init

pub fn init(ranges_value: *const FormValue, di: *const Dwarf, compile_unit: *const CompileUnit) !@This() {
    const section_type = if (compile_unit.version >= 5) Section.Id.debug_rnglists else Section.Id.debug_ranges;
    const debug_ranges = di.section(section_type) orelse return error.MissingDebugInfo;

    const ranges_offset = switch (ranges_value.*) {
        .sec_offset, .udata => |off| off,
        .rnglistx => |idx| off: {
            switch (compile_unit.format) {
                .@"32" => {
                    const offset_loc = @as(usize, @intCast(compile_unit.rnglists_base + 4 * idx));
                    if (offset_loc + 4 > debug_ranges.len) return bad();
                    const offset = mem.readInt(u32, debug_ranges[offset_loc..][0..4], di.endian);
                    break :off compile_unit.rnglists_base + offset;
                },
                .@"64" => {
                    const offset_loc = @as(usize, @intCast(compile_unit.rnglists_base + 8 * idx));
                    if (offset_loc + 8 > debug_ranges.len) return bad();
                    const offset = mem.readInt(u64, debug_ranges[offset_loc..][0..8], di.endian);
                    break :off compile_unit.rnglists_base + offset;
                },
            }
        },
        else => return bad(),
    };

    // All the addresses in the list are relative to the value
    // specified by DW_AT.low_pc or to some other value encoded
    // in the list itself.
    // If no starting value is specified use zero.
    const base_address = compile_unit.die.getAttrAddr(di, AT.low_pc, compile_unit.*) catch |err| switch (err) {
        error.MissingDebugInfo => 0,
        else => return err,
    };

    return .{
        .base_address = base_address,
        .section_type = section_type,
        .di = di,
        .compile_unit = compile_unit,
        .fbr = .{
            .buf = debug_ranges,
            .pos = cast(usize, ranges_offset) orelse return bad(),
            .endian = di.endian,
        },
    };
}