Introduce align_up() helper function

Introduce a helper function that can be used for aligning values to the
next power of two.

Signed-off-by: Daniel Müller <[email protected]>

src/dwarf/debug_link.rs

@@ -20,6 +20,7 @@ use std::path::PathBuf;
 
 use crate::elf::ElfParser;
 use crate::error::IntoError as _;
+use crate::util::align_up;
 use crate::util::bytes_to_os_str;
 use crate::util::ReadRaw as _;
 use crate::Result;
@@ -161,7 +162,7 @@ fn parse_debug_link_section_data(mut data: &[u8]) -> Result<Option<(&OsStr, u32)
     // The offset is aligned to the next four byte boundary relative to
     // the start of the section.
     let align = 4;
-    let crc_offset = (cur_offset + (align - 1)) & !(align - 1);
+    let crc_offset = align_up(cur_offset, align);
     let () = data
         .advance(crc_offset - cur_offset)
         .ok_or_invalid_data(|| {

src/util.rs

@@ -82,6 +82,17 @@ where
 }
 
 
+/// Align a value to the next power of two.
+pub(crate) fn align_up(value: usize, align_to: usize) -> usize {
+    debug_assert_eq!(
+        align_to.next_power_of_two(),
+        align_to,
+        "alignment ({align_to}) is no power of two"
+    );
+    (value + (align_to - 1)) & !(align_to - 1)
+}
+
+
 /// Split a byte slice at the first byte for which `check` returns
 /// `true`.
 ///
@@ -718,6 +729,28 @@ mod tests {
         );
     }
 
+    /// Check that we can properly align values to a power of two.
+    #[tag(miri)]
+    #[test]
+    fn upwards_alignment() {
+        assert_eq!(align_up(0, 4), 0);
+        assert_eq!(align_up(1, 4), 4);
+        assert_eq!(align_up(2, 4), 4);
+        assert_eq!(align_up(3, 4), 4);
+        assert_eq!(align_up(4, 4), 4);
+        assert_eq!(align_up(5, 4), 8);
+    }
+
+    /// Make sure that `align_up` panics when attempting to align to
+    /// something other than a power of two.
+    #[cfg(debug_assertions)]
+    #[tag(miri)]
+    #[test]
+    #[should_panic = "alignment (3) is no power of two"]
+    fn upwards_alignment_no_power_of_two() {
+        assert_eq!(align_up(0, 3), 0);
+    }
+
     /// Check that we can reorder elements in an array as expected.
     #[tag(miri)]
     #[test]