started working on the bit walker

src/main.zig

@@ -20,6 +20,74 @@ fn usage() void {
     exit("", .{}, 1);
 }
 
+const BitWalker = struct {
+    const Self = @This();
+
+    data: *[]u8,
+    position: usize = 0,
+    in_byte_position: u3 = 0,
+    direction: bool = false,
+
+    fn init(data: *[]u8, direction: bool) Self {
+        return Self{
+            .data = data,
+            .direction = direction,
+        };
+    }
+
+    // TODO direction
+    fn walk(self: *Self, bits: u3) !u8 {
+        if (bits > 8 or bits == 0) return error.invalid_bit_number;
+        var byte = self.data.ptr[self.position];
+
+        // jumps over bytes
+        if (self.in_byte_position + @as(u4, bits) > 8) {
+            // Generate a mast that covers the last part of the old byte
+            var old_mask: u8 = 0;
+            var i: usize = 0;
+            while (i < bits - self.in_byte_position) : (i += 1) {
+                old_mask = @shlExact(old_mask, 1) + 1;
+            }
+            old_mask = @shlExact(old_mask, self.in_byte_position);
+
+            var next_byte = self.data.ptr[self.position + 1];
+            var new_byte_pos: u3 = self.in_byte_position + bits % 8;
+
+            var new_mask: u8 = 0;
+            var j: usize = 0;
+            while (j < new_byte_pos) : (j += 1) {
+                new_mask = @shlExact(new_mask, 1) + 1;
+            }
+            print("{} mask: {b}, new_mask", .{ bits, old_mask, new_mask });
+            print("here {b} {b}", .{ byte, old_mask });
+            print("here_new {b} {b}", .{ next_byte, new_mask });
+
+            self.position += 1;
+            self.in_byte_position = new_byte_pos;
+            return byte & old_mask + next_byte & new_mask;
+        }
+
+        // Generate a mast that covers the last part of the old byte
+        var old_mask: u8 = 0;
+        var i: usize = 0;
+        while (i < bits) : (i += 1) {
+            old_mask = @shlExact(old_mask, 1) + 1;
+        }
+        old_mask = @shlExact(old_mask, self.in_byte_position);
+
+        if (self.in_byte_position + bits == 8) {
+            self.position += 1;
+            self.in_byte_position = 0;
+        }
+
+        const result = @shrExact(byte & old_mask, self.in_byte_position);
+
+        self.in_byte_position += bits;
+
+        return result;
+    }
+};
+
 const LOCAL_FILE_HEADER_SIGNATURE = 0x04034b50;
 const ZipFileHeader = struct {
     version: u16,
@@ -92,11 +160,26 @@ const ZipFileHeader = struct {
         }
 
         self.uncompressed_content = try self.allocator.alloc(u8, self.uncompressed_size);
-        errdefer self.allocator.free(self.uncompressed_size);
+        errdefer self.allocator.free(self.uncompressed_content);
+
+        var bitw = BitWalker.init(&self.compressed_content, false);
+
+        var lastBlock1 = try bitw.walk(1);
+        var blockType1 = try bitw.walk(2);
+        var number_of_literal_codes1 = try bitw.walk(5);
+        var number_of_dist_codes1 = try bitw.walk(5);
+
+        print("{} {} {} {}", .{ lastBlock1, blockType1, number_of_literal_codes1, number_of_dist_codes1 });
 
         var byte = self.compressed_content[0];
-        var lastBlock = byte & 0b1000_0000 == 0b1000_0000;
+        var lastBlock = byte & 0b0000_0001 == 0b0000_0001;
-        var blockType = @shrExact(byte & 0b0110_0000, 5);
+        var blockType = @shrExact(byte & 0b0000_0110, 1);
+        var number_of_literal_codes = @shrExact(byte & 0b1111_1000, 3); // 256
+        byte = self.compressed_content[1];
+        var number_of_dist_codes = byte & 0b0001_1111;
+        var next_byte = self.compressed_content[2];
+        var number_of_length_codes = @shrExact(byte & 0b1110_0000, 5) + @shlExact(next_byte & 0b0000_0001, 3);
+        byte = next_byte;
 
         if (lastBlock) {
             print("last block", .{});
@@ -104,12 +187,16 @@ const ZipFileHeader = struct {
             print("not last block", .{});
         }
 
-        print("blockType: {}", .{blockType});
+        print("block_type: {}", .{blockType});
 
         if (blockType != 2) {
             return error.unsuported_block_type;
         }
 
+        print("number of literal codes: {}", .{number_of_literal_codes});
+        print("number of dist codes: {}", .{number_of_dist_codes});
+        print("number_of_length_coes: {}", .{number_of_length_codes});
+
         self.decompressed = true;
     }