1 files changed, 122 insertions, 0 deletions
diff --git a/src/jpg/marker.zig b/src/jpg/marker.zig
new file mode 100644
index 0000000..63eefe5
--- /dev/null
+++ b/src/jpg/marker.zig
@@ -0,0 +1,122 @@
+const std = @import("std");
+
+pub const Marker = union(enum) {
+    pub const Kind = std.meta.Tag(@This());
+
+    const Tag = struct {
+        const temporary = 0x1;
+        const reset = .{ .start = 0xd0, .end = 0xd7 };
+        const start_of_frame = .{
+            .{ .start = 0xc0, .end = 0xc3 },
+            .{ .start = 0xc5, .end = 0xc7 },
+            .{ .start = 0xc9, .end = 0xcb },
+        };
+        const start_of_image = 0xd8;
+        const end_of_image = 0xd9;
+        const define_quantization_table = 0xdb;
+        const define_huffman_table = 0xc4;
+        const define_restart_interval = 0xdd;
+        const define_number_of_lines = 0xdc;
+        const define_hierarchy_progression = 0xde;
+        const extend_huffman_table = 0xdf;
+        const application_segment = .{ .start = 0xe0, .end = 0xef };
+        const comment = 0xfe;
+        const start_of_scan = 0xda;
+    };
+
+    temporary: void,
+    reset: u3,
+    start_of_image: void,
+    end_of_image: void,
+    start_of_frame: u4,
+    define_quantization_table: void,
+    define_huffman_table: void,
+    define_restart_interval: void,
+    define_number_of_lines: void,
+    define_hierarchy_progression: void,
+    extend_huffman_table: void,
+    application_segment: u4,
+    comment: void,
+    start_of_scan: void,
+
+
+    pub fn from_u8(value: u8) !@This() {
+        return switch (value) {
+            Tag.reset.start...Tag.reset.end => .{
+                .reset = @intCast(value - Tag.reset.start),
+            },
+            Tag.start_of_frame[0].start...Tag.start_of_frame[0].end => .{
+                .start_of_frame = @intCast(value - Tag.start_of_frame[0].start),
+            },
+            Tag.start_of_frame[1].start...Tag.start_of_frame[1].end => .{
+                .start_of_frame = @intCast(value - Tag.start_of_frame[1].start + 4),
+            },
+            Tag.start_of_frame[2].start...Tag.start_of_frame[2].end => .{
+                .start_of_frame = @intCast(value - Tag.start_of_frame[2].start + 7),
+            },
+            Tag.application_segment.start...Tag.application_segment.end => .{
+                .application_segment = @intCast(value - Tag.application_segment.start),
+            },
+            Tag.start_of_image => .{ .start_of_image = void{} },
+            Tag.end_of_image => .{ .end_of_image = void{} },
+            Tag.define_quantization_table => .{ .define_quantization_table = void{} },
+            Tag.define_huffman_table => .{ .define_huffman_table = void{} },
+            Tag.define_restart_interval => .{ .define_restart_interval = void{} },
+            Tag.define_number_of_lines => .{ .define_number_of_lines = void{} },
+            Tag.define_hierarchy_progression => .{ .define_hierarchy_progression = void{} },
+            Tag.extend_huffman_table => .{ .extend_huffman_table = void{} },
+            Tag.comment => .{ .comment = void{} },
+            Tag.start_of_scan => .{ .start_of_scan = void{} },
+            Tag.temporary => .{ .temporary = void{} },
+            else => error.InvalidByte,
+        };
+    }
+};
+
+test "marker" {
+    const Testing = struct {
+        pub fn empty_tag(value: comptime_int, tag: std.meta.Tag(Marker)) !void {
+            const marker: Marker = try .from_u8(value);
+            try std.testing.expectEqual(
+                tag,
+                std.meta.activeTag(marker),
+            );
+        }
+    };
+
+    for (0..8) |offset| {
+        const marker: Marker = try .from_u8(0xd0 + @as(u8, @intCast(offset)));
+        try std.testing.expectEqual(offset, marker.reset);
+    }
+
+    {
+        for (0..4) |offset| {
+            const marker: Marker = try .from_u8(0xc0 + @as(u8, @intCast(offset)));
+            try std.testing.expectEqual(offset, marker.start_of_frame);
+        }
+
+        for (0..3) |offset| {
+            const marker: Marker = try .from_u8(0xc5 + @as(u8, @intCast(offset)));
+            try std.testing.expectEqual(offset + 4, marker.start_of_frame);
+        }
+
+        for (0..3) |offset| {
+            const marker: Marker = try .from_u8(0xc9 + @as(u8, @intCast(offset)));
+            try std.testing.expectEqual(offset + 7, marker.start_of_frame);
+        }
+    }
+
+    for (0..16) |offset| {
+        const marker: Marker = try .from_u8(0xe0 + @as(u8, @intCast(offset)));
+        try std.testing.expectEqual(offset, marker.application_segment);
+    }
+
+    try Testing.empty_tag(Marker.Tag.temporary, .temporary);
+    try Testing.empty_tag(Marker.Tag.start_of_image, .start_of_image);
+    try Testing.empty_tag(Marker.Tag.end_of_image, .end_of_image);
+    try Testing.empty_tag(Marker.Tag.define_quantization_table, .define_quantization_table);
+    try Testing.empty_tag(Marker.Tag.define_huffman_table, .define_huffman_table);
+    try Testing.empty_tag(Marker.Tag.define_restart_interval, .define_restart_interval);
+    try Testing.empty_tag(Marker.Tag.define_number_of_lines, .define_number_of_lines);
+    try Testing.empty_tag(Marker.Tag.define_hierarchy_progression, .define_hierarchy_progression);
+}