Merging upstream version 1.71.1+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 107 insertions, 0 deletions

diff --git a/vendor/ruzstd/src/decoding/bit_reader.rs b/vendor/ruzstd/src/decoding/bit_reader.rs
new file mode 100644
index 000000000..e07ac45c4
--- /dev/null
+++ b/vendor/ruzstd/src/decoding/bit_reader.rs
@@ -0,0 +1,107 @@
+pub struct BitReader<'s> {
+    idx: usize, //index counts bits already read
+    source: &'s [u8],
+}
+
+#[derive(Debug, thiserror::Error)]
+#[non_exhaustive]
+pub enum GetBitsError {
+    #[error("Cant serve this request. The reader is limited to {limit} bits, requested {num_requested_bits} bits")]
+    TooManyBits {
+        num_requested_bits: usize,
+        limit: u8,
+    },
+    #[error("Can't read {requested} bits, only have {remaining} bits left")]
+    NotEnoughRemainingBits { requested: usize, remaining: usize },
+}
+
+impl<'s> BitReader<'s> {
+    pub fn new(source: &'s [u8]) -> BitReader<'_> {
+        BitReader { idx: 0, source }
+    }
+
+    pub fn bits_left(&self) -> usize {
+        self.source.len() * 8 - self.idx
+    }
+
+    pub fn bits_read(&self) -> usize {
+        self.idx
+    }
+
+    pub fn return_bits(&mut self, n: usize) {
+        if n > self.idx {
+            panic!("Cant return this many bits");
+        }
+        self.idx -= n;
+    }
+
+    pub fn get_bits(&mut self, n: usize) -> Result<u64, GetBitsError> {
+        if n > 64 {
+            return Err(GetBitsError::TooManyBits {
+                num_requested_bits: n,
+                limit: 64,
+            });
+        }
+        if self.bits_left() < n {
+            return Err(GetBitsError::NotEnoughRemainingBits {
+                requested: n,
+                remaining: self.bits_left(),
+            });
+        }
+
+        let old_idx = self.idx;
+
+        let bits_left_in_current_byte = 8 - (self.idx % 8);
+        let bits_not_needed_in_current_byte = 8 - bits_left_in_current_byte;
+
+        //collect bits from the currently pointed to byte
+        let mut value = u64::from(self.source[self.idx / 8] >> bits_not_needed_in_current_byte);
+
+        if bits_left_in_current_byte >= n {
+            //no need for fancy stuff
+
+            //just mask all but the needed n bit
+            value &= (1 << n) - 1;
+            self.idx += n;
+        } else {
+            self.idx += bits_left_in_current_byte;
+
+            //n spans over multiple bytes
+            let full_bytes_needed = (n - bits_left_in_current_byte) / 8;
+            let bits_in_last_byte_needed = n - bits_left_in_current_byte - full_bytes_needed * 8;
+
+            assert!(
+                bits_left_in_current_byte + full_bytes_needed * 8 + bits_in_last_byte_needed == n
+            );
+
+            let mut bit_shift = bits_left_in_current_byte; //this many bits are already set in value
+
+            assert!(self.idx % 8 == 0);
+
+            //collect full bytes
+            for _ in 0..full_bytes_needed {
+                value |= u64::from(self.source[self.idx / 8]) << bit_shift;
+                self.idx += 8;
+                bit_shift += 8;
+            }
+
+            assert!(n - bit_shift == bits_in_last_byte_needed);
+
+            if bits_in_last_byte_needed > 0 {
+                let val_las_byte =
+                    u64::from(self.source[self.idx / 8]) & ((1 << bits_in_last_byte_needed) - 1);
+                value |= val_las_byte << bit_shift;
+                self.idx += bits_in_last_byte_needed;
+            }
+        }
+
+        assert!(self.idx == old_idx + n);
+
+        Ok(value)
+    }
+
+    pub fn reset(&mut self, new_source: &'s [u8]) {
+        self.idx = 0;
+        self.source = new_source;
+    }
+}