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remove bounds check using unsafe

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Robin Appelman 2020-01-06 18:53:12 +01:00
commit 7250ce3ae8
1 changed files with 10 additions and 9 deletions
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19
src/buffer.rs
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@ -89,9 +89,16 @@ where
} }
fn read_usize_bytes(&self, byte_index: usize) -> [u8; USIZE_SIZE] { fn read_usize_bytes(&self, byte_index: usize) -> [u8; USIZE_SIZE] {
self.bytes[byte_index..byte_index + USIZE_SIZE] debug_assert!(byte_index + USIZE_SIZE < self.bytes.len());
.try_into() // this is safe because all calling paths check that byte_index is less than the unpadded
.unwrap() // length (because they check based on bit_len), so with padding byte_index + USIZE_SIZE is
// always within bounds
unsafe {
self.bytes
.get_unchecked(byte_index..byte_index + USIZE_SIZE)
.try_into()
.unwrap()
}
} }
/// note that only the bottom USIZE - 1 bytes are usable /// note that only the bottom USIZE - 1 bytes are usable
@ -237,9 +244,6 @@ where
} }
} }
/// Panics:
///
/// requires position + count to not go out of bounds of the buffer: ((position + count) / 8) <= self.bytes.len()
#[inline] #[inline]
fn read_fit_usize<T>(&self, position: usize, count: usize) -> T fn read_fit_usize<T>(&self, position: usize, count: usize) -> T
where where
@ -249,9 +253,6 @@ where
T::from_unchecked(raw) T::from_unchecked(raw)
} }
/// Panics:
///
/// requires position + count to not go out of bounds of the buffer: ((position + count) / 8) <= self.bytes.len()
fn read_no_fit_usize<T>(&self, position: usize, count: usize) -> T fn read_no_fit_usize<T>(&self, position: usize, count: usize) -> T
where where
T: PrimInt + BitOrAssign + IsSigned + UncheckedPrimitiveInt, T: PrimInt + BitOrAssign + IsSigned + UncheckedPrimitiveInt,