
     let origlen = s.len();
     let (s, v) = number(s, 1, 9)?;
     let consumed = origlen - s.len();

     // scale the number accordingly.
     static SCALE: [i64; 10] =
         [0, 100_000_000, 10_000_000, 1_000_000, 100_000, 10_000, 1_000, 100, 10, 1];
     let v = v.checked_mul(SCALE[consumed]).ok_or(OUT_OF_RANGE)?;

     // if there are more than 9 digits, skip next digits.
     let s = s.trim_left_matches(|c: char| '0' <= c && c <= '9');

     Ok((s, v))
 }

 /// Tries to consume a fixed number of digits as a fractional second.
 /// Returns the number of whole nanoseconds (0--999,999,999).
 pub fn nanosecond_fixed(s: &str, digits: usize) -> ParseResult<(&str, i64)> {
     // record the number of digits consumed for later scaling.
     let (s, v) = number(s, digits, digits)?;

     // scale the number accordingly.
     static SCALE: [i64; 10] =
         [0, 100_000_000, 10_000_000, 1_000_000, 100_000, 10_000, 1_000, 100, 10, 1];
     let v = v.checked_mul(SCALE[digits]).ok_or(OUT_OF_RANGE)?;

     Ok((s, v))
 }

 /// Tries to parse the month index (0 through 11) with the first three ASCII letters.
 pub fn short_month0(s: &str) -> ParseResult<(&str, u8)> {
     if s.len() < 3 {
         return Err(TOO_SHORT);
     }
     let buf = s.as_bytes();
     let month0 = match (buf[0] | 32, buf[1] | 32, buf[2] | 32) {
         (b'j', b'a', b'n') => 0,
         (b'f', b'e', b'b') => 1,
         (b'm', b'a', b'r') => 2,
         (b'a', b'p', b'r') => 3,
         (b'm', b'a', b'y') => 4,
         (b'j', b'u', b'n') => 5,
         (b'j', b'u', b'l') => 6,
         (b'a', b'u', b'g') => 7,
         (b's', b'e', b'p') => 8,
         (b'o', b'c', b't') => 9,
         (b'n', b'o', b'v') => 10,
         (b'd', b'e', b'c') => 11,
         _ => return Err(INVALID),
     };
     Ok((&s[3..], month0))
 }

 /// Tries to parse the weekday with the first three ASCII letters.
 pub fn short_weekday(s: &str) -> ParseResult<(&str, Weekday)> {
     if s.len() < 3 {
         return Err(TOO_SHORT);
     }
     let buf = s.as_bytes();
     let weekday = match (buf[0] | 32, buf[1] | 32, buf[2] | 32) {
         (b'm', b'o', b'n') => Weekday::Mon,
         (b't', b'u', b'e') => Weekday::Tue,
         (b'w', b'e', b'd') => Weekday::Wed,
         (b't', b'h', b'u') => Weekday::Thu,
         (b'f', b'r', b'i') => Weekday::Fri,
         (b's', b'a', b't') => Weekday::Sat,
         (b's', b'u', b'n') => Weekday::Sun,
         _ => return Err(INVALID),
     };
     Ok((&s[3..], weekday))
 }

 /// Tries to parse the month index (0 through 11) with short or long month names.
 /// It prefers long month names to short month names when both are possible.
 pub fn short_or_long_month0(s: &str) -> ParseResult<(&str, u8)> {
     // lowercased month names, minus first three chars
     static LONG_MONTH_SUFFIXES: [&'static str; 12] =
         ["uary", "ruary", "ch", "il", "", "e", "y", "ust", "tember", "ober", "ember", "ember"];

     let (mut s, month0) = short_month0(s)?;

     // tries to consume the suffix if possible
     let suffix = LONG_MONTH_SUFFIXES[month0 as usize];
     if s.len() >= suffix.len() && equals(&s[..suffix.len()], suffix) {
         s = &s[suffix.len()..];
     }

     Ok((s, month0))
 }

 /// Tries to parse the weekday with short or long weekday names.
 /// It prefers long weekday names to short weekday names when both are possible.
 pub fn short_or_long_weekday(s: &str) -> ParseResult<(&str, Weekday)> {
     // lowercased weekday names, minus first three chars
     static LONG_WEEKDAY_SUFFIXES: [&'static str; 7] =
         ["day", "sday", "nesday", "rsday", "day", "urday", "day"];

     let (mut s, weekday) = short_weekday(s)?;

     // tries to consume the suffix if possible
     let suffix = LONG_WEEKDAY_SUFFIXES[weekday.num_days_from_monday() as usize];
     if s.len() >= suffix.len() && equals(&s[..suffix.len()], suffix) {
         s = &s[suffix.len()..];
     }

     Ok((s, weekday))
 }

 /// Tries to consume exactly one given character.
 pub fn char(s: &str, c1: u8) -> ParseResult<&str> {
     match s.as_bytes().first() {
         Some(&c) if c == c1 => Ok(&s[1..]),
         Some(_) => Err(INVALID),
         None => Err(TOO_SHORT),
     }
 }

 /// Tries to consume one or more whitespace.
 pub fn space(s: &str) -> ParseResult<&str> {
     let s_ = s.trim_left();
     if s_.len() < s.len() {
         Ok(s_)
     } else if s.is_empty() {
         Err(TOO_SHORT)
     } else {
         Err(INVALID)
     }
 }

 /// Consumes any number (including zero) of colon or spaces.
 pub fn colon_or_space(s: &str) -> ParseResult<&str> {
     Ok(s.trim_left_matches(|c: char| c == ':' || c.is_whitespace()))
 }

 /// Tries to parse `[-+]\d\d` continued by `\d\d`. Return an offset in seconds if possible.
 ///
 /// The additional `colon` may be used to parse a mandatory or optional `:`
 /// between hours and minutes, and should return either a new suffix or `Err` when parsing fails.
 pub fn timezone_offset<F>(s: &str, consume_colon: F) -> ParseResult<(&str, i32)>
 where
     F: FnMut(&str) -> ParseResult<&str>,
 {
     timezone_offset_internal(s, consume_colon, false)
 }

 fn timezone_offset_internal<F>(
     mut s: &str,
     mut consume_colon: F,
     allow_missing_minutes: bool,
 ) -> ParseResult<(&str, i32)>
 where
     F: FnMut(&str) -> ParseResult<&str>,
 {
     fn digits(s: &str) -> ParseResult<(u8, u8)> {
         let b = s.as_bytes();
         if b.len() < 2 {
             Err(TOO_SHORT)
         } else {
             Ok((b[0], b[1]))
         }
     }
     let negative = match s.as_bytes().first() {
         Some(&b'+') => false,
         Some(&b'-') => true,
         Some(_) => return Err(INVALID),
         None => return Err(TOO_SHORT),
     };
     s = &s[1..];

     // hours (00--99)
     let hours = match digits(s)? {
         (h1 @ b'0'...b'9', h2 @ b'0'...b'9') => i32::from((h1 - b'0') * 10 + (h2 - b'0')),
         _ => return Err(INVALID),
     };
     s = &s[2..];

     // colons (and possibly other separators)
     s = consume_colon(s)?;

     // minutes (00--59)
     // if the next two items are digits then we have to add minutes
     let minutes = if let Ok(ds) = digits(s) {
         match ds {
             (m1 @ b'0'...b'5', m2 @ b'0'...b'9') => i32::from((m1 - b'0') * 10 + (m2 - b'0')),
             (b'6'...b'9', b'0'...b'9') => return Err(OUT_OF_RANGE),
             _ => return Err(INVALID),
         }
     } else if allow_missing_minutes {
         0
     } else {
         return Err(TOO_SHORT);
     };
     s = match s.len() {
         len if len >= 2 => &s[2..],
         len if len == 0 => s,
         _ => return Err(TOO_SHORT),
     };

     let seconds = hours * 3600 + minutes * 60;
     Ok((s, if negative { -seconds } else { seconds }))
 }

 /// Same as `timezone_offset` but also allows for `z`/`Z` which is the same as `+00:00`.
 pub fn timezone_offset_zulu<F>(s: &str, colon: F) -> ParseResult<(&str, i32)>
 where
     F: FnMut(&str) -> ParseResult<&str>,
 {
     let bytes = s.as_bytes();
     match bytes.first() {
         Some(&b'z') | Some(&b'Z') => Ok((&s[1..], 0)),
         Some(&b'u') | Some(&b'U') => {
             if bytes.len() >= 3 {
                 let (b, c) = (bytes[1], bytes[2]);
                 match (b | 32, c | 32) {
                     (b't', b'c') => Ok((&s[3..], 0)),
                     _ => Err(INVALID),
                 }
             } else {
                 Err(INVALID)
             }
         }
         _ => timezone_offset(s, colon),
     }
 }

 /// Same as `timezone_offset` but also allows for `z`/`Z` which is the same as
 /// `+00:00`, and allows missing minutes entirely.
 pub fn timezone_offset_permissive<F>(s: &str, colon: F) -> ParseResult<(&str, i32)>
 where
     F: FnMut(&str) -> ParseResult<&str>,
 {
     match s.as_bytes().first() {
         Some(&b'z') | Some(&b'Z') => Ok((&s[1..], 0)),
         _ => timezone_offset_internal(s, colon, true),
     }
 }

 /// Same as `timezone_offset` but also allows for RFC 2822 legacy timezones.
 /// May return `None` which indicates an insufficient offset data (i.e. `-0000`).
 pub fn timezone_offset_2822(s: &str) -> ParseResult<(&str, Option<i32>)> {
     // tries to parse legacy time zone names
     let upto = s
         .as_bytes()
         .iter()
         .position(|&c| match c {
             b'a'...b'z' | b'A'...b'Z' => false,
             _ => true,
         })
         .unwrap_or_else(|| s.len());
     if upto > 0 {
         let name = &s[..upto];
         let s = &s[upto..];
         let offset_hours = |o| Ok((s, Some(o * 3600)));
         if equals(name, "gmt") || equals(name, "ut") {
             offset_hours(0)
         } else if equals(name, "edt") {
             offset_hours(-4)
         } else if equals(name, "est") || equals(name, "cdt") {
             offset_hours(-5)
         } else if equals(name, "cst") || equals(name, "mdt") {
             offset_hours(-6)
         } else if equals(name, "mst") || equals(name, "pdt") {
             offset_hours(-7)
         } else if equals(name, "pst") {
             offset_hours(-8)
         } else {
             Ok((s, None)) // recommended by RFC 2822: consume but treat it as -0000
         }
     } else {
         let (s_, offset) = timezone_offset(s, |s| Ok(s))?;
         Ok((s_, Some(offset)))
     }
 }
	// This is a part of Chrono.
	// See README.md and LICENSE.txt for details.

	/*!
	* Various scanning routines for the parser.
	*/

	#![allow(deprecated)]

	use super::{ParseResult, INVALID, OUT_OF_RANGE, TOO_SHORT};
	use Weekday;

	/// Returns true when two slices are equal case-insensitively (in ASCII).
	/// Assumes that the `pattern` is already converted to lower case.
	fn equals(s: &str, pattern: &str) -> bool {
	let mut xs = s.as_bytes().iter().map(\|&c\| match c {
	b'A'...b'Z' => c + 32,
	_ => c,
	});
	let mut ys = pattern.as_bytes().iter().cloned();
	loop {
	match (xs.next(), ys.next()) {
	(None, None) => return true,
	(None, _) \| (_, None) => return false,
	(Some(x), Some(y)) if x != y => return false,
	_ => (),
	}
	}
	}

	/// Tries to parse the non-negative number from `min` to `max` digits.
	///
	/// The absence of digits at all is an unconditional error.
	/// More than `max` digits are consumed up to the first `max` digits.
	/// Any number that does not fit in `i64` is an error.
	#[inline]
	pub fn number(s: &str, min: usize, max: usize) -> ParseResult<(&str, i64)> {
	assert!(min <= max);

	// We are only interested in ascii numbers, so we can work with the `str` as bytes. We stop on
	// the first non-numeric byte, which may be another ascii character or beginning of multi-byte
	// UTF-8 character.
	let bytes = s.as_bytes();
	if bytes.len() < min {
	return Err(TOO_SHORT);
	}

	let mut n = 0i64;
	for (i, c) in bytes.iter().take(max).cloned().enumerate() {
	// cloned() = copied()
	if c < b'0' \|\| b'9' < c {
	if i < min {
	return Err(INVALID);
	} else {
	return Ok((&s[i..], n));
	}
	}

	n = match n.checked_mul(10).and_then(\|n\| n.checked_add((c - b'0') as i64)) {
	Some(n) => n,
	None => return Err(OUT_OF_RANGE),
	};
	}

	Ok((&s[::core::cmp::min(max, bytes.len())..], n))
	}

	/// Tries to consume at least one digits as a fractional second.
	/// Returns the number of whole nanoseconds (0--999,999,999).
	pub fn nanosecond(s: &str) -> ParseResult<(&str, i64)> {
	// record the number of digits consumed for later scaling.
	let origlen = s.len();
	let (s, v) = number(s, 1, 9)?;
	let consumed = origlen - s.len();

	// scale the number accordingly.
	static SCALE: [i64; 10] =
	[0, 100_000_000, 10_000_000, 1_000_000, 100_000, 10_000, 1_000, 100, 10, 1];
	let v = v.checked_mul(SCALE[consumed]).ok_or(OUT_OF_RANGE)?;

	// if there are more than 9 digits, skip next digits.
	let s = s.trim_left_matches(\|c: char\| '0' <= c && c <= '9');

	Ok((s, v))
	}

	/// Tries to consume a fixed number of digits as a fractional second.
	/// Returns the number of whole nanoseconds (0--999,999,999).
	pub fn nanosecond_fixed(s: &str, digits: usize) -> ParseResult<(&str, i64)> {
	// record the number of digits consumed for later scaling.
	let (s, v) = number(s, digits, digits)?;

	// scale the number accordingly.
	static SCALE: [i64; 10] =
	[0, 100_000_000, 10_000_000, 1_000_000, 100_000, 10_000, 1_000, 100, 10, 1];
	let v = v.checked_mul(SCALE[digits]).ok_or(OUT_OF_RANGE)?;

	Ok((s, v))
	}

	/// Tries to parse the month index (0 through 11) with the first three ASCII letters.
	pub fn short_month0(s: &str) -> ParseResult<(&str, u8)> {
	if s.len() < 3 {
	return Err(TOO_SHORT);
	}
	let buf = s.as_bytes();
	let month0 = match (buf[0] \| 32, buf[1] \| 32, buf[2] \| 32) {
	(b'j', b'a', b'n') => 0,
	(b'f', b'e', b'b') => 1,
	(b'm', b'a', b'r') => 2,
	(b'a', b'p', b'r') => 3,
	(b'm', b'a', b'y') => 4,
	(b'j', b'u', b'n') => 5,
	(b'j', b'u', b'l') => 6,
	(b'a', b'u', b'g') => 7,
	(b's', b'e', b'p') => 8,
	(b'o', b'c', b't') => 9,
	(b'n', b'o', b'v') => 10,
	(b'd', b'e', b'c') => 11,
	_ => return Err(INVALID),
	};
	Ok((&s[3..], month0))
	}

	/// Tries to parse the weekday with the first three ASCII letters.
	pub fn short_weekday(s: &str) -> ParseResult<(&str, Weekday)> {
	if s.len() < 3 {
	return Err(TOO_SHORT);
	}
	let buf = s.as_bytes();
	let weekday = match (buf[0] \| 32, buf[1] \| 32, buf[2] \| 32) {
	(b'm', b'o', b'n') => Weekday::Mon,
	(b't', b'u', b'e') => Weekday::Tue,
	(b'w', b'e', b'd') => Weekday::Wed,
	(b't', b'h', b'u') => Weekday::Thu,
	(b'f', b'r', b'i') => Weekday::Fri,
	(b's', b'a', b't') => Weekday::Sat,
	(b's', b'u', b'n') => Weekday::Sun,
	_ => return Err(INVALID),
	};
	Ok((&s[3..], weekday))
	}

	/// Tries to parse the month index (0 through 11) with short or long month names.
	/// It prefers long month names to short month names when both are possible.
	pub fn short_or_long_month0(s: &str) -> ParseResult<(&str, u8)> {
	// lowercased month names, minus first three chars
	static LONG_MONTH_SUFFIXES: [&'static str; 12] =
	["uary", "ruary", "ch", "il", "", "e", "y", "ust", "tember", "ober", "ember", "ember"];

	let (mut s, month0) = short_month0(s)?;

	// tries to consume the suffix if possible
	let suffix = LONG_MONTH_SUFFIXES[month0 as usize];
	if s.len() >= suffix.len() && equals(&s[..suffix.len()], suffix) {
	s = &s[suffix.len()..];
	}

	Ok((s, month0))
	}

	/// Tries to parse the weekday with short or long weekday names.
	/// It prefers long weekday names to short weekday names when both are possible.
	pub fn short_or_long_weekday(s: &str) -> ParseResult<(&str, Weekday)> {
	// lowercased weekday names, minus first three chars
	static LONG_WEEKDAY_SUFFIXES: [&'static str; 7] =
	["day", "sday", "nesday", "rsday", "day", "urday", "day"];

	let (mut s, weekday) = short_weekday(s)?;

	// tries to consume the suffix if possible
	let suffix = LONG_WEEKDAY_SUFFIXES[weekday.num_days_from_monday() as usize];
	if s.len() >= suffix.len() && equals(&s[..suffix.len()], suffix) {
	s = &s[suffix.len()..];
	}

	Ok((s, weekday))
	}

	/// Tries to consume exactly one given character.
	pub fn char(s: &str, c1: u8) -> ParseResult<&str> {
	match s.as_bytes().first() {
	Some(&c) if c == c1 => Ok(&s[1..]),
	Some(_) => Err(INVALID),
	None => Err(TOO_SHORT),
	}
	}

	/// Tries to consume one or more whitespace.
	pub fn space(s: &str) -> ParseResult<&str> {
	let s_ = s.trim_left();
	if s_.len() < s.len() {
	Ok(s_)
	} else if s.is_empty() {
	Err(TOO_SHORT)
	} else {
	Err(INVALID)
	}
	}

	/// Consumes any number (including zero) of colon or spaces.
	pub fn colon_or_space(s: &str) -> ParseResult<&str> {
	Ok(s.trim_left_matches(\|c: char\| c == ':' \|\| c.is_whitespace()))
	}

	/// Tries to parse `[-+]\d\d` continued by `\d\d`. Return an offset in seconds if possible.
	///
	/// The additional `colon` may be used to parse a mandatory or optional `:`
	/// between hours and minutes, and should return either a new suffix or `Err` when parsing fails.
	pub fn timezone_offset<F>(s: &str, consume_colon: F) -> ParseResult<(&str, i32)>
	where
	F: FnMut(&str) -> ParseResult<&str>,
	{
	timezone_offset_internal(s, consume_colon, false)
	}

	fn timezone_offset_internal<F>(
	mut s: &str,
	mut consume_colon: F,
	allow_missing_minutes: bool,
	) -> ParseResult<(&str, i32)>
	where
	F: FnMut(&str) -> ParseResult<&str>,
	{
	fn digits(s: &str) -> ParseResult<(u8, u8)> {
	let b = s.as_bytes();
	if b.len() < 2 {
	Err(TOO_SHORT)
	} else {
	Ok((b[0], b[1]))
	}
	}
	let negative = match s.as_bytes().first() {
	Some(&b'+') => false,
	Some(&b'-') => true,
	Some(_) => return Err(INVALID),
	None => return Err(TOO_SHORT),
	};
	s = &s[1..];

	// hours (00--99)
	let hours = match digits(s)? {
	(h1 @ b'0'...b'9', h2 @ b'0'...b'9') => i32::from((h1 - b'0') * 10 + (h2 - b'0')),
	_ => return Err(INVALID),
	};
	s = &s[2..];

	// colons (and possibly other separators)
	s = consume_colon(s)?;

	// minutes (00--59)
	// if the next two items are digits then we have to add minutes
	let minutes = if let Ok(ds) = digits(s) {
	match ds {
	(m1 @ b'0'...b'5', m2 @ b'0'...b'9') => i32::from((m1 - b'0') * 10 + (m2 - b'0')),
	(b'6'...b'9', b'0'...b'9') => return Err(OUT_OF_RANGE),
	_ => return Err(INVALID),
	}
	} else if allow_missing_minutes {
	0
	} else {
	return Err(TOO_SHORT);
	};
	s = match s.len() {
	len if len >= 2 => &s[2..],
	len if len == 0 => s,
	_ => return Err(TOO_SHORT),
	};

	let seconds = hours * 3600 + minutes * 60;
	Ok((s, if negative { -seconds } else { seconds }))
	}

	/// Same as `timezone_offset` but also allows for `z`/`Z` which is the same as `+00:00`.
	pub fn timezone_offset_zulu<F>(s: &str, colon: F) -> ParseResult<(&str, i32)>
	where
	F: FnMut(&str) -> ParseResult<&str>,
	{
	let bytes = s.as_bytes();
	match bytes.first() {
	Some(&b'z') \| Some(&b'Z') => Ok((&s[1..], 0)),
	Some(&b'u') \| Some(&b'U') => {
	if bytes.len() >= 3 {
	let (b, c) = (bytes[1], bytes[2]);
	match (b \| 32, c \| 32) {
	(b't', b'c') => Ok((&s[3..], 0)),
	_ => Err(INVALID),
	}
	} else {
	Err(INVALID)
	}
	}
	_ => timezone_offset(s, colon),
	}
	}

	/// Same as `timezone_offset` but also allows for `z`/`Z` which is the same as
	/// `+00:00`, and allows missing minutes entirely.
	pub fn timezone_offset_permissive<F>(s: &str, colon: F) -> ParseResult<(&str, i32)>
	where
	F: FnMut(&str) -> ParseResult<&str>,
	{
	match s.as_bytes().first() {
	Some(&b'z') \| Some(&b'Z') => Ok((&s[1..], 0)),
	_ => timezone_offset_internal(s, colon, true),
	}
	}

	/// Same as `timezone_offset` but also allows for RFC 2822 legacy timezones.
	/// May return `None` which indicates an insufficient offset data (i.e. `-0000`).
	pub fn timezone_offset_2822(s: &str) -> ParseResult<(&str, Option<i32>)> {
	// tries to parse legacy time zone names
	let upto = s
	.as_bytes()
	.iter()
	.position(\|&c\| match c {
	b'a'...b'z' \| b'A'...b'Z' => false,
	_ => true,
	})
	.unwrap_or_else(\|\| s.len());
	if upto > 0 {
	let name = &s[..upto];
	let s = &s[upto..];
	let offset_hours = \|o\| Ok((s, Some(o * 3600)));
	if equals(name, "gmt") \|\| equals(name, "ut") {
	offset_hours(0)
	} else if equals(name, "edt") {
	offset_hours(-4)
	} else if equals(name, "est") \|\| equals(name, "cdt") {
	offset_hours(-5)
	} else if equals(name, "cst") \|\| equals(name, "mdt") {
	offset_hours(-6)
	} else if equals(name, "mst") \|\| equals(name, "pdt") {
	offset_hours(-7)
	} else if equals(name, "pst") {
	offset_hours(-8)
	} else {
	Ok((s, None)) // recommended by RFC 2822: consume but treat it as -0000
	}
	} else {
	let (s_, offset) = timezone_offset(s, \|s\| Ok(s))?;
	Ok((s_, Some(offset)))
	}
	}