// SPDX-License-Identifier: GPL-3.0-or-later

// Copyright (C) 2026 Alonso (GS·RUN). MSXFileForge.

// Free software under the GNU GPL v3 (or later) - see LICENSE. Modified

// versions must be distributed under the same license.

#include "util.h"

#include <cstring>

namespace msx {

uint32_t crc32(const uint8_t* data, size_t n) {

static uint32_t table[256];

static bool init = false;

if (!init) {

for (uint32_t i = 0; i < 256; ++i) {

uint32_t c = i;

for (int k = 0; k < 8; ++k) c = (c & 1) ? (0xEDB88320u ^ (c >> 1)) : (c >> 1);

table[i] = c;

}

init = true;

}

uint32_t crc = 0xFFFFFFFFu;

for (size_t i = 0; i < n; ++i) crc = table[(crc ^ data[i]) & 0xFF] ^ (crc >> 8);

return crc ^ 0xFFFFFFFFu;

}

static void wr16(uint8_t* p, uint16_t v) { p[0] = v & 0xFF; p[1] = v >> 8; }

std::vector<uint8_t> formatBlankImage(int totalSectors) {

// Standard MSX geometries.

int spc, ndir, spf, spt, heads; uint8_t media;

if (totalSectors == 720) { // 360KB SS

spc = 2; ndir = 112; spf = 2; spt = 9; heads = 1; media = 0xF8;

} else { // default 720KB DS

totalSectors = 1440;

spc = 2; ndir = 112; spf = 3; spt = 9; heads = 2; media = 0xF9;

}

std::vector<uint8_t> img((size_t)totalSectors * 512, 0);

uint8_t* b = img.data();

// Boot sector: JMP + OEM + BPB.

b[0] = 0xEB; b[1] = 0xFE; b[2] = 0x90;

memcpy(b + 3, "MSXFForg", 8);

wr16(b + 0x0B, 512); // bytes/sector

b[0x0D] = (uint8_t)spc; // sectors/cluster

wr16(b + 0x0E, 1); // reserved sectors

b[0x10] = 2; // number of FATs

wr16(b + 0x11, (uint16_t)ndir);

wr16(b + 0x13, (uint16_t)totalSectors);

b[0x15] = media;

wr16(b + 0x16, (uint16_t)spf);

wr16(b + 0x18, (uint16_t)spt);

wr16(b + 0x1A, (uint16_t)heads);

b[0x1FE] = 0x55; b[0x1FF] = 0xAA; // boot signature

// Initialize both FATs: reserved cluster 0/1 = media,FF,FF.

for (int f = 0; f < 2; ++f) {

long fatOff = (1 + (long)f * spf) * 512;

img[fatOff + 0] = media;

img[fatOff + 1] = 0xFF;

img[fatOff + 2] = 0xFF;

}

// Root directory + data area stay zeroed (empty).

return img;

}

} // namespace msx