add huffman boiler, Code_size impl

src/output.zig

@@ -58,9 +58,73 @@ const Scan = struct {
                 try parse_block(&buff.V_quant[x][y], &self.dc_diffs[2], &self.rles[2], self.freqs[2], self.freqs[3]);
             }
         }
+        try self.generate_huffmans();
+    }
+
+    fn generate_huffmans(self: *Self) !void {
+        for (0..4) |i| {
+            try gen_huffman(&self.huffs[i], self.freqs[i]);
+        }
     }
 };
 
+inline fn get_idx_min2(freqs: []u32) ?struct { usize, usize } {
+    var min1: u32 = undefined;
+    var min1_idx: usize = undefined;
+    var min2: u32 = undefined;
+    var min2_idx: usize = undefined;
+    var is_init_1 = false;
+    var is_init_2 = false;
+    for (0..freqs.len) |i| {
+        if (freqs[i] == 0) continue;
+        if (!is_init_1) {
+            min1 = freqs[i];
+            min1_idx = i;
+        } else if (!is_init_2) {
+            if (freqs[i] < min1) {
+                min2 = min1;
+                min2_idx = min1_idx;
+                min1 = freqs[i];
+                min1_idx = i;
+            } else {
+                min2 = freqs[i];
+                min2_idx = i;
+            }
+        } else if (freqs[i] < min1) {
+            min1 = freqs[i];
+            min1_idx = i;
+        } else if (freqs[i] < min2) {
+            min2 = freqs[i];
+            min2_idx = i;
+        }
+    }
+    return if (is_init_2) .{
+        min1_idx,
+        min2_idx,
+    } else null;
+}
+
+inline fn gen_huffman(huff: *Huffman, freqs: []u32) !void {
+    _ = huff;
+    var codesizes = [_]u8{0} ** 257;
+    var others = [_]u9{0x1ff} ** 257;
+
+    while (get_idx_min2(freqs)) |tmp| {
+        var v1 = tmp.@"0";
+        var v2 = tmp.@"1";
+        freqs[v1] += freqs[v2];
+        codesizes[v1] += 1;
+        while (others[v1] != 0x1ff) : (codesizes[v1] += 1) {
+            v1 = others[v1];
+        }
+        others[v1] = @truncate(v2);
+        codesizes[v2] += 1;
+        while (others[v2] != 0x1ff) : (codesizes[v2] += 1) {
+            v2 = others[v2];
+        }
+    }
+}
+
 inline fn get_size(n: i16) u8 {
     if (n == 0) {
         return 0;