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CPM OPERATING SYSTEMS/CPM 68K/1.0X SOURCES/v102a/clib/lseek.c

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+/***************************************************************************
+ *									    
+ *			    L s e e k   F u n c t i o n			    
+ *			    ---------------------------			    
+ *	Copyright 1982 by Digital Research Inc.  All rights reserved.	    
+ *									    
+ *	The lseek function changes the present position of reading	    
+ *	to or writing from a file.					    
+ *	The tell function returns the present position in a file.	    
+ *									    
+ *	Calling sequence:						    
+ *									    
+ *		ret = lseek(fd,offset,sense);				    
+ *	or	ret = tell(fd);						    
+ *									    
+ *	Where:								    
+ *									    
+ *		fd	Is an open file descriptor			    
+ *		offset	Is the (long) file offset			    
+ *		sense	Is the meaning of offset			    
+ *			0 => From the beginning of the file		    
+ *			1 => From the present file position		    
+ *			2 => From the end of the file			    
+ *									    
+ *		ret	Is the resulting absolute file offset		    
+ *			-1 indicates failure				    
+ *									    
+ ****************************************************************************/
+
+#include "portab.h"
+#include "osif.h"
+#include "osiferr.h"
+#include "errno.h"
+
+LONG	lseek(fd,offs,sense)			/* CLEAR FUNCTION ***********/
+						/*			    */
+	WORD	fd;				/* Open file descriptor	    */
+	LONG	offs;				/* File offset		    */
+	WORD	sense;				/* Sense of offset	    */
+						/*			    */
+						/****************************/
+{
+						/****************************/
+REG	FD	*fp;				/* File pointer		    */
+EXTERN	FD	*_chkc();			/* fd to fp translation	MGL */
+EXTERN	LONG	_filesz();			/* computes CP/M file size  */
+						/*			    */
+	if((fp = _chkc(fd)) == NULLFD)		/* Convert to pointer	    */
+		RETERR(FAILURE,EBADF);		/*   Can't		    */
+	switch(sense)				/****************************/
+	{					/*			    */
+	case	0:				/* From beginning of file   */
+		fp->offset = offs;		/* Just set to offset	    */
+		break;				/* Then quit		    */
+						/****************************/
+	case	1:				/* From present position    */
+		fp->offset += offs;		/*			    */
+		break;				/*			    */
+						/****************************/
+	case	2:				/* From end of file	    */
+		fp->hiwater = _filesz(fd);	/* go find the end of file  */
+		fp->offset = fp->hiwater + offs;/* compute from end of file */
+		break;				/*			    */
+						/****************************/
+	default:				/* All others NFG	    */
+		RETERR(FAILURE,EINVAL);		/*			    */
+	}					/****************************/
+	fp->flags &= ~ATEOF;			/* any seek clears EOF	    */
+	if( fp->offset < 0 )			/* bad seek call?	    */
+		fp->offset = -1;		/* set to uniform value	    */
+	return(fp->offset);			/* Return resultant offset  */
+}						/****************************/
+
+						/****************************/
+LONG	tell(fd)				/* CLEAR FUNCTION ***********/
+	WORD fd;				/* this file here	    */
+{						/*			    */
+	return(lseek(fd,0L,1));			/* is that all?		    */
+}						/****************************/