split calculation of lengths and offsets
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src/DB.zig
86
src/DB.zig
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@ -204,39 +204,73 @@ pub fn iov(self: *const DB) BoundedArray(os.iovec_const, DB_fields.len * 2) {
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return result;
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}
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pub fn fromBytes(buf: []align(8) const u8) InvalidHeader!DB {
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const header = try Header.fromBytes(buf[0..@sizeOf(Header)]);
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// At first the tuple below had field names too, but moved it to comments,
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// because it segfaulted. https://github.com/ziglang/zig/issues/3915 and
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// https://paste.sr.ht/~motiejus/2830736e796801517c1fa8639be6615cd56ada27
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const lengths = .{
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header.nblocks_bdz_gid, // bdz_gid
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header.nblocks_bdz_groupname, // bdz_groupname
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header.nblocks_bdz_uid, // bdz_uid
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header.nblocks_bdz_username, // bdz_username
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nblocks_n(u32, header.num_groups * 4), // idx_gid2group
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nblocks_n(u32, header.num_groups * 4), // idx_groupname2group
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nblocks_n(u32, header.num_users * 4), // idx_uid2user
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nblocks_n(u32, header.num_users * 4), // idx_name2user
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nblocks_n(u16, header.num_shells * 2), // shell_index
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header.nblocks_shell_blob, // shell_blob
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header.nblocks_groups, // groups
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header.nblocks_users, // users
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header.nblocks_groupmembers, // groupmembers
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header.nblocks_additional_gids, // additional_gids
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};
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const DBNumbers = struct {
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header: u64,
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bdz_gid: u64,
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bdz_groupname: u64,
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bdz_uid: u64,
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bdz_username: u64,
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idx_gid2group: u64,
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idx_groupname2group: u64,
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idx_uid2user: u64,
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idx_name2user: u64,
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shell_index: u64,
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shell_blob: u64,
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groups: u64,
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users: u64,
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groupmembers: u64,
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additional_gids: u64,
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};
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var result: DB = undefined;
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result.header = header;
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// in blocks
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fn fieldLengths(header: *const Header) DBNumbers {
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return DBNumbers{
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.header = undefined,
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.bdz_gid = header.nblocks_bdz_gid,
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.bdz_groupname = header.nblocks_bdz_groupname,
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.bdz_uid = header.nblocks_bdz_uid,
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.bdz_username = header.nblocks_bdz_username,
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.idx_gid2group = nblocks_n(u32, header.num_groups * 4),
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.idx_groupname2group = nblocks_n(u32, header.num_groups * 4),
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.idx_uid2user = nblocks_n(u32, header.num_users * 4),
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.idx_name2user = nblocks_n(u32, header.num_users * 4),
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.shell_index = nblocks_n(u16, header.num_shells * 2),
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.shell_blob = header.nblocks_shell_blob,
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.groups = header.nblocks_groups,
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.users = header.nblocks_users,
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.groupmembers = header.nblocks_groupmembers,
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.additional_gids = header.nblocks_additional_gids,
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};
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}
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// in blocks
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fn fieldOffsets(lengths: DBNumbers) DBNumbers {
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var result: DBNumbers = undefined;
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result.header = 0;
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var offset = comptime nblocks_n(u64, @sizeOf(Header));
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comptime assert(mem.eql(u8, DB_fields[0].name, "header"));
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inline for (DB_fields[1..]) |field, i| {
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const start = offset << section_length_bits;
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const end = (offset + lengths[i]) << section_length_bits;
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comptime assert(mem.eql(u8, field.name, meta.fields(DBNumbers)[i + 1].name));
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@field(result, field.name) = offset;
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offset += @field(lengths, field.name);
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}
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return result;
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}
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pub fn fromBytes(buf: []align(8) const u8) InvalidHeader!DB {
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const header = try Header.fromBytes(buf[0..@sizeOf(Header)]);
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const lengths = fieldLengths(header);
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const offsets = fieldOffsets(lengths);
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var result: DB = undefined;
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result.header = header;
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inline for (DB_fields[1..]) |field| {
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const start_block = @field(offsets, field.name);
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const end = (start_block + @field(lengths, field.name)) << section_length_bits;
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const start = start_block << section_length_bits;
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const slice_type = meta.Child(field.field_type);
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const value = mem.bytesAsSlice(slice_type, buf[start..end]);
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@field(result, field.name) = value;
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offset += lengths[i];
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}
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return result;
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