#include <stdio.h>
#include <string.h>

#define     INCL_REXXSAA
#include    <rexxsaa.h>

#include "rxcrcdll.h"

/* This is the exported function, the one called from REXX */
ULONG RxGetCrc(CHAR *name,         /* Routine name */
               ULONG numargs,      /* Number of arguments */
               RXSTRING args[],    /* Null-terminated RXSTRINGs array*/
               CHAR *queuename,    /* Current external data queue name */
               RXSTRING *retstr)   /* returning RXSTRING  */
{
	char string[9];
	unsigned long crc;
	FILE   *fp;
	unsigned long crcTable[256];

	/* Check number of arguments */
	if (numargs!=1)
		return RETSTR_INVALID; 

	/* Generate the table */
	CrcGenTable(crcTable);

	/* The output string will be ERROR or the CRC value */
	if ((fp=fopen(args[0].strptr,"rb"))==NULL) 
	{
		strcpy(string,"ERROR");
	}
	else 
	{
		crc=CrcGetCrc(fp,crcTable);
		sprintf(string,"%08lx",crc);
	}

	fclose(fp);

	/* Copy the output string to the returned REXX string */
  	strcpy(retstr->strptr,string);
	retstr->strlength = strlen(string);
	
	/* Success !!! */
	return RETSTR_OK;
}

/* This function returns the CRC value of an opened file */
unsigned long CrcGetCrc(FILE *fp,unsigned long* crcTable)
{
	unsigned long crc = 0xFFFFFFFF;
	int c;

	while((c=getc(fp))!=EOF) 
		crc=((crc>>8)&0x00FFFFFF)^crcTable[(crc^c)&0xFF];

	crc^=0xFFFFFFFF;

	return crc;
}

/* This function generates a table of values used in CrcGetCrc */
void CrcGenTable(unsigned long* crcTable)
{
	unsigned long	crc, poly;
	int	i, j;

	poly = 0xEDB88320L;
	for (i=0;i<256;i++) 
	{
		crc=i;
		for (j=8;j>0;j--) 
			if (crc&1)
				crc=(crc>>1)^poly;
			else 
				crc>>=1;
		crcTable[i]=crc;
	}
}