Support bps patching

Author: snesrev

src/main.c

@@ -902,27 +902,33 @@ static const char *kAssetFileCandidates[] = {
 };
 
 static void LoadAssets() {
-  const char *verify_failed = NULL;
-
   size_t length = 0;
   uint8 *data = NULL;
-  for (int i = 0; i < 2 && data == NULL; i++) {
+  for (int i = 0; i < 2 && data == NULL; i++)
     data = ReadWholeFile(kAssetFileCandidates[i], &length);
-    if (data && !VerifyAssetsFile(data, length)) {
-      verify_failed = kAssetFileCandidates[i];
-      free(data);
-      data = NULL;
-    }
-  }
 
   if (!data) {
-    if (verify_failed)
-      Die("Invalid assets file - Please re run 'python assets/restool.py'");
-    else
+    size_t bps_length, bps_src_length;
+    uint8 *bps, *bps_src;
+
+    bps = ReadWholeFile("smw_assets.bps", &bps_length);
+    if (!bps)
       Die("Failed to read smw_assets.dat. Please see the README for information about how you get this file.");
+    
+    bps_src = ReadWholeFile("smw.sfc", &bps_src_length);
+    if (!bps_src)
+      Die("Missing file: smw.sfc");
+    if (bps_src_length != 524288)
+      Die("smw.sfc needs to be the unheadered ROM");
+
+    data = ApplyBps(bps_src, bps_src_length, bps, bps_length, &length);
+    if (!data)
+      Die("Unable to apply smw_assets.bps");
   }
-  
 
+  if (!VerifyAssetsFile(data, length))
+    Die("Mismatching assets file - Please re run 'python assets/restool.py'");
+    
   uint32 offset = 88 + kNumberOfAssets * 4 + *(uint32 *)(data + 84);
 
   for (size_t i = 0; i < kNumberOfAssets; i++) {

src/util.c

@@ -237,3 +237,88 @@ const uint8 *FindAddrInMemblk(MemBlk data, uint32 addr) {
     return 0;
   return data.ptr + offset;
 }
+
+static uint64 BpsDecodeInt(const uint8 **src) {
+  uint64 data = 0, shift = 1;
+  while(true) {
+    uint8 x = *(*src)++;
+    data += (x & 0x7f) * shift;
+    if(x & 0x80) break;
+    shift <<= 7;
+    data += shift;
+  }
+  return data;
+}
+
+#define CRC32_POLYNOMIAL 0xEDB88320
+
+static uint32 crc32(const void *data, size_t length) {
+  uint32 crc = 0xFFFFFFFF;
+  const uint8 *byteData = (const uint8 *)data;
+  for (size_t i = 0; i < length; i++) {
+    crc ^= byteData[i];
+    for (int j = 0; j < 8; j++)
+      crc = (crc >> 1) ^ ((crc & 1) * CRC32_POLYNOMIAL);
+  }
+  return crc ^ 0xFFFFFFFF;
+}
+
+
+uint8 *ApplyBps(const uint8 *src, size_t src_size_in,
+                const uint8 *bps, size_t bps_size, size_t *length_out) {
+  const uint8 *bps_end = bps + bps_size - 12;
+
+  if (memcmp(bps, "BPS1", 4))
+    return NULL;
+  if (crc32(src, src_size_in) != *(uint32 *)(bps_end))
+    return NULL;
+  if (crc32(bps, bps_size - 4) != *(uint32 *)(bps_end + 8))
+    return NULL;
+
+  bps += 4;
+  uint32 src_size = BpsDecodeInt(&bps);
+  uint32 dst_size = BpsDecodeInt(&bps);
+  uint32 meta_size = BpsDecodeInt(&bps);
+  uint32 outputOffset = 0;
+  uint32 sourceRelativeOffset = 0;
+  uint32 targetRelativeOffset = 0;
+  if (src_size != src_size_in)
+    return NULL;
+  *length_out = dst_size;
+  uint8 *dst = malloc(dst_size);
+  if (!dst)
+    return NULL;
+  while (bps < bps_end) {
+    uint32 cmd = BpsDecodeInt(&bps);
+    uint32 length = (cmd >> 2) + 1;
+    switch (cmd & 3) {
+    case 0:
+      while(length--) {
+        dst[outputOffset] = src[outputOffset];
+        outputOffset++;
+      }
+      break;
+    case 1:
+      while (length--)
+        dst[outputOffset++] = *bps++;
+      break;
+    case 2:
+      cmd = BpsDecodeInt(&bps);
+      sourceRelativeOffset += (cmd & 1 ? -1 : +1) * (cmd >> 1);
+      while (length--)
+        dst[outputOffset++] = src[sourceRelativeOffset++];
+      break;
+    default:
+      cmd = BpsDecodeInt(&bps);
+      targetRelativeOffset += (cmd & 1 ? -1 : +1) * (cmd >> 1);
+      while(length--)
+        dst[outputOffset++] = dst[targetRelativeOffset++];
+      break;
+    }
+  }
+  if (dst_size != outputOffset)
+    return NULL;
+  if (crc32(dst, dst_size) != *(uint32 *)(bps_end + 4))
+    return NULL;
+  return dst;
+}

src/util.h

@@ -35,5 +35,7 @@ const char *SkipPrefix(const char *big, const char *little);
 void StrSet(char **rv, const char *s);
 char *StrFmt(const char *fmt, ...);
 char *ReplaceFilenameWithNewPath(const char *old_path, const char *new_path);
+uint8 *ApplyBps(const uint8 *src, size_t src_size_in,
+  const uint8 *bps, size_t bps_size, size_t *length_out);
 
 #endif  // ZELDA3_UTIL_H_