[3/7][record] add packed data header

src/record/data_header.rs

@@ -0,0 +1,75 @@
+use super::{ALIGNMENT, HEADER_SIZE};
+
+#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
+#[repr(transparent)]
+pub(super) struct RecordDataHeader(u64);
+
+impl RecordDataHeader {
+    const KEY_INLINE_BIT: u64 = 1 << 0;
+    const VALUE_INLINE_BIT: u64 = 1 << 1;
+
+    const FILLER_WORDS_SHIFT: u32 = 6;
+    const KEY_LENGTH_SHIFT: u32 = 14;
+    const VALUE_LENGTH_SHIFT: u32 = 24;
+
+    const FILLER_WORDS_MASK: u64 = ((1_u64 << 8) - 1) << Self::FILLER_WORDS_SHIFT;
+    const KEY_LENGTH_MASK: u64 = ((1_u64 << 10) - 1) << Self::KEY_LENGTH_SHIFT;
+    const VALUE_LENGTH_MASK: u64 = ((1_u64 << 24) - 1) << Self::VALUE_LENGTH_SHIFT;
+
+    const MAX_KEY_LENGTH: usize = (1 << 10) - 2;
+    const MAX_VALUE_LENGTH: usize = (1 << 24) - 2;
+
+    pub(super) const fn new_inline(key_len: usize, value_len: usize) -> Self {
+        assert!(
+            key_len <= Self::MAX_KEY_LENGTH,
+            "key length exceeds header field"
+        );
+        assert!(
+            value_len <= Self::MAX_VALUE_LENGTH,
+            "value length exceeds header field"
+        );
+
+        Self(
+            Self::KEY_INLINE_BIT
+                | Self::VALUE_INLINE_BIT
+                | ((key_len as u64) << Self::KEY_LENGTH_SHIFT)
+                | ((value_len as u64) << Self::VALUE_LENGTH_SHIFT),
+        )
+    }
+
+    pub(super) const fn from_raw(raw: u64) -> Self {
+        Self(raw)
+    }
+
+    pub(super) const fn as_raw(self) -> u64 {
+        self.0
+    }
+
+    pub(super) const fn key_is_inline(self) -> bool {
+        self.0 & Self::KEY_INLINE_BIT != 0
+    }
+
+    pub(super) const fn value_is_inline(self) -> bool {
+        self.0 & Self::VALUE_INLINE_BIT != 0
+    }
+
+    pub(super) const fn key_len(self) -> usize {
+        ((self.0 & Self::KEY_LENGTH_MASK) >> Self::KEY_LENGTH_SHIFT) as usize
+    }
+
+    pub(super) const fn value_len(self) -> usize {
+        ((self.0 & Self::VALUE_LENGTH_MASK) >> Self::VALUE_LENGTH_SHIFT) as usize
+    }
+
+    pub(super) const fn filler_words(self) -> usize {
+        ((self.0 & Self::FILLER_WORDS_MASK) >> Self::FILLER_WORDS_SHIFT) as usize
+    }
+
+    pub(super) const fn allocated_len(self) -> usize {
+        let unaligned = HEADER_SIZE + self.key_len() + self.value_len();
+
+        let aligned = unaligned.next_multiple_of(ALIGNMENT);
+
+        aligned + self.filler_words() * ALIGNMENT
+    }
+}

src/record/mod.rs

@@ -1,3 +1,4 @@
+mod data_header;
 mod info;
 
 use crate::address::Address;