boiler to manage scan encoding

src/output.zig

@@ -2,9 +2,53 @@ const std = @import("std");
 
 const util = @import("util.zig");
 
+const RLE_Seq = std.ArrayList(RLE_Unit);
+const RLE_Unit = struct {
+    symbol: u8,
+    value: i16,
+};
+
+const Huffman = std.AutoHashMap(u8, HuffCode);
+const HuffCode = struct {
+    n_bits: u8,
+    value: u16,
+};
+
+const Scan = struct {
+    arena: std.heap.ArenaAllocator,
+    diffs: [3]i16,
+    rles: [3]RLE_Seq,
+    freqs: [4][]u32,
+    huffs: [4]Huffman,
+
+    const Self = @This();
+
+    fn init(alloc_: std.mem.Allocator) !Self {
+        var arena = std.heap.ArenaAllocator.init(alloc_);
+        var alloc = arena.allocator();
+        return Self{ .arena = arena, .diffs = [3]i16{ 0, 0, 0 }, .rles = [3]RLE_Seq{
+            RLE_Seq.init(alloc),
+            RLE_Seq.init(alloc),
+            RLE_Seq.init(alloc),
+        }, .freqs = [4][]u32{ try alloc.alloc(u32, 257), try alloc.alloc(u32, 257), try alloc.alloc(u32, 257), try alloc.alloc(u32, 257) }, .huffs = [4]Huffman{
+            Huffman.init(alloc),
+            Huffman.init(alloc),
+            Huffman.init(alloc),
+            Huffman.init(alloc),
+        } };
+    }
+    fn deinit(self: *Self) void {
+        self.arena.deinit();
+    }
+};
+
 pub fn generate_jpg(buff: util.Buffers, alloc: std.mem.Allocator) !void {
-    _ = alloc;
     _ = buff;
+    var scan_data = try Scan.init(alloc);
+    defer scan_data.deinit();
+
+    scan_data.do_rle_freq_pass(buff);
+
     // rle, huffman pass
     // file headers
     // quant + huffman write