/* 
 * checksum.c   -compute a CRC 32-bit checksum for a file
 * Distributed as part of sula, an IRC client for X.
 * 
 * This file was part of LyX,  the High Level Word Processor
 * The function checksum is taken  from GNU textutill-1.22 and is there part of
 * the program cksum(1).
 *
 * The  cksum program is written by Q. Frank Xia, qx@math.columbia.edu.
 *
 * Modified for use in LyX by Lars G. Bjønnes.
 * Modified for use in sula by Tano Fotang, Feb 1998:
 *		o increased # of parameters to 3
 *		o return value is no longer the checksum but error status
 *		o partial checksum
 *		o added type Checksum, changed type for crctab[]
 *		o added checksum.h
 *		o use pointer pbuf to buffer
 */

/* #include "config.h" */
#include <stdio.h>
#include <errno.h>
#include "checksum.h"

/* Number of bytes to read at once.  */
#define BUFLEN (1 << 16)

/* DO _NOT_ CHANGE _ANYTHING_ IN THIS TABLE */
static const CheckSum crctab[256] =
{
	0x0,
	0x04C11DB7, 0x09823B6E, 0x0D4326D9, 0x130476DC, 0x17C56B6B,
	0x1A864DB2, 0x1E475005, 0x2608EDB8, 0x22C9F00F, 0x2F8AD6D6,
	0x2B4BCB61, 0x350C9B64, 0x31CD86D3, 0x3C8EA00A, 0x384FBDBD,
	0x4C11DB70, 0x48D0C6C7, 0x4593E01E, 0x4152FDA9, 0x5F15ADAC,
	0x5BD4B01B, 0x569796C2, 0x52568B75, 0x6A1936C8, 0x6ED82B7F,
	0x639B0DA6, 0x675A1011, 0x791D4014, 0x7DDC5DA3, 0x709F7B7A,
	0x745E66CD, 0x9823B6E0, 0x9CE2AB57, 0x91A18D8E, 0x95609039,
	0x8B27C03C, 0x8FE6DD8B, 0x82A5FB52, 0x8664E6E5, 0xBE2B5B58,
	0xBAEA46EF, 0xB7A96036, 0xB3687D81, 0xAD2F2D84, 0xA9EE3033,
	0xA4AD16EA, 0xA06C0B5D, 0xD4326D90, 0xD0F37027, 0xDDB056FE,
	0xD9714B49, 0xC7361B4C, 0xC3F706FB, 0xCEB42022, 0xCA753D95,
	0xF23A8028, 0xF6FB9D9F, 0xFBB8BB46, 0xFF79A6F1, 0xE13EF6F4,
	0xE5FFEB43, 0xE8BCCD9A, 0xEC7DD02D, 0x34867077, 0x30476DC0,
	0x3D044B19, 0x39C556AE, 0x278206AB, 0x23431B1C, 0x2E003DC5,
	0x2AC12072, 0x128E9DCF, 0x164F8078, 0x1B0CA6A1, 0x1FCDBB16,
	0x018AEB13, 0x054BF6A4, 0x0808D07D, 0x0CC9CDCA, 0x7897AB07,
	0x7C56B6B0, 0x71159069, 0x75D48DDE, 0x6B93DDDB, 0x6F52C06C,
	0x6211E6B5, 0x66D0FB02, 0x5E9F46BF, 0x5A5E5B08, 0x571D7DD1,
	0x53DC6066, 0x4D9B3063, 0x495A2DD4, 0x44190B0D, 0x40D816BA,
	0xACA5C697, 0xA864DB20, 0xA527FDF9, 0xA1E6E04E, 0xBFA1B04B,
	0xBB60ADFC, 0xB6238B25, 0xB2E29692, 0x8AAD2B2F, 0x8E6C3698,
	0x832F1041, 0x87EE0DF6, 0x99A95DF3, 0x9D684044, 0x902B669D,
	0x94EA7B2A, 0xE0B41DE7, 0xE4750050, 0xE9362689, 0xEDF73B3E,
	0xF3B06B3B, 0xF771768C, 0xFA325055, 0xFEF34DE2, 0xC6BCF05F,
	0xC27DEDE8, 0xCF3ECB31, 0xCBFFD686, 0xD5B88683, 0xD1799B34,
	0xDC3ABDED, 0xD8FBA05A, 0x690CE0EE, 0x6DCDFD59, 0x608EDB80,
	0x644FC637, 0x7A089632, 0x7EC98B85, 0x738AAD5C, 0x774BB0EB,
	0x4F040D56, 0x4BC510E1, 0x46863638, 0x42472B8F, 0x5C007B8A,
	0x58C1663D, 0x558240E4, 0x51435D53, 0x251D3B9E, 0x21DC2629,
	0x2C9F00F0, 0x285E1D47, 0x36194D42, 0x32D850F5, 0x3F9B762C,
	0x3B5A6B9B, 0x0315D626, 0x07D4CB91, 0x0A97ED48, 0x0E56F0FF,
	0x1011A0FA, 0x14D0BD4D, 0x19939B94, 0x1D528623, 0xF12F560E,
	0xF5EE4BB9, 0xF8AD6D60, 0xFC6C70D7, 0xE22B20D2, 0xE6EA3D65,
	0xEBA91BBC, 0xEF68060B, 0xD727BBB6, 0xD3E6A601, 0xDEA580D8,
	0xDA649D6F, 0xC423CD6A, 0xC0E2D0DD, 0xCDA1F604, 0xC960EBB3,
	0xBD3E8D7E, 0xB9FF90C9, 0xB4BCB610, 0xB07DABA7, 0xAE3AFBA2,
	0xAAFBE615, 0xA7B8C0CC, 0xA379DD7B, 0x9B3660C6, 0x9FF77D71,
	0x92B45BA8, 0x9675461F, 0x8832161A, 0x8CF30BAD, 0x81B02D74,
	0x857130C3, 0x5D8A9099, 0x594B8D2E, 0x5408ABF7, 0x50C9B640,
	0x4E8EE645, 0x4A4FFBF2, 0x470CDD2B, 0x43CDC09C, 0x7B827D21,
	0x7F436096, 0x7200464F, 0x76C15BF8, 0x68860BFD, 0x6C47164A,
	0x61043093, 0x65C52D24, 0x119B4BE9, 0x155A565E, 0x18197087,
	0x1CD86D30, 0x029F3D35, 0x065E2082, 0x0B1D065B, 0x0FDC1BEC,
	0x3793A651, 0x3352BBE6, 0x3E119D3F, 0x3AD08088, 0x2497D08D,
	0x2056CD3A, 0x2D15EBE3, 0x29D4F654, 0xC5A92679, 0xC1683BCE,
	0xCC2B1D17, 0xC8EA00A0, 0xD6AD50A5, 0xD26C4D12, 0xDF2F6BCB,
	0xDBEE767C, 0xE3A1CBC1, 0xE760D676, 0xEA23F0AF, 0xEEE2ED18,
	0xF0A5BD1D, 0xF464A0AA, 0xF9278673, 0xFDE69BC4, 0x89B8FD09,
	0x8D79E0BE, 0x803AC667, 0x84FBDBD0, 0x9ABC8BD5, 0x9E7D9662,
	0x933EB0BB, 0x97FFAD0C, 0xAFB010B1, 0xAB710D06, 0xA6322BDF,
	0xA2F33668, 0xBCB4666D, 0xB8757BDA, 0xB5365D03, 0xB1F740B4
};

/* Calculate the checksum of file FILE. Return 0 if successful, >0 (errno is
 * * set)  or <0 if an error occurs. fotang, 2/98*/
/* if offset>=0  then compute checksum only for the first _offset_ bytes of the file.
offset<0 is equivalent to checksum(f,filesize,&cks). 
----------fotang, 3/98 */
int     checksum(const char *fname, int offset, CheckSum * cks)

{
	{

		FILE   *fp = fopen(fname, "r");

		if (!fp)
			return errno;
		else {
			long    n;
			long    length = 0;
			unsigned char buf[BUFLEN], *pbuf;

			*cks = 0;
			while ((n = fread(buf, sizeof(unsigned char), BUFLEN, fp)) > 0) {
				pbuf = buf;
				length += n;
				if(offset>-1 && length>(offset)){
					n=n-length+offset;
					length=offset;
				}
				while (pbuf - buf < n)
					*cks = (*cks << 8) ^ crctab[((*cks >> 24) ^ *(pbuf++)) & 0xFF];
			}
			if (ferror(fp)) {
				fclose(fp);
				return -1;
			}
			
			/* --chagned to plain fclose(fp). 19/3/98, fotang 
			if (fclose(fp) == EOF)
				return errno;*/
			fclose(fp);
			while (length > 0) {
				*cks = (*cks << 8) ^ crctab[((*cks >> 24) ^ length) & 0xFF];
				length >>= 8;
			}
			*cks = ~(*cks) & 0xFFFFFFFF;
			return 0;
		}
	}
}

