SeenPcsHeader

    pub const SeenPcsHeader = extern struct {
        n_runs: usize,
        unique_runs: usize,
        pcs_len: usize,

        /// Used for comptime assertions. Provides a mechanism for strategically
        /// causing compile errors.
        pub const trailing = .{
            .pc_bits_usize,
            .pc_addr,
        };

        pub fn headerEnd(header: *const SeenPcsHeader) []const usize {
            const ptr: [*]align(@alignOf(usize)) const u8 = @ptrCast(header);
            const header_end_ptr: [*]const usize = @ptrCast(ptr + @sizeOf(SeenPcsHeader));
            const pcs_len = header.pcs_len;
            return header_end_ptr[0 .. pcs_len + seenElemsLen(pcs_len)];
        }

        pub fn seenBits(header: *const SeenPcsHeader) []const usize {
            return header.headerEnd()[0..seenElemsLen(header.pcs_len)];
        }

        pub fn seenElemsLen(pcs_len: usize) usize {
            return (pcs_len + @bitSizeOf(usize) - 1) / @bitSizeOf(usize);
        }

        pub fn pcAddrs(header: *const SeenPcsHeader) []const usize {
            const pcs_len = header.pcs_len;
            return header.headerEnd()[seenElemsLen(pcs_len)..][0..pcs_len];
        }
    }