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Make varint sizing logic use smallest working size;

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fix bad constant/test.
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Tangent 128 2017-07-07 02:27:13 -04:00
parent 6c99eca673
commit b1b157c6be
1 changed files with 20 additions and 7 deletions
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27
src/ebml.rs
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@ -110,9 +110,6 @@ pub fn decode_uint(bytes: &[u8]) -> Result<u64, Error> {
} }
const SMALL_FLAG: u64 = 0x80; const SMALL_FLAG: u64 = 0x80;
const SMALL_MAX: u64 = SMALL_FLAG - 2;
const TWO_FLAG: u64 = 0x60 << (8*1);
const TWO_MAX: u64 = TWO_FLAG - 2;
const EIGHT_FLAG: u64 = 0x01 << (8*7); const EIGHT_FLAG: u64 = 0x01 << (8*7);
const EIGHT_MAX: u64 = EIGHT_FLAG - 2; const EIGHT_MAX: u64 = EIGHT_FLAG - 2;
@ -123,9 +120,19 @@ pub fn encode_varint(varint: Varint, buffer: &mut [u8]) -> Result<usize, WriteEr
Varint::Value(too_big) if too_big >= EIGHT_MAX => { Varint::Value(too_big) if too_big >= EIGHT_MAX => {
return Err(WriteError::OutOfRange) return Err(WriteError::OutOfRange)
}, },
Varint::Value(small @ 0 ... SMALL_MAX) => (1, small | SMALL_FLAG), Varint::Value(value) => {
Varint::Value(two @ 0x7F ... TWO_MAX) => (2, two | TWO_FLAG), let mut flag = SMALL_FLAG;
Varint::Value(eight) => (8, eight | EIGHT_FLAG), let mut size = 1;
// flag bit - 1 = UNKNOWN representation once OR'd with the flag;
// if we're less than that, we can OR with the flag bit to get a valid Varint
while value >= (flag - 1) {
// right shift length bit by 1 to indicate adding a new byte;
// left shift by 8 because there's a new byte at the end
flag = flag << (8 - 1);
size += 1;
};
(size, flag | value)
}
}; };
if buffer.len() < size { if buffer.len() < size {
@ -214,6 +221,7 @@ mod tests {
let mut buffer = [0; 10]; let mut buffer = [0; 10];
let mut no_space = [0; 0]; let mut no_space = [0; 0];
// 1 byte
assert_eq!(encode_varint(Varint::Unknown, &mut buffer), Ok(1)); assert_eq!(encode_varint(Varint::Unknown, &mut buffer), Ok(1));
assert_eq!(buffer[0], 0xFF); assert_eq!(buffer[0], 0xFF);
assert_eq!(encode_varint(Varint::Unknown, &mut no_space), Err(WriteError::BufferTooSmall)); assert_eq!(encode_varint(Varint::Unknown, &mut no_space), Err(WriteError::BufferTooSmall));
@ -230,9 +238,14 @@ mod tests {
assert_eq!(buffer[0], 0xF0 | 126); assert_eq!(buffer[0], 0xF0 | 126);
assert_eq!(encode_varint(Varint::Value(126), &mut no_space), Err(WriteError::BufferTooSmall)); assert_eq!(encode_varint(Varint::Value(126), &mut no_space), Err(WriteError::BufferTooSmall));
// 2 bytes
assert_eq!(encode_varint(Varint::Value(127), &mut buffer), Ok(2)); assert_eq!(encode_varint(Varint::Value(127), &mut buffer), Ok(2));
assert_eq!(&buffer[0..2], &[0x60, 127]); assert_eq!(&buffer[0..2], &[0x40, 127]);
assert_eq!(encode_varint(Varint::Value(127), &mut no_space), Err(WriteError::BufferTooSmall)); assert_eq!(encode_varint(Varint::Value(127), &mut no_space), Err(WriteError::BufferTooSmall));
assert_eq!(encode_varint(Varint::Value(128), &mut buffer), Ok(2));
assert_eq!(&buffer[0..2], &[0x40, 128]);
assert_eq!(encode_varint(Varint::Value(128), &mut no_space), Err(WriteError::BufferTooSmall));
} }
#[test] #[test]