diff --git a/tools/applypatch/imgpatch.c b/tools/applypatch/imgpatch.c
new file mode 100644
index 0000000..f4abc60
--- /dev/null
+++ b/tools/applypatch/imgpatch.c
@@ -0,0 +1,227 @@
+/*
+ * Copyright (C) 2009 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// See imgdiff.c in this directory for a description of the patch file
+// format.
+
+#include <stdio.h>
+#include <sys/stat.h>
+#include <errno.h>
+#include <unistd.h>
+#include <string.h>
+
+#include "zlib.h"
+#include "mincrypt/sha.h"
+#include "applypatch.h"
+#include "imgdiff.h"
+
+int Read4(unsigned char* p) {
+  return (int)(((unsigned int)p[3] << 24) |
+               ((unsigned int)p[2] << 16) |
+               ((unsigned int)p[1] << 8) |
+               (unsigned int)p[0]);
+}
+
+long long Read8(unsigned char* p) {
+  return (long long)(((unsigned long long)p[7] << 56) |
+                     ((unsigned long long)p[6] << 48) |
+                     ((unsigned long long)p[5] << 40) |
+                     ((unsigned long long)p[4] << 32) |
+                     ((unsigned long long)p[3] << 24) |
+                     ((unsigned long long)p[2] << 16) |
+                     ((unsigned long long)p[1] << 8) |
+                     (unsigned long long)p[0]);
+}
+
+/*
+ * Apply the patch given in 'patch_filename' to the source data given
+ * by (old_data, old_size).  Write the patched output to the 'output'
+ * file, and update the SHA context with the output data as well.
+ * Return 0 on success.
+ */
+int ApplyImagePatch(const unsigned char* old_data, ssize_t old_size,
+                    const char* patch_filename,
+                    FILE* output, SHA_CTX* ctx) {
+  FILE* f;
+  if ((f = fopen(patch_filename, "rb")) == NULL) {
+    fprintf(stderr, "failed to open patch file\n");
+    return -1;
+  }
+
+  unsigned char header[12];
+  if (fread(header, 1, 12, f) != 12) {
+    fprintf(stderr, "failed to read patch file header\n");
+    return -1;
+  }
+
+  if (memcmp(header, "IMGDIFF1", 8) != 0) {
+    fprintf(stderr, "corrupt patch file header (magic number)\n");
+    return -1;
+  }
+
+  int num_chunks = Read4(header+8);
+
+  int i;
+  for (i = 0; i < num_chunks; ++i) {
+    // each chunk's header record starts with 28 bytes (4 + 8*3).
+    unsigned char chunk[28];
+    if (fread(chunk, 1, 28, f) != 28) {
+      fprintf(stderr, "failed to read chunk %d record\n", i);
+      return -1;
+    }
+
+    int type = Read4(chunk);
+    size_t src_start = Read8(chunk+4);
+    size_t src_len = Read8(chunk+12);
+    size_t patch_offset = Read8(chunk+20);
+
+    if (type == CHUNK_NORMAL) {
+      fprintf(stderr, "CHUNK %d:  normal   patch offset %d\n", i, patch_offset);
+
+      ApplyBSDiffPatch(old_data + src_start, src_len,
+                       patch_filename, patch_offset,
+                       output, ctx);
+    } else if (type == CHUNK_GZIP) {
+      fprintf(stderr, "CHUNK %d:  gzip     patch offset %d\n", i, patch_offset);
+
+      // gzip chunks have an additional 40 + gzip_header_len + 8 bytes
+      // in their chunk header.
+      unsigned char* gzip = malloc(40);
+      if (fread(gzip, 1, 40, f) != 40) {
+        fprintf(stderr, "failed to read chunk %d initial gzip data\n", i);
+        return -1;
+      }
+      size_t gzip_header_len = Read4(gzip+36);
+      gzip = realloc(gzip, 40 + gzip_header_len + 8);
+      if (fread(gzip+40, 1, gzip_header_len+8, f) != gzip_header_len+8) {
+        fprintf(stderr, "failed to read chunk %d remaining gzip data\n", i);
+        return -1;
+      }
+
+      size_t expanded_len = Read8(gzip);
+      size_t target_len = Read8(gzip);
+      int gz_level = Read4(gzip+16);
+      int gz_method = Read4(gzip+20);
+      int gz_windowBits = Read4(gzip+24);
+      int gz_memLevel = Read4(gzip+28);
+      int gz_strategy = Read4(gzip+32);
+
+      // Decompress the source data; the chunk header tells us exactly
+      // how big we expect it to be when decompressed.
+
+      unsigned char* expanded_source = malloc(expanded_len);
+      if (expanded_source == NULL) {
+        fprintf(stderr, "failed to allocate %d bytes for expanded_source\n", expanded_len);
+        return -1;
+      }
+
+      z_stream strm;
+      strm.zalloc = Z_NULL;
+      strm.zfree = Z_NULL;
+      strm.opaque = Z_NULL;
+      strm.avail_in = src_len - (gzip_header_len + 8);
+      strm.next_in = (unsigned char*)(old_data + src_start + gzip_header_len);
+      strm.avail_out = expanded_len;
+      strm.next_out = expanded_source;
+
+      int ret;
+      ret = inflateInit2(&strm, -15);
+      if (ret != Z_OK) {
+        fprintf(stderr, "failed to init source inflation: %d\n", ret);
+        return -1;
+      }
+
+      // Because we've provided enough room to accommodate the output
+      // data, we expect one call to inflate() to suffice.
+      ret = inflate(&strm, Z_SYNC_FLUSH);
+      if (ret != Z_STREAM_END) {
+        fprintf(stderr, "source inflation returned %d\n", ret);
+        return -1;
+      }
+      // We should have filled the output buffer exactly.
+      if (strm.avail_out != 0) {
+        fprintf(stderr, "source inflation short by %d bytes\n", strm.avail_out);
+        return -1;
+      }
+      inflateEnd(&strm);
+
+      // Next, apply the bsdiff patch (in memory) to the uncompressed
+      // data.
+      unsigned char* uncompressed_target_data;
+      ssize_t uncompressed_target_size;
+      if (ApplyBSDiffPatchMem(expanded_source, expanded_len,
+                              patch_filename, patch_offset,
+                              &uncompressed_target_data,
+                              &uncompressed_target_size) != 0) {
+        return -1;
+      }
+
+      // Now compress the target data and append it to the output.
+
+      // start with the gzip header.
+      fwrite(gzip+40, 1, gzip_header_len, output);
+      SHA_update(ctx, gzip+40, gzip_header_len);
+
+      // we're done with the expanded_source data buffer, so we'll
+      // reuse that memory to receive the output of deflate.
+      unsigned char* temp_data = expanded_source;
+      ssize_t temp_size = expanded_len;
+      if (temp_size < 32768) {
+        // ... unless the buffer is too small, in which case we'll
+        // allocate a fresh one.
+        free(temp_data);
+        temp_data = malloc(32768);
+        temp_size = 32768;
+      }
+
+      // now the deflate stream
+      strm.zalloc = Z_NULL;
+      strm.zfree = Z_NULL;
+      strm.opaque = Z_NULL;
+      strm.avail_in = uncompressed_target_size;
+      strm.next_in = uncompressed_target_data;
+      ret = deflateInit2(&strm, gz_level, gz_method, gz_windowBits,
+                         gz_memLevel, gz_strategy);
+      do {
+        strm.avail_out = temp_size;
+        strm.next_out = temp_data;
+        ret = deflate(&strm, Z_FINISH);
+        size_t have = temp_size - strm.avail_out;
+
+        if (fwrite(temp_data, 1, have, output) != have) {
+          fprintf(stderr, "failed to write %d compressed bytes to output\n",
+                  have);
+          return -1;
+        }
+        SHA_update(ctx, temp_data, have);
+      } while (ret != Z_STREAM_END);
+      deflateEnd(&strm);
+
+      // lastly, the gzip footer.
+      fwrite(gzip+40+gzip_header_len, 1, 8, output);
+      SHA_update(ctx, gzip+40+gzip_header_len, 8);
+
+      free(temp_data);
+      free(uncompressed_target_data);
+      free(gzip);
+    } else {
+      fprintf(stderr, "patch chunk %d is unknown type %d\n", i, type);
+      return -1;
+    }
+  }
+
+  return 0;
+}