// license:BSD-3-Clause
// copyright-holders:Nathan Woods, R. Belmont
/*********************************************************************

    ap_dsk35.c

    Apple 3.5" disk images

    This code supports 3.5" 400k/800k disks used in early Macintoshes
    and the Apple IIgs, and 3.5" 1440k MFM disks used on most Macintoshes.

    These disks have the following properties:

        400k:   80 tracks, 1 head
        800k:   80 tracks, 2 heads

        Tracks  0-15 have 12 sectors each
        Tracks 16-31 have 11 sectors each
        Tracks 32-47 have 10 sectors each
        Tracks 48-63 have  9 sectors each
        Tracks 64-79 have  8 sectors each

        1440k disks are simply 80 tracks, 2 heads and 18 sectors per track.

    Each sector on 400/800k disks has 524 bytes, 512 of which are really used by the Macintosh

    (80 tracks) * (avg of 10 sectors) * (512 bytes) * (2 sides) = 800 kB

    Data is nibblized : 3 data bytes -> 4 bytes on disk.

    In addition to 512 logical bytes, each sector contains 800 physical
    bytes.  Here is the layout of the physical sector:

        Pos
        0       0xFF (pad byte where head is turned on ???)
        1-35    self synch 0xFFs (7*5) (42 bytes actually written to media)
        36      0xD5
        37      0xAA
        38      0x96
        39      diskbytes[(track number) & 0x3F]
        40      diskbytes[(sector number)]
        41      diskbytes[("side")]
        42      diskbytes[("format byte")]
        43      diskbytes[("sum")]
        44      0xDE
        45      0xAA
        46      pad byte where head is turned off/on (0xFF here)
        47-51   self synch 0xFFs (6 bytes actually written to media)
        52      0xD5
        53      0xAA
        54      0xAD
        55      spare byte, generally diskbytes[(sector number)]
        56-754  "nibblized" sector data ...
        755-758 checksum
        759     0xDE
        760     0xAA
        761     pad byte where head is turned off (0xFF here)

    MFM Track layout for 1440K disks:
        Pos
    --------- track ID
    0   0x4E (x80)
    80  00 (x12)
    92  C2 (x3) Mark byte
    93  FC Index mark
    94  4E (x50)
    --------- sector ID
    144 00 (x12)
    156 A1 (x3) Mark byte
    159 FE Address mark
    160 xx Track number
    161 xx Side number
    162 xx Sector number
    163 xx Sector length
    164/165 xx CRC
    166 4E (x22)
    --------- sector data
    188 00 (x12)
    200 A1 (x3) Mark byte
    203 FB Data address mark
    204 xx (x256) data
    460 4E (x54)
    (repeat from sector ID to fill track; end of track is padded with 4E)

    Note : "Self synch refers to a technique whereby two zeroes are inserted
    between each synch byte written to the disk.", i.e. "0xFF, 0xFF, 0xFF,
    0xFF, 0xFF" is actually "0xFF, 0x3F, 0xCF, 0xF3, 0xFC, 0xFF" on disk.
    Since the IWM assumes the data transfer is complete when the MSBit of its
    shift register is 1, we do read 4 0xFF, even though they are not
    contiguous on the disk media.  Some reflexion shows that 4 synch bytes
    allow the IWM to synchronize with the trailing data.

    Format byte codes:
        0x00    Apple II
        0x01    Lisa
        0x02    Mac MFS (single sided)?
        0x22    Mac MFS (double sided)?

*********************************************************************/

#include <stdio.h>
#include <assert.h>

#include "emu.h" // logerror
#include "ap_dsk35.h"

struct apple35_tag
{
	uint32_t data_offset;
	uint32_t data_size;
	uint8_t format_byte;
	uint8_t sides;
	unsigned int is_1440k : 1;

	/* stuff used in DiskCopy images */
	uint32_t tag_offset;
	uint32_t tag_size;
};



/* normal number of sector for each track */
static const uint8_t apple35_tracklen_800kb[80] =
{
	12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12,
	11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11,
	10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10,
		9,  9,  9,  9,  9,  9,  9,  9,  9,  9,  9,  9,  9,  9,  9,  9,
		8,  8,  8,  8,  8,  8,  8,  8,  8,  8,  8,  8,  8,  8,  8,  8
};

/* blocks of data used to nibblize tracks */
static const uint8_t diskbytes[] =
{
	0x96, 0x97, 0x9A, 0x9B,  0x9D, 0x9E, 0x9F, 0xA6, /* 0x00 */
	0xA7, 0xAB, 0xAC, 0xAD,  0xAE, 0xAF, 0xB2, 0xB3,
	0xB4, 0xB5, 0xB6, 0xB7,  0xB9, 0xBA, 0xBB, 0xBC, /* 0x10 */
	0xBD, 0xBE, 0xBF, 0xCB,  0xCD, 0xCE, 0xCF, 0xD3,
	0xD6, 0xD7, 0xD9, 0xDA,  0xDB, 0xDC, 0xDD, 0xDE, /* 0x20 */
	0xDF, 0xE5, 0xE6, 0xE7,  0xE9, 0xEA, 0xEB, 0xEC,
	0xED, 0xEE, 0xEF, 0xF2,  0xF3, 0xF4, 0xF5, 0xF6, /* 0x30 */
	0xF7, 0xF9, 0xFA, 0xFB,  0xFC, 0xFD, 0xFE, 0xFF
};

/* reverse lookup of diskbytes */
static const int16_t rev_diskbytes[] =
{
	-1,   -1,   -1,   -1,    -1,   -1,   -1,   -1,   /* 0x00 */
	-1,   -1,   -1,   -1,    -1,   -1,   -1,   -1,
	-1,   -1,   -1,   -1,    -1,   -1,   -1,   -1,   /* 0x10 */
	-1,   -1,   -1,   -1,    -1,   -1,   -1,   -1,
	-1,   -1,   -1,   -1,    -1,   -1,   -1,   -1,   /* 0x20 */
	-1,   -1,   -1,   -1,    -1,   -1,   -1,   -1,
	-1,   -1,   -1,   -1,    -1,   -1,   -1,   -1,   /* 0x30 */
	-1,   -1,   -1,   -1,    -1,   -1,   -1,   -1,
	-1,   -1,   -1,   -1,    -1,   -1,   -1,   -1,   /* 0x40 */
	-1,   -1,   -1,   -1,    -1,   -1,   -1,   -1,
	-1,   -1,   -1,   -1,    -1,   -1,   -1,   -1,   /* 0x50 */
	-1,   -1,   -1,   -1,    -1,   -1,   -1,   -1,
	-1,   -1,   -1,   -1,    -1,   -1,   -1,   -1,   /* 0x60 */
	-1,   -1,   -1,   -1,    -1,   -1,   -1,   -1,
	-1,   -1,   -1,   -1,    -1,   -1,   -1,   -1,   /* 0x70 */
	-1,   -1,   -1,   -1,    -1,   -1,   -1,   -1,
	-1,   -1,   -1,   -1,    -1,   -1,   -1,   -1,   /* 0x80 */
	-1,   -1,   -1,   -1,    -1,   -1,   -1,   -1,
	-1,   -1,   -1,   -1,    -1,   -1,   0x00, 0x01, /* 0x90 */
	-1,   -1,   0x02, 0x03,  -1,   0x04, 0x05, 0x06,
	-1,   -1,   -1,   -1,    -1,   -1,   0x07, 0x08, /* 0xA0 */
	-1,   -1,   -1,   0x09,  0x0A, 0x0B, 0x0C, 0x0D,
	-1,   -1,   0x0E, 0x0F,  0x10, 0x11, 0x12, 0x13, /* 0xB0 */
	-1,   0x14, 0x15, 0x16,  0x17, 0x18, 0x19, 0x1A,
	-1,   -1,   -1,   -1,    -1,   -1,   -1,   -1,   /* 0xC0 */
	-1,   -1,   -1,   0x1B,  -1,   0x1C, 0x1D, 0x1E,
	-1,   -1,   -1,   0x1F,  -1,   -1,   0x20, 0x21, /* 0xD0 */
	-1,   0x22, 0x23, 0x24,  0x25, 0x26, 0x27, 0x28,
	-1,   -1,   -1,   -1,    -1,   0x29, 0x2A, 0x2B, /* 0xE0 */
	-1,   0x2C, 0x2D, 0x2E,  0x2F, 0x30, 0x31, 0x32,
	-1,   -1,   0x33, 0x34,  0x35, 0x36, 0x37, 0x38, /* 0xF0 */
	-1,   0x39, 0x3A, 0x3B,  0x3C, 0x3D, 0x3E, 0x3F
};

static const uint8_t blk1[] =
{
	/*0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
	0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
	0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
	0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
	0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
	0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
	0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
	0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF,
	0xFF, 0xFF, 0xD5, 0xAA, 0x96*/
	0xFF,
	0xFF, 0x3F, 0xCF, 0xF3, 0xFC, 0xFF,
	0xFF, 0x3F, 0xCF, 0xF3, 0xFC, 0xFF,
	0xFF, 0x3F, 0xCF, 0xF3, 0xFC, 0xFF,
	0xFF, 0x3F, 0xCF, 0xF3, 0xFC, 0xFF,
	0xFF, 0x3F, 0xCF, 0xF3, 0xFC, 0xFF,
	0xFF, 0x3F, 0xCF, 0xF3, 0xFC, 0xFF,
	0xFF, 0x3F, 0xCF, 0xF3, 0xFC, 0xFF,
	0xD5, 0xAA, 0x96
};
static const uint8_t blk2[] =
{
	0xDE, 0xAA, 0xFF, 0xFF, 0x3F, 0xCF, 0xF3, 0xFC, 0xFF, 0xD5, 0xAA, 0xAD
};
static const uint8_t blk3[] =
{
	0xDE, 0xAA, 0xFF
};



static struct apple35_tag *get_apple35_tag(floppy_image_legacy *floppy)
{
	struct apple35_tag *tag;
	tag = (struct apple35_tag *) floppy_tag(floppy);
	return tag;
}



int apple35_sectors_per_track(floppy_image_legacy *image, int track)
{
	int sectors;

	assert(track >= 0);
	assert(track < ARRAY_LENGTH(apple35_tracklen_800kb));

	if (get_apple35_tag(image)->is_1440k)
		sectors = 18;
	else
		sectors = apple35_tracklen_800kb[track];
	return sectors;
}



/*
    converts data to its nibblized representation, and generate checksum

    now handles 524-byte-long sectors

    tag data IS important, since it allows data recovery when the catalog is trashed
*/
static void sony_nibblize35(const uint8_t *in, uint8_t *nib_ptr, uint8_t *csum)
{
	int i, j;
	uint32_t c1, c2, c3, c4;
	uint8_t val;
	uint8_t w1, w2, w3, w4;
	uint8_t b1[175], b2[175], b3[175];

	/* Copy from the user's buffer to our buffer, while computing
	 * the three-byte data checksum
	 */

	i = 0;
	j = 0;
	c1 = 0;
	c2 = 0;
	c3 = 0;
	while (1)
	{
		c1 = (c1 & 0xFF) << 1;
		if (c1 & 0x0100)
			c1++;

		val = in[i++];
		c3 += val;
		if (c1 & 0x0100)
		{
			c3++;
			c1 &= 0xFF;
		}
		b1[j] = (val ^ c1) & 0xFF;

		val = in[i++];
		c2 += val;
		if (c3 > 0xFF)
		{
			c2++;
			c3 &= 0xFF;
		}
		b2[j] = (val ^ c3) & 0xFF;

		if (i == 524) break;

		val = in[i++];
		c1 += val;
		if (c2 > 0xFF)
		{
			c1++;
			c2 &= 0xFF;
		}
		b3[j] = (val ^ c2) & 0xFF;
		j++;
	}
	c4 =  ((c1 & 0xC0) >> 6) | ((c2 & 0xC0) >> 4) | ((c3 & 0xC0) >> 2);
	b3[174] = 0;

	j = 0;
	for (i = 0; i <= 174; i++)
	{
		w1 = b1[i] & 0x3F;
		w2 = b2[i] & 0x3F;
		w3 = b3[i] & 0x3F;
		w4 =  ((b1[i] & 0xC0) >> 2);
		w4 |= ((b2[i] & 0xC0) >> 4);
		w4 |= ((b3[i] & 0xC0) >> 6);

		nib_ptr[j++] = w4;
		nib_ptr[j++] = w1;
		nib_ptr[j++] = w2;

		if (i != 174) nib_ptr[j++] = w3;
	}

	csum[0] = c1 & 0x3F;
	csum[1] = c2 & 0x3F;
	csum[2] = c3 & 0x3F;
	csum[3] = c4 & 0x3F;
}



/*
    does the reverse process of sony_nibblize35
*/
static void sony_denibblize35(uint8_t *out, const uint8_t *nib_ptr, uint8_t *checksum)
{
	int i, j;
	uint32_t c1,c2,c3,c4;
	uint8_t val;
	uint8_t w1,w2,w3=0,w4;
	uint8_t b1[175],b2[175],b3[175];

	j = 0;
	for (i=0; i<=174; i++)
	{
		w4 = nib_ptr[j++];
		w1 = nib_ptr[j++];
		w2 = nib_ptr[j++];

		if (i != 174) w3 = nib_ptr[j++];

		b1[i] = (w1 & 0x3F) | ((w4 << 2) & 0xC0);
		b2[i] = (w2 & 0x3F) | ((w4 << 4) & 0xC0);
		b3[i] = (w3 & 0x3F) | ((w4 << 6) & 0xC0);
	}

	/* Copy from the user's buffer to our buffer, while computing
	 * the three-byte data checksum
	 */

	i = 0;
	j = 0;
	c1 = 0;
	c2 = 0;
	c3 = 0;
	while (1)
	{
		c1 = (c1 & 0xFF) << 1;
		if (c1 & 0x0100)
			c1++;

		val = (b1[j] ^ c1) & 0xFF;
		c3 += val;
		if (c1 & 0x0100)
		{
			c3++;
			c1 &= 0xFF;
		}
		out[i++] = val;

		val = (b2[j] ^ c3) & 0xFF;
		c2 += val;
		if (c3 > 0xFF)
		{
			c2++;
			c3 &= 0xFF;
		}
		out[i++] = val;

		if (i == 524) break;

		val = (b3[j] ^ c2) & 0xFF;
		c1 += val;
		if (c2 > 0xFF)
		{
			c1++;
			c2 &= 0xFF;
		}
		out[i++] = val;
		j++;
	}
	c4 =  ((c1 & 0xC0) >> 6) | ((c2 & 0xC0) >> 4) | ((c3 & 0xC0) >> 2);
	b3[174] = 0;

	checksum[0] = c1 & 0x3F;
	checksum[1] = c2 & 0x3F;
	checksum[2] = c3 & 0x3F;
	checksum[3] = c4 & 0x3F;
}



void sony_filltrack(uint8_t *buffer, size_t buffer_len, size_t *pos, uint8_t data)
{
	buffer[*pos / 8] &= 0xFF << (8 - (*pos % 8));
	buffer[*pos / 8] |= data >> (*pos % 8);

	*pos += 8;
	*pos %= buffer_len * 8;

	buffer[*pos / 8] &= 0xFF >> (*pos % 8);
	buffer[*pos / 8] |= data << (8 - (*pos % 8));
}



uint8_t sony_fetchtrack(const uint8_t *buffer, size_t buffer_len, size_t *pos)
{
	uint8_t data;

	data = buffer[*pos / 8] << (*pos % 8);
	*pos += 8;
	*pos %= (buffer_len * 8);
	data |= buffer[*pos / 8] >> (8 - (*pos % 8));

	while ((data & 0x80) == 0)
	{
		/* this code looks weird because it isn't simply rotating the new bit
		 * in, but for some reason it won't work if I rotate the bit in; I
		 * have to match the algorithm used by the old code */
		data <<= 1;
		data |= (buffer[*pos / 8] >> (8 - ((*pos % 8) + 1)));
		(*pos)++;
		*pos %= (buffer_len * 8);
	}

//    printf("sony_fetchtrack: pos %ld = %02x\n", *pos/8, data);

	return data;
}



static uint32_t apple35_get_offset(floppy_image_legacy *floppy, int head, int track, int sector, uint32_t *tag_offset)
{
	int i;
	uint32_t sector_index = 0;
	struct apple35_tag *tag;

	tag = get_apple35_tag(floppy);

	if (track >= ARRAY_LENGTH(apple35_tracklen_800kb))
		return ~0;
	if (head >= tag->sides)
		return ~0;
	if (sector >= apple35_sectors_per_track(floppy, track))
		return ~0;

	for (i = 0; i < track; i++)
		sector_index += apple35_sectors_per_track(floppy, i);
	sector_index *= tag->sides;
	if (head)
		sector_index += apple35_sectors_per_track(floppy, i);
	sector_index += sector;

	if (tag_offset)
	{
		*tag_offset = sector_index * 12;
		if (*tag_offset >= tag->tag_size)
		{
			*tag_offset = ~0;
		}
		else
		{
			*tag_offset += tag->tag_offset;
		}
	}
	return sector_index * 0x200 + tag->data_offset;
}



static floperr_t apple35_read_sector(floppy_image_legacy *floppy, int head, int track, int sector, void *buffer, size_t buflen)
{
	uint32_t data_offset;
	data_offset = apple35_get_offset(floppy, head, track, sector, nullptr);
	if (data_offset == ~0)
	{
		return FLOPPY_ERROR_SEEKERROR;
	}
	floppy_image_read(floppy, buffer, data_offset, buflen);
	return FLOPPY_ERROR_SUCCESS;
}



static floperr_t apple35_write_sector(floppy_image_legacy *floppy, int head, int track, int sector, const void *buffer, size_t buflen, int ddam)
{
	uint32_t data_offset;

	data_offset = apple35_get_offset(floppy, head, track, sector, nullptr);
	if (data_offset == ~0)
		return FLOPPY_ERROR_SEEKERROR;
	floppy_image_write(floppy, buffer, data_offset, buflen);
	return FLOPPY_ERROR_SUCCESS;
}



static floperr_t apple35_read_sector_td(floppy_image_legacy *floppy, int head, int track, int sector, void *buffer, size_t buflen)
{
	floperr_t err;
	uint32_t tag_offset = 0;

	assert(buflen == 524);

	/* first read the sector */
	err = apple35_read_sector(floppy, head, track, sector, ((uint8_t *) buffer) + 12, 512);
	if (err)
	{
		return err;
	}

	/* read the tag data, if possible */
	memset(buffer, '\0', 12);
	apple35_get_offset(floppy, head, track, sector, &tag_offset);
	if (tag_offset != ~0)
	{
		floppy_image_read(floppy, buffer, tag_offset, 12);
	}

	return FLOPPY_ERROR_SUCCESS;
}



static floperr_t apple35_write_sector_td(floppy_image_legacy *floppy, int head, int track, int sector, const void *buffer, size_t buflen, int ddam)
{
	floperr_t err;
	uint32_t tag_offset = 0;

	assert(buflen == 524);

	/* first write the sector */
	err = apple35_write_sector(floppy, head, track, sector, ((const uint8_t *) buffer) + 12, 512, 0);
	if (err)
		return err;

	/* write the tag data, if possible */
	apple35_get_offset(floppy, head, track, sector, &tag_offset);
	if (tag_offset != ~0)
		floppy_image_write(floppy, buffer, tag_offset, 12);

	return FLOPPY_ERROR_SUCCESS;
}



static floperr_t apple35_get_sector_length(floppy_image_legacy *floppy, int head, int track, int sector, uint32_t *sector_length)
{
	*sector_length = 512;
	return FLOPPY_ERROR_SUCCESS;
}



static int apple35_get_heads_per_disk(floppy_image_legacy *floppy)
{
	return get_apple35_tag(floppy)->sides;
}



static int apple35_get_tracks_per_disk(floppy_image_legacy *floppy)
{
	return 80;
}



static uint32_t apple35_get_track_size(floppy_image_legacy *floppy, int head, int track)
{
	if ((track < 0) || (track >= 80))
		return 0;
	return apple35_sectors_per_track(floppy, track) * 800;
}



static uint8_t calculate_side(int head, int track)
{
	uint8_t side;
	side = head ? 0x20 : 0x00;
	if (track & 0x40)
		side |= 0x01;
	return side;
}



static floperr_t apple35_read_track(floppy_image_legacy *floppy, int head, int track, uint64_t offset, void *buffer, size_t buflen)
{
	floperr_t err;
	size_t pos = 0;
	int sector_count, sector, i;
	uint8_t sum, side;
	struct apple35_tag *tag;
	uint8_t sector_data[524];
	uint8_t nibble_data[699];
	uint8_t checksum[4];

	tag = get_apple35_tag(floppy);

	if (track >= ARRAY_LENGTH(apple35_tracklen_800kb))
		return FLOPPY_ERROR_SEEKERROR;
	if (offset != 0)
		return FLOPPY_ERROR_UNSUPPORTED;

	memset(buffer, 0xFF, buflen);
	sector_count = apple35_sectors_per_track(floppy, track);
	side = calculate_side(head, track);

	for (sector = 0; sector < sector_count; sector++)
	{
		/* read the sector */
		err = apple35_read_sector_td(floppy, head, track, sector, sector_data, ARRAY_LENGTH(sector_data));
		if (err)
		{
			return err;
		}

		sony_nibblize35(sector_data, nibble_data, checksum);

		for (i = 0; i < ARRAY_LENGTH(blk1); i++)
			sony_filltrack((uint8_t*)buffer, buflen, &pos, blk1[i]);

		sum = (track ^ sector ^ side ^ tag->format_byte) & 0x3F;

		sony_filltrack((uint8_t*)buffer, buflen, &pos, diskbytes[track & 0x3f]);
		sony_filltrack((uint8_t*)buffer, buflen, &pos, diskbytes[sector]);
		sony_filltrack((uint8_t*)buffer, buflen, &pos, diskbytes[side]);
		sony_filltrack((uint8_t*)buffer, buflen, &pos, diskbytes[tag->format_byte]);
		sony_filltrack((uint8_t*)buffer, buflen, &pos, diskbytes[sum]);

		for (i = 0; i < ARRAY_LENGTH(blk2); i++)
			sony_filltrack((uint8_t*)buffer, buflen, &pos, blk2[i]);

		sony_filltrack((uint8_t*)buffer, buflen, &pos, diskbytes[sector]);

		for (i = 0; i < ARRAY_LENGTH(nibble_data); i++)
			sony_filltrack((uint8_t*)buffer, buflen, &pos, diskbytes[nibble_data[i]]);

		for (i = 3; i >= 0; i--)
			sony_filltrack((uint8_t*)buffer, buflen, &pos, diskbytes[checksum[i]]);

		for (i = 0; i < ARRAY_LENGTH(blk3); i++)
			sony_filltrack((uint8_t*)buffer, buflen, &pos, blk3[i]);
	}

	return FLOPPY_ERROR_SUCCESS;
}



static floperr_t apple35_write_track(floppy_image_legacy *floppy, int head, int track, uint64_t offset, const void *buffer, size_t buflen)
{
	floperr_t err;
	size_t pos = 0;
	int sector_count, sector, i, j;
	struct apple35_tag *tag;
	uint8_t sum, format_byte, val, side;
	uint32_t found_sectors = 0;
	uint8_t sector_data[524];
	uint8_t nibble_data[699];
	uint8_t checksum[4];

	tag = get_apple35_tag(floppy);

	if (track >= ARRAY_LENGTH(apple35_tracklen_800kb))
		return FLOPPY_ERROR_SEEKERROR;
	if (offset != 0)
		return FLOPPY_ERROR_UNSUPPORTED;

	sector_count = apple35_sectors_per_track(floppy, track);
	side = calculate_side(head, track);

	/* do 2 rotations, in case the bit slip stuff prevent us to read the first sector */
	for (j = 0; j < (buflen * 2); j++)
	{
		if (sony_fetchtrack((uint8_t*)buffer, buflen, &pos) != 0xD5)
			continue;
		j++;

		if (sony_fetchtrack((uint8_t*)buffer, buflen, &pos) != 0xAA)
			continue;
		j++;

		if (sony_fetchtrack((uint8_t*)buffer, buflen, &pos) != 0x96)
			continue;
		j++;

		if (rev_diskbytes[sony_fetchtrack((uint8_t*)buffer, buflen, &pos)] != (track & 0x3F))
			continue;
		j++;

		sector = rev_diskbytes[sony_fetchtrack((uint8_t*)buffer, buflen, &pos)];
		if ((sector < 0) || (sector >= sector_count))
			continue;
		j++;

		if (rev_diskbytes[sony_fetchtrack((uint8_t*)buffer, buflen, &pos)] != side)
			continue;
		j++;

		format_byte = rev_diskbytes[sony_fetchtrack((uint8_t*)buffer, buflen, &pos)];
		if (format_byte != tag->format_byte)
		{
			/* this is an error, but not THAT critical, I guess */
		}
		j++;

		sum = track ^ sector ^ side ^ format_byte;
		if (rev_diskbytes[sony_fetchtrack((uint8_t*)buffer, buflen, &pos)] != sum)
			continue;
		j++;

		if (sony_fetchtrack((uint8_t*)buffer, buflen, &pos) != 0xDE)
			continue;
		j++;

		if (sony_fetchtrack((uint8_t*)buffer, buflen, &pos) != 0xAA)
			continue;
		j++;

		while((val = sony_fetchtrack((uint8_t*)buffer, buflen, &pos)) == 0xFF)
			j++;
		if (val != 0xD5)
			continue;   /* lost bit slip mark! */
		j++;

		if (sony_fetchtrack((uint8_t*)buffer, buflen, &pos) != 0xAA)
			continue;
		j++;

		if (sony_fetchtrack((uint8_t*)buffer, buflen, &pos) != 0xAD)
			continue;
		j++;

		/* should this be regarded as a critical error ??? */
		if (rev_diskbytes[sony_fetchtrack((uint8_t*)buffer, buflen, &pos)] != sector)
			continue;
		j++;

		for (i = 0; i < ARRAY_LENGTH(nibble_data); i++)
		{
			nibble_data[i] = rev_diskbytes[sony_fetchtrack((uint8_t*)buffer, buflen, &pos)];
			j++;
		}

		for (i = 3; i >= 0; i--)
		{
			/* should be checking checksum */
			sony_fetchtrack((uint8_t*)buffer, buflen, &pos);
		}

		sony_fetchtrack((uint8_t*)buffer, buflen, &pos);  /* should get 0xDE */
		sony_fetchtrack((uint8_t*)buffer, buflen, &pos);  /* should get 0xAA */
		sony_fetchtrack((uint8_t*)buffer, buflen, &pos);  /* should get 0xFF */

		/* did we already write this sector? */
		if ((found_sectors & (1 << sector)) == 0)
		{
			sony_denibblize35(sector_data, nibble_data, checksum);

			/* write the sector */
			err = apple35_write_sector_td(floppy, head, track, sector, sector_data, ARRAY_LENGTH(sector_data), 0);
			if (err)
				return err;

			found_sectors |= 1 << sector;
		}
	}
	return FLOPPY_ERROR_SUCCESS;
}



static floperr_t apple35_construct(floppy_image_legacy *floppy, uint32_t data_offset, uint32_t data_size,
	uint32_t tag_offset, uint32_t tag_size, int16_t format_byte, uint8_t sides, bool is_1440k)
{
	struct apple35_tag *tag;
	struct FloppyCallbacks *format;

	/* figure out format byte if not specified */
	if (format_byte < 0)
	{
		switch(sides)
		{
			case 1:
				format_byte = 0x02;
				break;
			case 2:
				format_byte = 0x22;
				break;
			default:
				return FLOPPY_ERROR_INVALIDIMAGE;
		}
	}

	/* create tag */
	tag = (struct apple35_tag *) floppy_create_tag(floppy, sizeof(struct apple35_tag));
	if (!tag)
		return FLOPPY_ERROR_OUTOFMEMORY;
	tag->data_offset = data_offset;
	tag->data_size = data_size;
	tag->tag_offset = tag_offset;
	tag->tag_size = tag_size;
	tag->format_byte = (uint8_t) format_byte;
	tag->sides = sides;
	tag->is_1440k = is_1440k ? 1 : 0;

	/* set up format callbacks */
	format = floppy_callbacks(floppy);
	format->read_sector = apple35_read_sector;
	format->write_sector = apple35_write_sector;
	format->read_track = apple35_read_track;
	format->write_track = apple35_write_track;
	format->get_sector_length = apple35_get_sector_length;
	format->get_heads_per_disk = apple35_get_heads_per_disk;
	format->get_tracks_per_disk = apple35_get_tracks_per_disk;
	format->get_track_size = apple35_get_track_size;
	return FLOPPY_ERROR_SUCCESS;
}



/* ----------------------------------------------------------------------- */

static FLOPPY_IDENTIFY(apple35_raw_identify)
{
	uint64_t size;
	size = floppy_image_size(floppy);
	*vote = ((size == 80*1*10*512) || (size == 80*2*10*512) || (size == (80*2*18*512)+84)
		|| (size == 80*2*18*512)) ? 100 : 0;
	return FLOPPY_ERROR_SUCCESS;
}




static FLOPPY_CONSTRUCT(apple35_raw_construct)
{
	uint64_t size;
	uint8_t sides;
	bool is_1440k;

	if (params)
	{
		/* create */
		sides = params->lookup_int(PARAM_HEADS);
		size = 80*sides*10*512;
		is_1440k = false;
	}
	else
	{
		/* load */
		size = floppy_image_size(floppy);
		if (size == 80*1*10*512)
		{
			sides = 1;
			is_1440k = false;
		}
		else if ((size == 80*2*10*512) || (size == 80*2*18*512) || (size == (80*2*18*512)+84))
		{
			sides = 2;
			is_1440k = (size == 80*2*18*512) || (size == (80*2*18*512)+84);
		}
		else
			return FLOPPY_ERROR_INVALIDIMAGE;
	}

	return apple35_construct(floppy, 0, (uint32_t) size, 0, 0, -1, sides, is_1440k);
}



/* ----------------------------------------------------------------------- */

struct header_diskcopy
{
	uint8_t disk_name[64];    /* name of the disk */
	uint32_t data_size;       /* total size of data for all sectors (512*number_of_sectors) */
	uint32_t tag_size;        /* total size of tag data for all sectors (12*number_of_sectors for GCR 3.5" floppies, 20*number_of_sectors for HD20, 0 otherwise) */
	uint32_t data_checksum;   /* CRC32 checksum of all sector data */
	uint32_t tag_checksum;    /* CRC32 checksum of all tag data */
	uint8_t disk_format;      /* 0 = 400K, 1 = 800K, 2 = 720K, 3 = 1440K  (other values reserved) */
	uint8_t format_byte;      /* should be $00 Apple II, $01 Lisa, $02 Mac MFS ??? */
							/* $12 = 400K, $22 = >400K Macintosh (DiskCopy uses this value for
							   all Apple II disks not 800K in size, and even for some of those),
							   $24 = 800K Apple II disk */
	uint16_t magic;           /* always $0100 (otherwise, the file may be in a different format. */
};



static floperr_t apple35_diskcopy_headerdecode(floppy_image_legacy *floppy, uint32_t *data_offset,
	uint32_t *data_size, uint32_t *tag_offset, uint32_t *tag_size, uint8_t *format_byte, uint8_t *sides)
{
	uint64_t size;
	struct header_diskcopy header;

	if (data_offset)
		*data_offset = 0;
	if (data_size)
		*data_size = 0;
	if (tag_offset)
		*tag_offset = 0;
	if (tag_size)
		*tag_size = 0;
	if (format_byte)
		*format_byte = 0;
	if (sides)
		*sides = 0;

	size = floppy_image_size(floppy);
	if (size < sizeof(struct header_diskcopy))
		return FLOPPY_ERROR_INVALIDIMAGE;

	floppy_image_read(floppy, &header, 0, sizeof(header));

	header.data_size = big_endianize_int32(header.data_size);
	header.tag_size = big_endianize_int32(header.tag_size);
	header.data_checksum = big_endianize_int32(header.data_checksum);
	header.tag_checksum = big_endianize_int32(header.tag_checksum);
	header.magic = big_endianize_int16(header.magic);

	if (header.disk_name[0] >= sizeof(header.disk_name))
		return FLOPPY_ERROR_INVALIDIMAGE;
	if (header.magic != 0x0100)
		return FLOPPY_ERROR_INVALIDIMAGE;
	if (size != (header.data_size + header.tag_size + sizeof(header)))
		return FLOPPY_ERROR_INVALIDIMAGE;

	if (header.data_size == 80*1*10*512)
	{
		if (sides)
			*sides = 1;
	}
	else if (header.data_size == 80*2*10*512)
	{
		if (sides)
			*sides = 2;
	}
	else
		return FLOPPY_ERROR_INVALIDIMAGE;

	if (data_offset)
		*data_offset = sizeof(header);
	if (data_size)
		*data_size = header.data_size;
	if (tag_offset)
		*tag_offset = sizeof(header) + header.data_size;
	if (tag_size)
		*tag_size = header.tag_size;
	if (format_byte)
		*format_byte = header.format_byte;
	return FLOPPY_ERROR_SUCCESS;
}



static FLOPPY_IDENTIFY(apple35_diskcopy_identify)
{
	*vote = apple35_diskcopy_headerdecode(floppy, nullptr, nullptr, nullptr, nullptr, nullptr, nullptr) ? 0 : 100;
	return FLOPPY_ERROR_SUCCESS;
}




static FLOPPY_CONSTRUCT(apple35_diskcopy_construct)
{
	floperr_t err;
	uint8_t format_byte, sides;
	uint32_t data_offset, data_size;
	uint32_t tag_offset, tag_size;
	int16_t format_byte_param = -1;
	struct header_diskcopy header;

	if (params)
	{
		/* create */
		sides = params->lookup_int(PARAM_HEADS);

		data_size = 80*sides*10*512;
		tag_size = 80*sides*10*12;

		memset(&header, 0, sizeof(header));
		header.data_size = big_endianize_int32(data_size);
		header.tag_size = big_endianize_int32(tag_size);
		header.disk_format = (sides > 1) ? 1 : 0;
		header.magic = big_endianize_int16(0x100);

		floppy_image_write(floppy, &header, 0, sizeof(header));
		floppy_image_write_filler(floppy, 0, sizeof(header), data_size + tag_size);
	}

	/* load */
	err = apple35_diskcopy_headerdecode(floppy, &data_offset, &data_size,
		&tag_offset, &tag_size, &format_byte, &sides);
	if (err)
		return err;

	format_byte_param = format_byte;

	return apple35_construct(floppy, data_offset, data_size,
		tag_offset, tag_size, format_byte_param, sides, false);
}



/* ----------------------------------------------------------------------- */

struct header_2img
{
	char magic[4];          /* '2IMG' */
	char creator[4];        /* signature; 'MESS' for MESS */
	uint16_t header_length;
	uint16_t version;
	uint32_t image_format;
	uint32_t flags;
	uint32_t block_count;
	uint32_t data_offset;
	uint32_t data_length;
	uint32_t comment_offset;
	uint32_t comment_length;
	uint32_t creator_offset;
	uint32_t creator_length;
	uint32_t padding[4];
};

#define IMAGE_FORMAT_DO     0
#define IMAGE_FORMAT_PO     1
#define IMAGE_FORMAT_NIB    2
#define IMAGE_FLAGS_LOCKED  0x80000000



static floperr_t apple35_2img_decode(floppy_image_legacy *floppy, uint32_t *image_format,
	uint32_t *data_offset, uint32_t *data_length)
{
	struct header_2img header;
	uint64_t size;

	if (image_format)
		*image_format = 0;
	if (data_offset)
		*data_offset = 0;
	if (data_length)
		*data_length = 0;

	size = floppy_image_size(floppy);
	if (size < sizeof(header))
	{
		return FLOPPY_ERROR_INVALIDIMAGE;
	}

	floppy_image_read(floppy, &header, 0, sizeof(header));

	if (memcmp(header.magic, "2IMG", 4))
	{
		return FLOPPY_ERROR_INVALIDIMAGE;
	}

	header.header_length    = little_endianize_int16(header.header_length);
	header.version          = little_endianize_int16(header.version);
	header.image_format     = little_endianize_int32(header.image_format);
	header.flags            = little_endianize_int32(header.flags);
	header.block_count      = little_endianize_int32(header.block_count);
	header.data_offset      = little_endianize_int32(header.data_offset);
	header.data_length      = little_endianize_int32(header.data_length);
	header.comment_offset   = little_endianize_int32(header.comment_offset);
	header.comment_length   = little_endianize_int32(header.comment_length);
	header.creator_offset   = little_endianize_int32(header.creator_offset);
	header.creator_length   = little_endianize_int32(header.creator_length);

	// at least some images "in the wild" (e.g. TOSEC Minor Set 1) have big-endian data sizes
	// even though that's against the .2mg spec
	if (header.data_length == 0x800c00)
	{
		LOG_FORMATS("ap_dsk35: corrected bad-endian data length\n");
		header.data_length = 0x0c8000;
	}

	if ((((uint64_t) header.data_offset) + header.data_length) > size)
		return FLOPPY_ERROR_INVALIDIMAGE;
	if ((((uint64_t) header.comment_offset) + header.comment_length) > size)
		return FLOPPY_ERROR_INVALIDIMAGE;
	if ((((uint64_t) header.creator_offset) + header.creator_length) > size)
		return FLOPPY_ERROR_INVALIDIMAGE;
	if ((header.image_format != IMAGE_FORMAT_DO) &&
			(header.image_format != IMAGE_FORMAT_PO) &&
			(header.image_format != IMAGE_FORMAT_NIB))
		return FLOPPY_ERROR_INVALIDIMAGE;

	if (image_format)
		*image_format = header.image_format;
	if (data_offset)
		*data_offset = header.data_offset;
	if (data_length)
		*data_length = header.data_length;
	return FLOPPY_ERROR_SUCCESS;
}



static FLOPPY_IDENTIFY(apple35_2img_identify)
{
	*vote = apple35_2img_decode(floppy, nullptr, nullptr, nullptr) ? 0 : 100;
	return FLOPPY_ERROR_SUCCESS;
}



static FLOPPY_CONSTRUCT(apple35_2img_construct)
{
	floperr_t err;
	uint32_t image_format;
	uint32_t data_offset;
	uint32_t data_size;
	uint8_t sides = 2;
	struct header_2img header;

	if (params)
	{
		/* create */
		sides = params->lookup_int(PARAM_HEADS);

		data_offset = sizeof(header);
		data_size = 80*sides*10*512;

		memset(&header, 0, sizeof(header));
		header.header_length    = little_endianize_int16(sizeof(header));
		header.block_count      = little_endianize_int32(80*sides*10);
		header.data_offset      = little_endianize_int32(data_offset);
		header.data_length      = little_endianize_int32(data_size);

		floppy_image_write(floppy, &header, 0, sizeof(header));
		floppy_image_write_filler(floppy, 0, sizeof(header), data_size);
	}
	else
	{
		/* load */
		err = apple35_2img_decode(floppy, &image_format, &data_offset, &data_size);
		if (err)
			return err;

		if (data_size == 80*1*10*512)
			sides = 1;  /* single sided */
		else if (data_size == 80*2*10*512)
			sides = 2;  /* double sided */
		else
			sides = 2;  /* unknown... what to do... */
	}

	return apple35_construct(floppy, data_offset, data_size,
		0, 0, -1, sides, false);
}



LEGACY_FLOPPY_OPTIONS_START( apple35_mac )
	LEGACY_FLOPPY_OPTION( apple35_raw, "dsk,img,image", "Apple raw 3.5\" disk image",   apple35_raw_identify,       apple35_raw_construct, nullptr,
		HEADS([1]-2)
		TRACKS([80])
		SECTOR_LENGTH([512])
		FIRST_SECTOR_ID([0]))
	LEGACY_FLOPPY_OPTION( apple35_dc, "dc,dc42,dsk,img,image",  "Apple DiskCopy disk image",    apple35_diskcopy_identify,  apple35_diskcopy_construct, nullptr,
		HEADS([1]-2)
		TRACKS([80])
		SECTOR_LENGTH([512])
		FIRST_SECTOR_ID([0]))
LEGACY_FLOPPY_OPTIONS_END

LEGACY_FLOPPY_OPTIONS_START( apple35_iigs )
	LEGACY_FLOPPY_OPTION( apple35_raw, "dsk,img,image,po", "Apple raw 3.5\" disk image",   apple35_raw_identify,       apple35_raw_construct, nullptr,
		HEADS([1]-2)
		TRACKS([80])
		SECTOR_LENGTH([512])
		FIRST_SECTOR_ID([0]))
	LEGACY_FLOPPY_OPTION( apple35_dc, "dc,dsk,img,image",   "Apple DiskCopy disk image",    apple35_diskcopy_identify,  apple35_diskcopy_construct, nullptr,
		HEADS([1]-2)
		TRACKS([80])
		SECTOR_LENGTH([512])
		FIRST_SECTOR_ID([0]))
	LEGACY_FLOPPY_OPTION( apple35_2img, "2img,2mg",     "Apple ][gs 2IMG disk image",   apple35_2img_identify,      apple35_2img_construct, nullptr,
		HEADS([1]-2)
		TRACKS([80])
		SECTOR_LENGTH([512])
		FIRST_SECTOR_ID([0]))
LEGACY_FLOPPY_OPTIONS_END


// license:BSD-3-Clause
// copyright-holders:Olivier Galibert
dc42_format::dc42_format() : floppy_image_format_t()
{
}

const char *dc42_format::name() const
{
	return "dc42";
}

const char *dc42_format::description() const
{
	return "DiskCopy 4.2 image";
}

const char *dc42_format::extensions() const
{
	return "dc42";
}

bool dc42_format::supports_save() const
{
	return true;
}

int dc42_format::identify(io_generic *io, uint32_t form_factor)
{
	uint8_t h[0x54];
	uint64_t size = io_generic_size(io);
	if(size < 0x54)
		return 0;

	io_generic_read(io, h, 0, 0x54);
	uint32_t dsize = (h[0x40] << 24) | (h[0x41] << 16) | (h[0x42] << 8) | h[0x43];
	uint32_t tsize = (h[0x44] << 24) | (h[0x45] << 16) | (h[0x46] << 8) | h[0x47];

	return size == 0x54+tsize+dsize && h[0] < 64 && h[0x52] == 1 && h[0x53] == 0 ? 100 : 0;
}

const floppy_image_format_t::desc_e dc42_format::mac_gcr[] = {
	{ SECTOR_LOOP_START, 0, -1 },
	{   RAWBITS, 0xff3fcf, 24 }, { RAWBITS, 0xf3fcff, 24 },
	{   RAWBITS, 0xff3fcf, 24 }, { RAWBITS, 0xf3fcff, 24 },
	{   RAWBITS, 0xff3fcf, 24 }, { RAWBITS, 0xf3fcff, 24 },
	{   RAWBITS, 0xff3fcf, 24 }, { RAWBITS, 0xf3fcff, 24 },
	{   RAWBITS, 0xff3fcf, 24 }, { RAWBITS, 0xf3fcff, 24 },
	{   RAWBITS, 0xff3fcf, 24 }, { RAWBITS, 0xf3fcff, 24 },
	{   RAWBITS, 0xff3fcf, 24 }, { RAWBITS, 0xf3fcff, 24 },
	{   RAWBITS, 0xff3fcf, 24 }, { RAWBITS, 0xf3fcff, 24 },
	{   RAWBITS, 0xd5aa96, 24 },
	{   CRC_MACHEAD_START, 0 },
	{     TRACK_ID_GCR6 },
	{     SECTOR_ID_GCR6 },
	{     TRACK_HEAD_ID_GCR6 },
	{     SECTOR_INFO_GCR6 },
	{   CRC_END, 0 },
	{   CRC, 0 },
	{   RAWBITS, 0xdeaaff, 24 },
	{   RAWBITS, 0xff3fcf, 24 }, { RAWBITS, 0xf3fcff, 24 },
	{   RAWBITS, 0xd5aaad, 24 },
	{   SECTOR_ID_GCR6 },
	{   SECTOR_DATA_MAC, -1 },
	{   RAWBITS, 0xdeaaff, 24 },
	{   RAWBITS, 0xff, 8 },
	{ SECTOR_LOOP_END },
	{ END },
};


bool dc42_format::load(io_generic *io, uint32_t form_factor, floppy_image *image)
{
	uint8_t h[0x54];
	io_generic_read(io, h, 0, 0x54);
	int dsize = (h[0x40] << 24) | (h[0x41] << 16) | (h[0x42] << 8) | h[0x43];
	int tsize = (h[0x44] << 24) | (h[0x45] << 16) | (h[0x46] << 8) | h[0x47];

	uint8_t encoding = h[0x50];
	uint8_t format = h[0x51];

	if((encoding != 0x00 || format != 0x02) && (encoding != 0x01 || format != 0x22)) {
		osd_printf_error("dc42: Unsupported encoding/format combination %02x/%02x\n", encoding, format);
		return false;
	}

	uint8_t sector_data[(512+12)*12];
	memset(sector_data, 0, sizeof(sector_data));

	desc_s sectors[12];

	int pos_data = 0x54;
	int pos_tag = 0x54+dsize;

	int head_count = encoding == 1 ? 2 : 1;

	for(int track=0; track < 80; track++) {
		for(int head=0; head < head_count; head++) {
			int ns = 12 - (track/16);
			int si = 0;
			for(int i=0; i<ns; i++) {
				uint8_t *data = sector_data + (512+12)*i;
				sectors[si].data = data;
				sectors[si].size = 512+12;
				sectors[si].sector_id = i;
				sectors[si].sector_info = format;
				if(tsize) {
					io_generic_read(io, data, pos_tag, 12);
					pos_tag += 12;
				}
				io_generic_read(io, data+12, pos_data, 512);
				pos_data += 512;
				si = (si + 2) % ns;
				if(si == 0)
					si++;
			}
			generate_track(mac_gcr, track, head, sectors, ns, 6208*ns, image);
		}
	}
	return true;
}

uint8_t dc42_format::gb(const uint8_t *buf, int ts, int &pos, int &wrap)
{
	uint8_t v = 0;
	int w1 = wrap;
	while(wrap != w1+2 && !(v & 0x80)) {
		v = v << 1 | ((buf[pos >> 3] >> (7-(pos & 7))) & 1);
		pos++;
		if(pos == ts) {
			pos = 0;
			wrap++;
		}
	}
	return v;
}

void dc42_format::update_chk(const uint8_t *data, int size, uint32_t &chk)
{
	for(int i=0; i<size; i+=2) {
		chk += (data[i] << 8) | data[i+1];
		chk = (chk >> 1) | (chk << 31);
	}
}

bool dc42_format::save(io_generic *io, floppy_image *image)
{
	int g_tracks, g_heads;
	image->get_actual_geometry(g_tracks, g_heads);

	if(g_heads == 0)
		g_heads = 1;

	uint8_t h[0x54];
	memset(h, 0, 0x54);
	strcpy((char *)h+1, "Unnamed");
	h[0] = 7;
	int nsect = 16*(12+11+10+9+8)*g_heads;
	uint32_t dsize = nsect*512;
	uint32_t tsize = nsect*12;
	h[0x40] = dsize >> 24;
	h[0x41] = dsize >> 16;
	h[0x42] = dsize >> 8;
	h[0x43] = dsize;
	h[0x44] = tsize >> 24;
	h[0x45] = tsize >> 16;
	h[0x46] = tsize >> 8;
	h[0x47] = tsize;
	h[0x50] = g_heads == 2 ? 0x01 : 0x00;
	h[0x51] = g_heads == 2 ? 0x22 : 0x02;
	h[0x52] = 0x01;
	h[0x53] = 0x00;

	uint32_t dchk = 0;
	uint32_t tchk = 0;

	int pos_data = 0x54;
	int pos_tag = 0x54+dsize;

	for(int track=0; track < 80; track++) {
		for(int head=0; head < g_heads; head++) {
			uint8_t sectdata[(512+12)*12];
			memset(sectdata, 0, sizeof(sectdata));
			int nsect = 12-(track/16);
			uint8_t buf[13000];
			int ts;
			generate_bitstream_from_track(track, head, 200000000/(6208*nsect), buf, ts, image);
			int pos = 0;
			int wrap = 0;
			int hb = 0;
			for(;;) {
				uint8_t v = gb(buf, ts, pos, wrap);
				if(v == 0xff)
					hb = 1;
				else if(hb == 1 && v == 0xd5)
					hb = 2;
				else if(hb == 2 && v == 0xaa)
					hb = 3;
				else if(hb == 3 && v == 0x96)
					hb = 4;
				else
					hb = 0;

				if(hb == 4) {
					uint8_t h[7];
					for(auto & elem : h)
						elem = gb(buf, ts, pos, wrap);
					uint8_t v2 = gcr6bw_tb[h[2]];
					uint8_t v3 = gcr6bw_tb[h[3]];
					uint8_t tr = gcr6bw_tb[h[0]] | (v2 & 1 ? 0x40 : 0x00);
					uint8_t se = gcr6bw_tb[h[1]];
					uint8_t si = v2 & 0x20 ? 1 : 0;
					//                  uint8_t ds = v3 & 0x20 ? 1 : 0;
					//                  uint8_t fmt = v3 & 0x1f;
					uint8_t c1 = (tr^se^v2^v3) & 0x3f;
					uint8_t chk = gcr6bw_tb[h[4]];
					if(chk == c1 && tr == track && si == head && se < nsect) {
						int opos = pos;
						int owrap = wrap;
						hb = 0;
						for(int i=0; i<20 && hb != 4; i++) {
							v = gb(buf, ts, pos, wrap);
							if(v == 0xff)
								hb = 1;
							else if(hb == 1 && v == 0xd5)
								hb = 2;
							else if(hb == 2 && v == 0xaa)
								hb = 3;
							else if(hb == 3 && v == 0xad)
								hb = 4;
							else
								hb = 0;
						}
						if(hb == 4) {
							uint8_t *dest = sectdata+(512+12)*se;
							gb(buf, ts, pos, wrap); // Ignore the sector byte
							uint8_t ca = 0, cb = 0, cc = 0;
							for(int i=0; i<522/3+1; i++) {
								uint8_t e0 = gb(buf, ts, pos, wrap);
								uint8_t e1 = gb(buf, ts, pos, wrap);
								uint8_t e2 = gb(buf, ts, pos, wrap);
								uint8_t e3 = i == 522/3 ? 0x96 : gb(buf, ts, pos, wrap);
								uint8_t va, vb, vc;
								gcr6_decode(e0, e1, e2, e3, va, vb, vc);
								cc = (cc << 1) | (cc >> 7);
								va = va ^ cc;
								int suma = ca + va + (cc & 1);
								ca = suma;
								vb = vb ^ ca;
								int sumb = cb + vb + (suma >> 8);
								cb = sumb;
								vc = vc ^ cb;
								cc = cc + vc + (sumb >> 8);
								*dest++ = va;
								*dest++ = vb;
								if(i != 522/3)
									*dest++ = vc;
							}
						} else {
							pos = opos;
							wrap = owrap;
						}
					}
					hb = 0;
				}
				if(wrap)
					break;
			}
			for(int i=0; i<nsect; i++) {
				uint8_t *data = sectdata + (512+12)*i;
				io_generic_write(io, data, pos_tag, 12);
				io_generic_write(io, data+12, pos_data, 512);
				pos_tag += 12;
				pos_data += 512;
				if(track || head || i)
					update_chk(data, 12, tchk);
				update_chk(data+12, 512, dchk);
			}
		}
	}

	h[0x48] = dchk >> 24;
	h[0x49] = dchk >> 16;
	h[0x4a] = dchk >> 8;
	h[0x4b] = dchk;
	h[0x4c] = tchk >> 24;
	h[0x4d] = tchk >> 16;
	h[0x4e] = tchk >> 8;
	h[0x4f] = tchk;

	io_generic_write(io, h, 0, 0x54);
	return true;
}

const floppy_format_type FLOPPY_DC42_FORMAT = &floppy_image_format_creator<dc42_format>;
