| //! Common utilities, for internal use only. |
| |
| use crate::ptr; |
| |
| /// Helper methods to process immutable bytes. |
| pub(crate) trait ByteSlice: AsRef<[u8]> { |
| unsafe fn first_unchecked(&self) -> u8 { |
| debug_assert!(!self.is_empty()); |
| // SAFETY: safe as long as self is not empty |
| unsafe { *self.as_ref().get_unchecked(0) } |
| } |
| |
| /// Get if the slice contains no elements. |
| fn is_empty(&self) -> bool { |
| self.as_ref().is_empty() |
| } |
| |
| /// Check if the slice at least `n` length. |
| fn check_len(&self, n: usize) -> bool { |
| n <= self.as_ref().len() |
| } |
| |
| /// Check if the first character in the slice is equal to c. |
| fn first_is(&self, c: u8) -> bool { |
| self.as_ref().first() == Some(&c) |
| } |
| |
| /// Check if the first character in the slice is equal to c1 or c2. |
| fn first_is2(&self, c1: u8, c2: u8) -> bool { |
| if let Some(&c) = self.as_ref().first() { c == c1 || c == c2 } else { false } |
| } |
| |
| /// Bounds-checked test if the first character in the slice is a digit. |
| fn first_isdigit(&self) -> bool { |
| if let Some(&c) = self.as_ref().first() { c.is_ascii_digit() } else { false } |
| } |
| |
| /// Check if self starts with u with a case-insensitive comparison. |
| fn starts_with_ignore_case(&self, u: &[u8]) -> bool { |
| debug_assert!(self.as_ref().len() >= u.len()); |
| let iter = self.as_ref().iter().zip(u.iter()); |
| let d = iter.fold(0, |i, (&x, &y)| i | (x ^ y)); |
| d == 0 || d == 32 |
| } |
| |
| /// Get the remaining slice after the first N elements. |
| fn advance(&self, n: usize) -> &[u8] { |
| &self.as_ref()[n..] |
| } |
| |
| /// Get the slice after skipping all leading characters equal c. |
| fn skip_chars(&self, c: u8) -> &[u8] { |
| let mut s = self.as_ref(); |
| while s.first_is(c) { |
| s = s.advance(1); |
| } |
| s |
| } |
| |
| /// Get the slice after skipping all leading characters equal c1 or c2. |
| fn skip_chars2(&self, c1: u8, c2: u8) -> &[u8] { |
| let mut s = self.as_ref(); |
| while s.first_is2(c1, c2) { |
| s = s.advance(1); |
| } |
| s |
| } |
| |
| /// Read 8 bytes as a 64-bit integer in little-endian order. |
| unsafe fn read_u64_unchecked(&self) -> u64 { |
| debug_assert!(self.check_len(8)); |
| let src = self.as_ref().as_ptr() as *const u64; |
| // SAFETY: safe as long as self is at least 8 bytes |
| u64::from_le(unsafe { ptr::read_unaligned(src) }) |
| } |
| |
| /// Try to read the next 8 bytes from the slice. |
| fn read_u64(&self) -> Option<u64> { |
| if self.check_len(8) { |
| // SAFETY: self must be at least 8 bytes. |
| Some(unsafe { self.read_u64_unchecked() }) |
| } else { |
| None |
| } |
| } |
| |
| /// Calculate the offset of slice from another. |
| fn offset_from(&self, other: &Self) -> isize { |
| other.as_ref().len() as isize - self.as_ref().len() as isize |
| } |
| } |
| |
| impl ByteSlice for [u8] {} |
| |
| /// Helper methods to process mutable bytes. |
| pub(crate) trait ByteSliceMut: AsMut<[u8]> { |
| /// Write a 64-bit integer as 8 bytes in little-endian order. |
| unsafe fn write_u64_unchecked(&mut self, value: u64) { |
| debug_assert!(self.as_mut().len() >= 8); |
| let dst = self.as_mut().as_mut_ptr() as *mut u64; |
| // NOTE: we must use `write_unaligned`, since dst is not |
| // guaranteed to be properly aligned. Miri will warn us |
| // if we use `write` instead of `write_unaligned`, as expected. |
| // SAFETY: safe as long as self is at least 8 bytes |
| unsafe { |
| ptr::write_unaligned(dst, u64::to_le(value)); |
| } |
| } |
| } |
| |
| impl ByteSliceMut for [u8] {} |
| |
| /// Bytes wrapper with specialized methods for ASCII characters. |
| #[derive(Debug, Clone, Copy, PartialEq, Eq)] |
| pub(crate) struct AsciiStr<'a> { |
| slc: &'a [u8], |
| } |
| |
| impl<'a> AsciiStr<'a> { |
| pub fn new(slc: &'a [u8]) -> Self { |
| Self { slc } |
| } |
| |
| /// Advance the view by n, advancing it in-place to (n..). |
| pub unsafe fn step_by(&mut self, n: usize) -> &mut Self { |
| // SAFETY: safe as long n is less than the buffer length |
| self.slc = unsafe { self.slc.get_unchecked(n..) }; |
| self |
| } |
| |
| /// Advance the view by n, advancing it in-place to (1..). |
| pub unsafe fn step(&mut self) -> &mut Self { |
| // SAFETY: safe as long as self is not empty |
| unsafe { self.step_by(1) } |
| } |
| |
| /// Iteratively parse and consume digits from bytes. |
| pub fn parse_digits(&mut self, mut func: impl FnMut(u8)) { |
| while let Some(&c) = self.as_ref().first() { |
| let c = c.wrapping_sub(b'0'); |
| if c < 10 { |
| func(c); |
| // SAFETY: self cannot be empty |
| unsafe { |
| self.step(); |
| } |
| } else { |
| break; |
| } |
| } |
| } |
| } |
| |
| impl<'a> AsRef<[u8]> for AsciiStr<'a> { |
| #[inline] |
| fn as_ref(&self) -> &[u8] { |
| self.slc |
| } |
| } |
| |
| impl<'a> ByteSlice for AsciiStr<'a> {} |
| |
| /// Determine if 8 bytes are all decimal digits. |
| /// This does not care about the order in which the bytes were loaded. |
| pub(crate) fn is_8digits(v: u64) -> bool { |
| let a = v.wrapping_add(0x4646_4646_4646_4646); |
| let b = v.wrapping_sub(0x3030_3030_3030_3030); |
| (a | b) & 0x8080_8080_8080_8080 == 0 |
| } |
| |
| /// Iteratively parse and consume digits from bytes. |
| pub(crate) fn parse_digits(s: &mut &[u8], mut f: impl FnMut(u8)) { |
| while let Some(&c) = s.get(0) { |
| let c = c.wrapping_sub(b'0'); |
| if c < 10 { |
| f(c); |
| *s = s.advance(1); |
| } else { |
| break; |
| } |
| } |
| } |
| |
| /// A custom 64-bit floating point type, representing `f * 2^e`. |
| /// e is biased, so it be directly shifted into the exponent bits. |
| #[derive(Debug, Copy, Clone, PartialEq, Eq, Default)] |
| pub struct BiasedFp { |
| /// The significant digits. |
| pub f: u64, |
| /// The biased, binary exponent. |
| pub e: i32, |
| } |
| |
| impl BiasedFp { |
| pub const fn zero_pow2(e: i32) -> Self { |
| Self { f: 0, e } |
| } |
| } |