Add support for IPS patching

Adds support for patching ROMs on the fly with a corresponding IPS patch
file. Functions in a similar manner to the pre-existing BPS support. If
a *.ips file is found with the same name as the ROM, it attempts to
apply the patch. If both a BPS and IPS file are found, the BPS patch
takes priority. This patch implements the IPS format as described here:
https://zerosoft.zophar.net/ips.php

mia/mia.hpp

@@ -1,5 +1,6 @@
 #include <nall/nall.hpp>
 #include <nall/cd.hpp>
+#include <nall/ips.hpp>
 #include <nall/vfs.hpp>
 #include <nall/beat/single/apply.hpp>
 #include <nall/decode/cue.hpp>

mia/pak/pak.cpp

@@ -24,11 +24,15 @@ auto Pak::read(string location) -> vector<u8> {
 
 auto Pak::read(string location, vector<string> match) -> vector<u8> {
   vector<u8> memory;
-  vector<u8> patch;
+  vector<u8> ips_patch;
+  vector<u8> bps_patch;
 
   if(file::exists(location)) {
-    //support BPS patches next to the file
-    patch = file::read({Location::notsuffix(location), ".bps"});
+    //support IPS or BPS patches next to the file
+    bps_patch = file::read({Location::notsuffix(location), ".bps"});
+    if (!bps_patch) {
+      ips_patch = file::read({Location::notsuffix(location), ".ips"});
+    }
 
     if(location.iendsWith(".zip")) {
       Decode::ZIP archive;
@@ -46,7 +50,10 @@ auto Pak::read(string location, vector<string> match) -> vector<u8> {
           //support BPS patches inside the ZIP archive
           for(auto& file : archive.file) {
             if(file.name.imatch("*.bps")) {
-              patch = archive.extract(file);
+              bps_patch = archive.extract(file);
+              break;
+            } else if (file.name.imatch("*.ips")) {
+              ips_patch = archive.extract(file);
               break;
             }
           }
@@ -62,9 +69,13 @@ auto Pak::read(string location, vector<string> match) -> vector<u8> {
     }
   }
 
-  //attempt to apply BPS patch if one was found
-  if(patch) {
-    if(auto output = Beat::Single::apply(memory, patch)) {
+  //attempt to apply IPS or BPS patch if one was found, favoring BPS
+  if(bps_patch) {
+    if(auto output = Beat::Single::apply(memory, bps_patch)) {
+      memory = std::move(*output);
+    }
+  } else if (ips_patch) {
+    if (auto output = IPS::apply(memory, ips_patch)) {
       memory = std::move(*output);
     }
   }

nall/ips.hpp

@@ -0,0 +1,63 @@
+#pragma once
+
+namespace nall::IPS {
+
+inline auto apply(array_view<u8> source, array_view<u8> patch, maybe<string&> result = {}) -> maybe<vector<u8>> {
+    #define error(text) { if(result) *result = {"error: ", text}; return {}; }
+    #define success() { if(result) *result = ""; return target; }
+
+    vector<u8> target;
+    for (u32 i : range(source.size())) {
+        target.append(source[i]);
+    }
+
+    u32 patchOffset = 0;
+    auto read = [&]() -> u8 {
+        return patch[patchOffset++];
+    };
+    auto readOffset = [&]() -> u32 {
+        u32 result = read() << 16;
+        result |= read() << 8;
+        result |= read();
+        return result;
+    };
+    auto readLength = [&]() -> u32 {
+        u32 result = read() << 8;
+        result |= read();
+        return result;
+    };
+    auto write = [&](u32 index, u8 data) {
+        target[index] = data;
+    };
+
+    if(read() != 'P') error("IPS header invalid");
+    if(read() != 'A') error("IPS header invalid");
+    if(read() != 'T') error("IPS header invalid");
+    if(read() != 'C') error("IPS header invalid");
+    if(read() != 'H') error("IPS header invalid");
+
+    u32 patchSize = patch.size();
+    while (patchOffset < patchSize - 3) {
+        u32 offset = readOffset();
+        u32 length = readLength();
+
+        if(target.size() < offset + length) error("Invalid IPS patch file");
+
+        if (length == 0) {
+            length = readLength();
+            u8 data = read();
+            for(u32 i : range(length)) write(offset + i, data);
+        } else {
+            for (u32 i : range(length)) write(offset + i, read());
+        }
+    }
+
+    if(read() != 'E') error("IPS footer invalid");
+    if(read() != 'O') error("IPS footer invalid");
+    if(read() != 'F') error("IPS footer invalid");
+
+    success();
+    #undef error
+    #undef success
+}
+}