diff --git a/README.md b/README.md
index dd2c7f0..37adf34 100644
--- a/README.md
+++ b/README.md
@@ -1,2 +1,13 @@
 # dsk2woz
-A tool to convert Apple II DSK images to WOZ format
+A command-line tool to convert Apple II DSK images to WOZ format.
+
+Usage:
+
+    dsk2woz input.dsk output.woz
+
+Reads the contents of the DOS 3.3 disk input.dsk and outputs the WOZ-format file output.woz.
+
+## Building
+There are no dependencies beyond the C standard library. So e.g.
+
+    cc dsk2woz.c -o dsk2woz
diff --git a/dsk2woz.c b/dsk2woz.c
new file mode 100644
index 0000000..cd2c58a
--- /dev/null
+++ b/dsk2woz.c
@@ -0,0 +1,358 @@
+#include <assert.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+
+static uint32_t crc32(const uint8_t *buf, size_t size);
+static void serialise_track(uint8_t *dest, const uint8_t *src, uint8_t track_number);
+
+int main(int argc, char *argv[]) {
+	// Announce failure if there are anything other than three arguments.
+	if(argc != 3) {
+		printf("USAGE: dsk2woz input.dsk output.woz\n");
+		return -1;
+	}
+
+	// Attempt to read the standard DSK number of bytes into a buffer.
+	FILE *const dsk_file = fopen(argv[1], "rb");
+	if(!dsk_file) {
+		printf("ERROR: could not open %s for reading\n", argv[1]);
+		return -2;
+	}
+	const size_t dsk_image_size = 35 * 16 * 256;
+	uint8_t dsk[dsk_image_size];
+	const size_t bytes_read = fread(dsk, 1, dsk_image_size, dsk_file);
+	fclose(dsk_file);
+
+	// If the DSK image was too short, announce failure. Some DSK files
+	// seem empirically to be too long, but it's unclear that the extra
+	// bytes actually mean anything — they're usually not many.
+	if(bytes_read != dsk_image_size) {
+		printf("ERROR: DSK image too small\n");
+		return -3;
+	}
+
+	// Create a buffer for the portion of the WOZ image that comes after
+	// the 12-byte header. The header will house the CRC, which will be
+	// calculated later.
+	const size_t woz_image_size = 256 + 35*6656;
+	uint8_t woz[woz_image_size];
+#define set_int32(location, value)	\
+	woz[location] = (value) & 0xff;	\
+	woz[location+1] = ((value) >> 8) & 0xff;	\
+	woz[location+2] = ((value) >> 16) & 0xff;	\
+	woz[location+3] = (value) >> 24;
+
+
+
+	/*
+		WOZ image item 1: an INFO chunk.
+	*/
+	strcpy((char *)&woz[0], "INFO");	// Chunk ID.
+	set_int32(4, 60);					// Chunk size.
+	woz[8] = 1;							// INFO version: 1.
+	woz[9] = 1;							// Disk type: 5.25".
+	woz[10] = 0;						// Write protection: disabled.
+	woz[11] = 0;						// Cross-track synchronised image: no.
+	woz[12] = 1;						// MC3470 fake bits have been removed: yes.
+										// (or, rather, were never inserted)
+															
+	// Append creator, which needs to be padded out to 32
+	// bytes with space characters.
+	const char creator[] = "dsk2woz 1.0";
+	const size_t creator_length = strlen(creator);
+	assert(creator_length < 32);
+
+	strcpy((char *)&woz[13], creator);
+	memset(&woz[13 + strlen(creator)], 32 - strlen(creator), ' ');
+
+	// Chunk should be padded with 0s to reach 60 bytes in length.
+	memset(&woz[13 + 32], (8+60) - (13 + 32), 0);
+
+
+
+	/*
+		WOZ image item 2: a TMAP chunk.
+	*/
+	strcpy((char *)&woz[68], "TMAP");		// Chunk ID.
+	set_int32(72, 160);						// Chunk size.
+
+	// This is a DSK conversion, so the TMAP table is just the next
+	// track in every fourth slot, with 255s in between.
+	for(int c = 0; c < 35; ++c) {
+		woz[76 + (c << 2)] = c;
+		woz[77 + (c << 2)] = woz[78 + (c << 2)] = woz[79 + (c << 2)] = 255;
+	}
+
+	// So there are 20 track slots that a DSK doesn't reach; set them
+	// to no-track-mapped.
+	memset(&woz[76 + (35 << 2)], 20, 0xff);
+
+
+
+	/*
+		WOZ image item 3: a TRKS chunk.
+	*/
+	strcpy((char *)&woz[236], "TRKS");	// Chunk ID.
+	set_int32(240, 35*65536);			// Chunk size.
+
+	// The output pointer holds a **bit** position into the WOZ buffer.
+	size_t output_pointer = 244;
+
+	// Write out all 35 tracks.
+	for(int c = 0; c < 35; ++c) {
+		serialise_track(&woz[output_pointer], &dsk[c * 16 * 256], c);
+		output_pointer += 6656;
+	}
+	#undef set_int32
+
+
+
+	/*
+		WOZ image output.
+	*/
+	FILE *const woz_file = fopen(argv[2], "wb");
+	if(!woz_file) {
+		printf("ERROR: Could not open %s for writing\n", argv[2]);
+		return -5;
+	}
+	fputs("WOZ1", woz_file);
+	fputc(0xff, woz_file);
+	fputs("\n\r\n", woz_file);
+
+	const uint32_t crc = crc32(woz, sizeof(woz));
+	fputc(crc & 0xff, woz_file);
+	fputc((crc >> 8) & 0xff, woz_file);
+	fputc((crc >> 16) & 0xff, woz_file);
+	fputc(crc >> 24, woz_file);
+
+	const size_t length_written = fwrite(woz, 1, sizeof(woz), woz_file);
+	fclose(woz_file);
+
+	if(length_written != sizeof(woz)) {
+		printf("ERROR: Could not write full WOZ image\n");
+		return -6;
+	}
+
+	return 0;
+}
+
+
+
+/*
+	CRC generator. Essentially that of Gary S. Brown from 1986, but I've
+	fixed the initial value. This is exactly the code advocated by the
+	WOZ file specifications (with some extra consts).
+*/
+static const uint32_t 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
+};
+
+uint32_t crc32(const uint8_t *buf, size_t size) {
+	uint32_t crc = ~0;
+	size_t byte = 0;
+	while (size--) {
+		crc = crc32_tab[(crc ^ buf[byte]) & 0xFF] ^ (crc >> 8);
+		++byte;
+	}
+	return ~crc;
+}
+
+
+
+/*
+	DSK sector serialiser. Constructs the 6-and-2 DOS 3.3-style on-disk
+	representation of a DOS logical-order sector dump.
+*/
+static size_t write_bit(uint8_t *buffer, size_t position, int value) {
+	buffer[position >> 3] |= (value ? 0x80 : 0x00) >> (position & 7);
+	return position + 1;
+}
+
+static size_t write_byte(uint8_t *buffer, size_t position, int value) {
+	int mask = 0x80;
+	while(mask) {
+		position = write_bit(buffer, position, value & mask);
+		mask >>= 1;
+	}
+	return position;
+}
+
+static size_t write_4_and_4(uint8_t *buffer, size_t position, int value) {
+	position = write_byte(buffer, position, (value >> 1) | 0xaa);
+	position = write_byte(buffer, position, value | 0xaa);
+	return position;
+}
+
+static size_t write_sync(uint8_t *buffer, size_t position) {
+	position = write_byte(buffer, position, 0xff);
+	position = write_bit(buffer, position, 0);
+	position = write_bit(buffer, position, 0);
+	return position;
+}
+
+static void encode_6_and_2(uint8_t *dest, const uint8_t *src) {
+	const uint8_t six_and_two_mapping[] = {
+		0x96, 0x97, 0x9a, 0x9b, 0x9d, 0x9e, 0x9f, 0xa6,
+		0xa7, 0xab, 0xac, 0xad, 0xae, 0xaf, 0xb2, 0xb3,
+		0xb4, 0xb5, 0xb6, 0xb7, 0xb9, 0xba, 0xbb, 0xbc,
+		0xbd, 0xbe, 0xbf, 0xcb, 0xcd, 0xce, 0xcf, 0xd3,
+		0xd6, 0xd7, 0xd9, 0xda, 0xdb, 0xdc, 0xdd, 0xde,
+		0xdf, 0xe5, 0xe6, 0xe7, 0xe9, 0xea, 0xeb, 0xec,
+		0xed, 0xee, 0xef, 0xf2, 0xf3, 0xf4, 0xf5, 0xf6,
+		0xf7, 0xf9, 0xfa, 0xfb, 0xfc, 0xfd, 0xfe, 0xff
+	};
+
+	// Fill in byte values: the first 86 bytes contain shuffled
+	// and combined copies of the bottom two bits of the sector
+	// contents; the 256 bytes afterwards are the remaining
+	// six bits.
+	const uint8_t bit_reverse[] = {0, 2, 1, 3};
+	for(size_t c = 0; c < 84; ++c) {
+		dest[c] =
+			bit_reverse[src[c]&3] |
+			(bit_reverse[src[c + 86]&3] << 2) |
+			(bit_reverse[src[c + 172]&3] << 4);
+	}
+	dest[84] =
+		(bit_reverse[src[84]&3] << 0) |
+		(bit_reverse[src[170]&3] << 2);
+	dest[85] =
+		(bit_reverse[src[85]&3] << 0) |
+		(bit_reverse[src[171]&3] << 2);
+
+	for(size_t c = 0; c < 256; ++c) {
+		dest[86 + c] = src[c] >> 2;
+	}
+
+	// Exclusive OR each byte with the one before it.
+	dest[342] = dest[341];
+	size_t location = 342;
+	while(location) {
+		--location;
+		dest[location] ^= dest[location-1];
+	}
+
+	// Map six-bit values up to full bytes.
+	for(size_t c = 0; c < 343; ++c) {
+		dest[c] = six_and_two_mapping[dest[c]];
+	}
+
+}
+
+void serialise_track(uint8_t *dest, const uint8_t *src, uint8_t track_number) {
+	size_t track_position = 0;	// This is the track position **in bits**.
+	memset(dest, 0, 6646);
+
+	// Step through the physical sector.
+	for(int sector = 0; sector < 16; ++sector) {
+		/*
+			Write the sector header.
+		*/
+
+		// Lead-in.
+		for(int c = 0; c < 10; ++c) {
+			track_position = write_sync(dest, track_position);
+		}
+
+		// Prologue.
+		track_position = write_byte(dest, track_position, 0xd5);
+		track_position = write_byte(dest, track_position, 0xaa);
+		track_position = write_byte(dest, track_position, 0x96);
+
+		// Volume, track, setor and checksum, all in 4-and-4 format.
+		track_position = write_4_and_4(dest, track_position, 254);
+		track_position = write_4_and_4(dest, track_position, track_number);
+		track_position = write_4_and_4(dest, track_position, sector);
+		track_position = write_4_and_4(dest, track_position, 254 ^ track_number ^ sector);
+
+		// Epilogue.
+		track_position = write_byte(dest, track_position, 0xde);
+		track_position = write_byte(dest, track_position, 0xaa);
+		track_position = write_byte(dest, track_position, 0xeb);
+
+
+
+		/*
+			Write the sector body.
+		*/
+		// Lead-in.
+		for(int c = 0; c < 10; ++c) {
+			track_position = write_sync(dest, track_position);
+		}
+
+		// Prologue.
+		track_position = write_byte(dest, track_position, 0xd5);
+		track_position = write_byte(dest, track_position, 0xaa);
+		track_position = write_byte(dest, track_position, 0xad);
+
+		// Map from this physical sector to a logical sector.
+		const int logical_sector = (sector == 15) ? 15 : ((sector * 7) % 15);
+
+		// Sector contents
+		uint8_t contents[343];
+		encode_6_and_2(contents, &src[logical_sector * 256]);
+		for(size_t c = 0; c < sizeof(contents); ++c) {
+			track_position = write_byte(dest, track_position, contents[c]);			
+		}
+
+		// Epilogue.
+		track_position = write_byte(dest, track_position, 0xde);
+		track_position = write_byte(dest, track_position, 0xaa);
+		track_position = write_byte(dest, track_position, 0xeb);
+	}
+	
+	// Pad out to roughly 50,000 bits.
+	while(track_position < 50000) {
+		track_position = write_sync(dest, track_position);
+	}
+
+	// Add the track suffix.
+	dest[6646] = (track_position >> 3) & 0xff;
+	dest[6647] = (track_position >> 11) & 0xff;	// Byte count.
+	dest[6648] = track_position & 0xff;
+	dest[6649] = (track_position >> 8) & 0xff;	// Bit count.
+	dest[6650] =  dest[6651] = 0xff;			// Splice information: none.
+}