diff --git a/ext4_utils/Android.mk b/ext4_utils/Android.mk
index 1470254..c7934a3 100644
--- a/ext4_utils/Android.mk
+++ b/ext4_utils/Android.mk
@@ -14,6 +14,7 @@
         indirect.c \
         uuid.c \
         sha1.c \
+	sparse_crc32.c
 
 LOCAL_SRC_FILES := $(libext4_utils_src_files)
 LOCAL_MODULE := libext4_utils
@@ -63,7 +64,8 @@
 
 include $(CLEAR_VARS)
 
-LOCAL_SRC_FILES := simg2img.c
+LOCAL_SRC_FILES := simg2img.c \
+	sparse_crc32.c
 LOCAL_MODULE := simg2img
 
 include $(BUILD_HOST_EXECUTABLE)
diff --git a/ext4_utils/output_file.c b/ext4_utils/output_file.c
index 2705701..3785b06 100644
--- a/ext4_utils/output_file.c
+++ b/ext4_utils/output_file.c
@@ -27,6 +27,7 @@
 #include "ext4_utils.h"
 #include "output_file.h"
 #include "sparse_format.h"
+#include "sparse_crc32.h"
 
 #if defined(__APPLE__) && defined(__MACH__)
 #define lseek64 lseek
@@ -148,7 +149,7 @@
 static int emit_skip_chunk(struct output_file *out, u64 skip_len)
 {
 	chunk_header_t chunk_header;
-	int ret;
+	int ret, chunk;
 
 	//DBG printf("skip chunk: 0x%llx bytes\n", skip_len);
 
@@ -166,10 +167,17 @@
 	ret = out->ops->write(out, (u8 *)&chunk_header, sizeof(chunk_header));
 	if (ret < 0)
 		return -1;
-	// KEN: TODO: CRC computation
+
 	out->cur_out_ptr += skip_len;
 	out->chunk_cnt++;
 
+	/* Compute the CRC for all those zeroes.  Do it block_size bytes at a time. */
+	while (skip_len) {
+		chunk = (skip_len > info.block_size) ? info.block_size : skip_len;
+		out->crc32 = sparse_crc32(out->crc32, zero_buf, chunk);
+		skip_len -= chunk;
+	}
+
 	return 0;
 }
 
@@ -231,7 +239,9 @@
 			return -1;
 	}
 
-	// KEN: TODO: CRC computation of both the raw data and and zero buf data written */
+	out->crc32 = sparse_crc32(out->crc32, data, len);
+	if (zero_len)
+		out->crc32 = sparse_crc32(out->crc32, zero_buf, zero_len);
 	out->cur_out_ptr += rnd_up_len;
 	out->chunk_cnt++;
 
@@ -293,6 +303,10 @@
 	out->sparse = sparse;
 	out->cur_out_ptr = 0ll;
 	out->chunk_cnt = 0;
+
+	/* Initialize the crc32 value */
+	out->crc32 = 0;
+
 	if (out->sparse) {
 		/* Write out the file header.  We'll update the unknown fields
 		 * when we close the file.
@@ -321,7 +335,6 @@
 		 * cur_out_ptr is not already at the end of the filesystem.
 		 * We also need to compute the CRC for it.
 		 */
-		 //KEN: TODO: CRC computation!
 		if (len < out->cur_out_ptr) {
 			error("attempted to pad file %llu bytes less than the current output pointer",
 					out->cur_out_ptr - len);
diff --git a/ext4_utils/simg2img.c b/ext4_utils/simg2img.c
index 9c1ad37..88c67b4 100644
--- a/ext4_utils/simg2img.c
+++ b/ext4_utils/simg2img.c
@@ -27,6 +27,7 @@
 #include "ext4_utils.h"
 #include "output_file.h"
 #include "sparse_format.h"
+#include "sparse_crc32.h"
 
 #if defined(__APPLE__) && defined(__MACH__)
 #define lseek64 lseek
@@ -36,6 +37,9 @@
 #define COPY_BUF_SIZE (1024*1024)
 u8 *copybuf;
 
+/* This will be malloc'ed with the size of blk_sz from the sparse file header */
+u8* zerobuf;
+
 #define SPARSE_HEADER_MAJOR_VER 1
 #define SPARSE_HEADER_LEN       (sizeof(sparse_header_t))
 #define CHUNK_HEADER_LEN (sizeof(chunk_header_t))
@@ -52,8 +56,15 @@
 
 	while (len) {
 		chunk = (len > COPY_BUF_SIZE) ? COPY_BUF_SIZE : len;
-		fread(copybuf, chunk, 1, in);
-		fwrite(copybuf, chunk, 1, out);
+		if (fread(copybuf, chunk, 1, in) != 1) {
+			fprintf(stderr, "fread returned an error copying a raw chunk\n");
+			exit(-1);
+		}
+		*crc32 = sparse_crc32(*crc32, copybuf, chunk);
+		if (fwrite(copybuf, chunk, 1, out) != 1) {
+			fprintf(stderr, "fwrite returned an error copying a raw chunk\n");
+			exit(-1);
+		}
 		len -= chunk;
 	}
 
@@ -67,17 +78,26 @@
 	 * as a 32 bit value of blocks.
 	 */
 	u64 len = (u64)blocks * blk_sz;
-	long skip_chunk;
+	u64 len_save;
+	u32 skip_chunk;
 
 	/* Fseek takes the offset as a long, which may be 32 bits on some systems.
 	 * So, lets do a sequence of fseeks() with SEEK_CUR to get the file pointer
 	 * where we want it.
 	 */
+	len_save = len;
 	while (len) {
 		skip_chunk = (len > 0x80000000) ? 0x80000000 : len;
 		fseek(out, skip_chunk, SEEK_CUR);
 		len -= skip_chunk;
 	}
+	/* And compute the CRC of the skipped region a chunk at a time */
+	len = len_save;
+	while (len) {
+		skip_chunk = (skip_chunk > blk_sz) ? blk_sz : skip_chunk;
+		*crc32 = sparse_crc32(*crc32, zerobuf, skip_chunk);
+		len -= skip_chunk;
+	}
 
 	return blocks;
 }
@@ -133,6 +153,11 @@
 		fseek(in, sparse_header.file_hdr_sz - SPARSE_HEADER_LEN, SEEK_CUR);
 	}
 
+	if ( (zerobuf = malloc(sparse_header.blk_sz)) == 0) {
+		fprintf(stderr, "Cannot malloc zero buf\n");
+		exit(-1);
+	}
+
 	for (i=0; i<sparse_header.total_chunks; i++) {
 		if (fread(&chunk_header, sizeof(chunk_header), 1, in) != 1) {
 			fprintf(stderr, "Error reading chunk header\n");
@@ -176,7 +201,10 @@
 	 * will make the file the correct size.  Make sure the offset is
 	 * computed in 64 bits, and the function called can handle 64 bits.
 	 */
-	ftruncate(fileno(out), (u64)total_blocks * sparse_header.blk_sz);
+	if (ftruncate(fileno(out), (u64)total_blocks * sparse_header.blk_sz)) {
+		fprintf(stderr, "Error calling ftruncate() to set the image size\n");
+		exit(-1);
+	}
 
 	fclose(in);
 	fclose(out);
@@ -188,7 +216,7 @@
 	}
 
 	if (sparse_header.image_checksum != crc32) {
-		fprintf(stderr, "computed crc32 of %d, expected %d\n",
+		fprintf(stderr, "computed crc32 of 0x%8.8x, expected 0x%8.8x\n",
 			 crc32, sparse_header.image_checksum);
 		exit(-1);
 	}
diff --git a/ext4_utils/sparse_crc32.c b/ext4_utils/sparse_crc32.c
new file mode 100644
index 0000000..9336b1d
--- /dev/null
+++ b/ext4_utils/sparse_crc32.c
@@ -0,0 +1,111 @@
+/*-
+ *  COPYRIGHT (C) 1986 Gary S. Brown.  You may use this program, or
+ *  code or tables extracted from it, as desired without restriction.
+ */
+
+/*
+ *  First, the polynomial itself and its table of feedback terms.  The
+ *  polynomial is
+ *  X^32+X^26+X^23+X^22+X^16+X^12+X^11+X^10+X^8+X^7+X^5+X^4+X^2+X^1+X^0
+ *
+ *  Note that we take it "backwards" and put the highest-order term in
+ *  the lowest-order bit.  The X^32 term is "implied"; the LSB is the
+ *  X^31 term, etc.  The X^0 term (usually shown as "+1") results in
+ *  the MSB being 1
+ *
+ *  Note that the usual hardware shift register implementation, which
+ *  is what we're using (we're merely optimizing it by doing eight-bit
+ *  chunks at a time) shifts bits into the lowest-order term.  In our
+ *  implementation, that means shifting towards the right.  Why do we
+ *  do it this way?  Because the calculated CRC must be transmitted in
+ *  order from highest-order term to lowest-order term.  UARTs transmit
+ *  characters in order from LSB to MSB.  By storing the CRC this way
+ *  we hand it to the UART in the order low-byte to high-byte; the UART
+ *  sends each low-bit to hight-bit; and the result is transmission bit
+ *  by bit from highest- to lowest-order term without requiring any bit
+ *  shuffling on our part.  Reception works similarly
+ *
+ *  The feedback terms table consists of 256, 32-bit entries.  Notes
+ *
+ *      The table can be generated at runtime if desired; code to do so
+ *      is shown later.  It might not be obvious, but the feedback
+ *      terms simply represent the results of eight shift/xor opera
+ *      tions for all combinations of data and CRC register values
+ *
+ *      The values must be right-shifted by eight bits by the "updcrc
+ *      logic; the shift must be unsigned (bring in zeroes).  On some
+ *      hardware you could probably optimize the shift in assembler by
+ *      using byte-swap instructions
+ *      polynomial $edb88320
+ *
+ *
+ * CRC32 code derived from work by Gary S. Brown.
+ */
+
+/* Code taken from FreeBSD 8 */
+#include "ext4_utils.h"
+
+static u32 crc32_tab[] = {
+        0x00000000, 0x77073096, 0xee0e612c, 0x990951ba, 0x076dc419, 0x706af48f,
+        0xe963a535, 0x9e6495a3, 0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,
+        0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91, 0x1db71064, 0x6ab020f2,
+        0xf3b97148, 0x84be41de, 0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,
+        0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec, 0x14015c4f, 0x63066cd9,
+        0xfa0f3d63, 0x8d080df5, 0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,
+        0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b, 0x35b5a8fa, 0x42b2986c,
+        0xdbbbc9d6, 0xacbcf940, 0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,
+        0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116, 0x21b4f4b5, 0x56b3c423,
+        0xcfba9599, 0xb8bda50f, 0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
+        0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d, 0x76dc4190, 0x01db7106,
+        0x98d220bc, 0xefd5102a, 0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,
+        0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818, 0x7f6a0dbb, 0x086d3d2d,
+        0x91646c97, 0xe6635c01, 0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,
+        0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457, 0x65b0d9c6, 0x12b7e950,
+        0x8bbeb8ea, 0xfcb9887c, 0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
+        0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2, 0x4adfa541, 0x3dd895d7,
+        0xa4d1c46d, 0xd3d6f4fb, 0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0,
+        0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9, 0x5005713c, 0x270241aa,
+        0xbe0b1010, 0xc90c2086, 0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
+        0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4, 0x59b33d17, 0x2eb40d81,
+        0xb7bd5c3b, 0xc0ba6cad, 0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a,
+        0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683, 0xe3630b12, 0x94643b84,
+        0x0d6d6a3e, 0x7a6a5aa8, 0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,
+        0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe, 0xf762575d, 0x806567cb,
+        0x196c3671, 0x6e6b06e7, 0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,
+        0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5, 0xd6d6a3e8, 0xa1d1937e,
+        0x38d8c2c4, 0x4fdff252, 0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
+        0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60, 0xdf60efc3, 0xa867df55,
+        0x316e8eef, 0x4669be79, 0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
+        0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f, 0xc5ba3bbe, 0xb2bd0b28,
+        0x2bb45a92, 0x5cb36a04, 0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,
+        0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a, 0x9c0906a9, 0xeb0e363f,
+        0x72076785, 0x05005713, 0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38,
+        0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21, 0x86d3d2d4, 0xf1d4e242,
+        0x68ddb3f8, 0x1fda836e, 0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
+        0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c, 0x8f659eff, 0xf862ae69,
+        0x616bffd3, 0x166ccf45, 0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2,
+        0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db, 0xaed16a4a, 0xd9d65adc,
+        0x40df0b66, 0x37d83bf0, 0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
+        0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6, 0xbad03605, 0xcdd70693,
+        0x54de5729, 0x23d967bf, 0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,
+        0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d
+};
+
+/*
+ * A function that calculates the CRC-32 based on the table above is
+ * given below for documentation purposes. An equivalent implementation
+ * of this function that's actually used in the kernel can be found
+ * in sys/libkern.h, where it can be inlined.
+ */
+
+u32 sparse_crc32(u32 crc_in, const void *buf, int size)
+{
+        const u8 *p = buf;
+        u32 crc;
+
+        crc = crc_in ^ ~0U;
+        while (size--)
+                crc = crc32_tab[(crc ^ *p++) & 0xFF] ^ (crc >> 8);
+        return crc ^ ~0U;
+}
+
diff --git a/ext4_utils/sparse_crc32.h b/ext4_utils/sparse_crc32.h
new file mode 100644
index 0000000..21625ba
--- /dev/null
+++ b/ext4_utils/sparse_crc32.h
@@ -0,0 +1,18 @@
+/*
+ * Copyright (C) 2010 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.
+ */
+
+u32 sparse_crc32(u32 crc, const void *buf, size_t size);
+