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Code Issues Releases Wiki Activity

Clean up the API for reading bits

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This commit is contained in:
Bradlee Speice 2019-05-06 16:22:00 -04:00
parent 7eb92c77fb
commit 2b6e62dca1
1 changed files with 19 additions and 7 deletions
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26
src/lib.rs
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@ -11,6 +11,7 @@ pub enum KError<'a> {
Encoding { expected: &'static str }, Encoding { expected: &'static str },
MissingRoot, MissingRoot,
MissingParent, MissingParent,
ReadBitsTooLarge { requested: usize },
UnexpectedContents { actual: &'a [u8] }, UnexpectedContents { actual: &'a [u8] },
UnknownVariant(i64), UnknownVariant(i64),
} }
@ -76,7 +77,7 @@ pub trait KStream {
fn read_f8le(&self) -> KResult<f64>; fn read_f8le(&self) -> KResult<f64>;
fn align_to_byte(&self) -> KResult<()>; fn align_to_byte(&self) -> KResult<()>;
fn read_bits_int(&self, n: u32) -> KResult<u64>; fn read_bits_int(&self, n: usize) -> KResult<u64>;
fn read_bytes(&self, len: usize) -> KResult<&[u8]>; fn read_bytes(&self, len: usize) -> KResult<&[u8]>;
fn read_bytes_full(&self) -> KResult<&[u8]>; fn read_bytes_full(&self) -> KResult<&[u8]>;
@ -243,9 +244,13 @@ impl<'a> KStream for BytesReader<'a> {
Ok(()) Ok(())
} }
// TODO: Clean up the casting nightmare fn read_bits_int(&self, n: usize) -> KResult<u64> {
fn read_bits_int(&self, n: u32) -> KResult<u64> { if n > 64 {
let bits_needed = n as i64 - self.state.borrow().bits_left; return Err(KError::ReadBitsTooLarge { requested: n });
}
let n = n as i64;
let bits_needed = n - self.state.borrow().bits_left;
if bits_needed > 0 { if bits_needed > 0 {
// 1 bit => 1 byte // 1 bit => 1 byte
// 8 bits => 1 byte // 8 bits => 1 byte
@ -253,7 +258,6 @@ impl<'a> KStream for BytesReader<'a> {
let bytes_needed = ((bits_needed - 1) / 8) + 1; let bytes_needed = ((bits_needed - 1) / 8) + 1;
// Need to be careful here, because `read_bytes` will borrow our state as mutable, // Need to be careful here, because `read_bytes` will borrow our state as mutable,
// which panics if we're currently holding a borrow // which panics if we're currently holding a borrow
// TODO: Return error for bytes_needed > 8
let buf = self.read_bytes(bytes_needed as usize)?; let buf = self.read_bytes(bytes_needed as usize)?;
let mut inner = self.state.borrow_mut(); let mut inner = self.state.borrow_mut();
for b in buf { for b in buf {
@ -265,12 +269,12 @@ impl<'a> KStream for BytesReader<'a> {
let mut inner = self.state.borrow_mut(); let mut inner = self.state.borrow_mut();
let mut mask = (1u64 << n) - 1; let mut mask = (1u64 << n) - 1;
let shift_bits = inner.bits_left - n as i64; let shift_bits = inner.bits_left - n;
mask <<= shift_bits; mask <<= shift_bits;
let result: u64 = (inner.bits & mask) >> shift_bits; let result: u64 = (inner.bits & mask) >> shift_bits;
inner.bits_left -= n as i64; inner.bits_left -= n;
mask = (1u64 << inner.bits_left) - 1; mask = (1u64 << inner.bits_left) - 1;
inner.bits &= mask; inner.bits &= mask;
@ -364,4 +368,12 @@ mod tests {
assert_eq!(reader.read_bits_int(9).unwrap(), 3); assert_eq!(reader.read_bits_int(9).unwrap(), 3);
} }
#[test]
fn read_bits_too_large() {
let b: Vec<u8> = vec![1, 2, 3, 4, 5, 6, 7, 8, 9];
let mut reader = BytesReader::new(&b[..]);
assert_eq!(reader.read_bits_int(65).unwrap_err(), KError::ReadBitsTooLarge { requested: 65 })
}
} }