#include <stdio.h>
#include <windows.h>


  /* Table of CRCs of all 8-bit messages. */
   unsigned long crc_table[256];
   
   /* Flag: has the table been computed? Initially false. */
   int crc_table_computed = 0;
   
   /* Make the table for a fast CRC. */
   void make_crc_table(void)
   {
     unsigned long c;
     int n, k;
   
     for (n = 0; n < 256; n++) {
       c = (unsigned long) n;
       for (k = 0; k < 8; k++) {
         if (c & 1)
           c = 0xedb88320L ^ (c >> 1);
         else
           c = c >> 1;
       }
       crc_table[n] = c;
     }
     crc_table_computed = 1;
   }
   
   /* Update a running CRC with the bytes buf[0..len-1]--the CRC
      should be initialized to all 1's, and the transmitted value
      is the 1's complement of the final running CRC (see the
      crc() routine below)). */
   
   unsigned long update_crc(unsigned long crc, unsigned char *buf,
                            int len)
   {
     unsigned long c = crc;
     int n;
   
     if (!crc_table_computed)
       make_crc_table();
     for (n = 0; n < len; n++) {
       c = crc_table[(c ^ buf[n]) & 0xff] ^ (c >> 8);
     }
     return c;
   }
   
   /* Return the CRC of the bytes buf[0..len-1]. */
 void crc(unsigned char *buf, int len)
   {
		DWORD crcdata = update_crc(0xffffffffL, buf, len) ^ 0xffffffffL;
		for(int i = 0; i < 4; i ++)
		 {
			buf[len +3 -i] = crcdata & 0xff;
			crcdata >>= 8;
		 }
   }


void main(void)
 {
	BITMAPFILEHEADER fHead;
	BITMAPINFOHEADER iHead;
	BYTE *bits;

	FILE *Fin = fopen("input.bmp", "rb");
	fread(&fHead, sizeof(fHead), 1, Fin);
	fread(&iHead, sizeof(iHead), 1, Fin);
	bits = new BYTE[iHead.biWidth * iHead.biHeight *3];
	fread(bits, iHead.biWidth * iHead.biHeight *3, 1, Fin);
	fclose(Fin);

	BYTE buffer[65536];
	char *ptr = (char*)buffer;

	// -----------------------------------------------------------
	// シグネチャ作成
	sprintf(ptr, "%cPNG%c%c%c%c", 0x89, 0x0d, 0x0a, 0x1a, 0x0a);
	ptr += 8;

	// -----------------------------------------------------------
	// ヘッダ作成
	sprintf(ptr, "%c%c%c%c", 0,0,0,13);
	ptr += 4;

	int width = iHead.biWidth;
	int height = iHead.biHeight;
	sprintf(ptr, "IHDR"
					"%c%c%c%c"			// width
					"%c%c%c%c"			// height
					"%c%c%c%c%c",
							0,0,width >> 8,width & 0xff, //200,
							0,0,height >> 8, height & 0xff, //5,
							8,2,0,0,0);
	// CRC付加
	crc((BYTE*)ptr, 13+4);
	ptr += 13 +4 +4;

	// -----------------------------------------------------------
	// 画像データ準備
	// サイズ
	DWORD size = 1 +2 + 4 + height * (width*3 +1) + 4;	// 無圧縮指定 1
											// MODE       2
											// LEN + NLEN 4
											// bit data   width*4
											// Adler32    4

	sprintf(ptr, "%c%c%c%c", 0, (size >> 16) & 0xff, (size >> 8) & 0xff, size & 0xff);
	ptr += 4;

	char *basePtr = ptr;
	sprintf(ptr, "IDAT");
	ptr += 4;

	// 圧縮コードは常に同じ
	*ptr ++ = 0x78;
	// モード＋チェックも同じ
	DWORD md = 0x78c0 % 31;
	if(md)
		md = 0x78c0 + (31-md);
	else
		md = 0x78c0;
	*ptr ++ = md & 0xff;				// わかりにくいよ！

	*ptr ++ = 0x01;						// 無圧縮指定

	DWORD len = height * (width*3+1);

	if(len & 0xffff0000)
	 {
		puts("画像が大きすぎます");
		return;
	 }

	*ptr ++ = len & 0xff;
	*ptr ++ = len >> 8;						// LEN + NLEN
	len = ~len;
	*ptr ++ = len & 0xff;
	*ptr ++ = len >> 8;

	DWORD s1, s2;
	s1 = 1;
	s2 = 0;
	BYTE tempBuf[65536];
	int iPtr = 0;

	for(int y = 0; y < height; y ++)
	 {

		// 未圧縮データのチェックサムを計算(for zlib)

		tempBuf[iPtr ++] = 0x00;			// フィルタタイプ

		for(int x = 0; x < width; x ++)
		 {
			tempBuf[iPtr ++] = bits[(height -y -1)*width*3 + x*3 + 2];
			tempBuf[iPtr ++] = bits[(height -y -1)*width*3 + x*3 + 1];
			tempBuf[iPtr ++] = bits[(height -y -1)*width*3 + x*3 + 0];
		 }
	 }

	for(int i = 0; i < iPtr; i ++)
	 {
		s1 = (s1 + tempBuf[i]) % 65521;
		s2 = (s2 + s1) % 65521;
	 }

	tempBuf[iPtr ++] = (s2 >> 8) & 0xff;
	tempBuf[iPtr ++] = s2 & 0xff;
	tempBuf[iPtr ++] = (s1 >> 8) & 0xff;
	tempBuf[iPtr ++] = s1 & 0xff;

	// データをコピー
	memcpy(ptr, tempBuf, iPtr);

	ptr += iPtr;

	crc((BYTE*)basePtr, size +4);
	ptr += 4;

	// -----------------------------------------------------------
	// ターミネータ作成
	sprintf(ptr, "%c%c%c%c", 0,0,0,0);
	ptr += 4;
	sprintf(ptr, "IEND");
	// CRC付加
	crc((BYTE*)ptr, 4);
	ptr += 8;

	// -----------------------------------------------------------
	// 書き出し
	FILE *Fp = fopen("test.png", "wb");
	fwrite(buffer, ((DWORD)ptr) - ((DWORD)buffer), 1, Fp);
	fclose(Fp);
 }