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Explain contract of {read, write}_target_uint

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Jubilee Young 2020-08-21 00:55:33 -07:00
parent fe2a867125
commit dc00efff9f
1 changed files with 6 additions and 0 deletions
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6
compiler/rustc_middle/src/mir/interpret/mod.rs
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@ -561,17 +561,23 @@ pub fn write_target_uint(
mut target: &mut [u8], mut target: &mut [u8],
data: u128, data: u128,
) -> Result<(), io::Error> { ) -> Result<(), io::Error> {
// This u128 holds an "any-size uint" (since smaller uints can fits in it)
// So we do not write all bytes of the u128, just the "payload".
match endianness { match endianness {
Endian::Little => target.write(&data.to_le_bytes())?, Endian::Little => target.write(&data.to_le_bytes())?,
Endian::Big => target.write(&data.to_be_bytes())?, Endian::Big => target.write(&data.to_be_bytes())?,
}; };
debug_assert!(target.len() == 0); // We should have filled the target buffer.
Ok(()) Ok(())
} }
#[inline] #[inline]
pub fn read_target_uint(endianness: Endian, mut source: &[u8]) -> Result<u128, io::Error> { pub fn read_target_uint(endianness: Endian, mut source: &[u8]) -> Result<u128, io::Error> {
// This u128 holds an "any-size uint" (since smaller uints can fits in it)
let mut buf = [0u8; std::mem::size_of::<u128>()]; let mut buf = [0u8; std::mem::size_of::<u128>()];
// So we do not read exactly 16 bytes into the u128, just the "payload".
source.read(&mut buf)?; source.read(&mut buf)?;
debug_assert!(source.len() == 0); // We should have consumed the source buffer.
match endianness { match endianness {
Endian::Little => Ok(u128::from_le_bytes(buf)), Endian::Little => Ok(u128::from_le_bytes(buf)),
Endian::Big => Ok(u128::from_be_bytes(buf)), Endian::Big => Ok(u128::from_be_bytes(buf)),