patterns: Add ZIM pattern (#367)

* Add ZIM pattern file

* Add test file

* namespace!

README.md

@@ -179,6 +179,7 @@ Everything will immediately show up in ImHex's Content Store and gets bundled wi
 | XGT | | [`patterns/xgt.hexpat`](patterns/xgstexture.hexpat) | Exient XGS Engine Texture |
 | Xilinx BIT | | [`patterns/xilinx_bit.hexpat`](patterns/xilinx_bit.hexpat) | Xilinx FPGA Bitstreams |
 | Xilinx Bootgen | `application/x-xilinx-boot-zynqmp` | [`patterns/xilinx_bootgen.hexpat`](patterns/xilinx_bootgen.hexpat) | Xilinx ZynqMP Boot Images |
+| ZIM  | | [`patterns/zim.hexpat`](patterns/zim.hexpat) | [ZIM](https://openzim.org) file format |
 | ZIP  | `application/zip` | [`patterns/zip.hexpat`](patterns/zip.hexpat) | End of Central Directory Header, Central Directory File Headers |
 | ZLIB | `application/zlib` | [`patterns/zlib.hexpat`](patterns/zlib.hexpat) | ZLIB compressed data format |
 | ZSTD | `application/zstd` | [`patterns/zstd.hexpat`](patterns/zstd.hexpat) | Zstandard compressed data format |

patterns/zim.hexpat

@@ -0,0 +1,79 @@
+#pragma endian little
+#pragma description ZIM file format
+#pragma magic [ 5A 49 4D 04 ] @ 0x00
+
+u32 maxEntries in;
+
+import std.string;
+import std.mem;
+import std.math;
+import std.core;
+
+struct Header {
+    char signature[4];
+    u16 majorVersion;
+    u16 minorVersion;
+    u128 uid;
+    u32 entryCount, clusterCount;
+    u64 pathPtrPos, titlePtrPos, clusterPtrPos, mimeListPos;
+    u32 mainPage;
+    u32 layoutPage;
+    u64 checksumPos;
+};
+
+
+Header header @ 0x00;
+std::string::NullString mimeTypes[while(std::mem::read_unsigned($, 1) != 0x00)] @ header.mimeListPos;
+
+fn mimename(u16 index) {
+    if(index == 0xFFFF) {
+        return "redirect";
+    } else {
+        return mimeTypes[index];
+    }
+};
+
+enum CompressionType : u8 {
+    None = 0x01,
+    LZMA2 = 0x04,
+    zstd = 0x05
+};
+
+bitfield ClusterInfo {
+    CompressionType compression: 4;
+    offsetSize: 1;
+} [[bitfield_order(std::core::BitfieldOrder::LeastToMostSignificant, 8)]];
+
+struct Cluster {
+    ClusterInfo info;
+} [[inline]];
+
+struct ClusterPointer {
+    Cluster *cluster: u64;
+} [[inline]];
+
+struct Entry {
+    u16 mimetype [[format("mimename")]];
+    u8 parameterlen [[hidden]];
+    char _namespace [[name("namespace")]];
+    u32 revision;
+    if (mimetype == 0xFFFF) {
+        u32 redirectIndex;
+    } else {
+        u32 clusterNumber;
+        ClusterPointer cluster @ (header.clusterPtrPos + clusterNumber * 8);
+        u32 blobNumber;
+    }
+
+    std::string::NullString path;
+    std::string::NullString title;
+    padding[parameterlen];
+} [[inline]];
+
+struct EntryPointer {
+    Entry *entry : u64;
+} [[inline]];
+
+EntryPointer pathPointerList[std::math::min(header.entryCount, maxEntries == 0 ? 1500 : maxEntries)] @ header.pathPtrPos;
+u32 titlePointerList[header.entryCount] @ header.titlePtrPos;
+