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