Method alloc

cranelift/entity/src/list.rs:193–212

Allocate a storage block with a size given by `sclass`. Returns the first index of an available segment of `self.data` containing `sclass_size(sclass)` elements. The allocated memory is filled with reserved values.

(&mut self, sclass: SizeClass)

    /// `sclass_size(sclass)` elements. The allocated memory is filled with reserved
    /// values.
    fn alloc(&mut self, sclass: SizeClass) -> usize {
        // First try the free list for this size class.
        match self.free.get(sclass as usize).cloned() {
            Some(head) if head > 0 => {
                // The free list pointers are offset by 1, using 0 to terminate the list.
                // A block on the free list has two entries: `[ 0, next ]`.
                // The 0 is where the length field would be stored for a block in use.
                // The free list heads and the next pointer point at the `next` field.
                self.free[sclass as usize] = self.data[head].index();
                head - 1
            }
            _ => {
                // Nothing on the free list. Allocate more memory.
                let offset = self.data.len();
                self.data
                    .resize(offset + sclass_size(sclass), T::reserved_value());
                offset
            }
        }
    }

    /// Free a storage block with a size given by `sclass`.
    ///