From: Nigel Stephens <nigel AT algor DOT co DOT uk>
Date: Wed, 24 Aug 94 16:19:50 +0100
To: djgpp AT sun DOT soe DOT clarkson DOT edu
Subject: Bug in fseek

I have discovered a bug in the fseek routine in the 1.12 C library.  A
recent change to it disabled the offset adjustment which accounted for
data that had already been read into the stdio buffer.  This totally
broke relative (i.e. SEEK_CUR) fseeks.

The following patch to libsrc/c/io/fseek.c reenables the offset/buffer
synchronisation, but removes the spurious code that tried to align the
seek to a word boundary, and would have broken backward relative
seeks.  I have rebuilt fseek with these changes and it now appears to
work correctly.

===================================================================
RCS file: fseek.c,v
retrieving revision 1.1
diff -c -r1.1 fseek.c
*** 1.1	1994/08/22 16:04:07
--- fseek.c	1994/08/22 16:01:09
***************
*** 24,49 ****
  	register FILE *iop;
  	long offset;
  {
! 	register resync, c;
  	long p = -1;			/* can't happen? */
  	long adjust = 0;
  	char *q, *qq;
  
  	iop->_flag &= ~_IOEOF;
  	if (iop->_flag&_IOREAD) {
! #if 0
! 		if (ptrname<2 && iop->_base &&
  			!(iop->_flag&_IONBF)) {
  			c = iop->_cnt;
  			p = offset;
! 			if (ptrname==0) {
  				long curpos = lseek(fileno(iop), 0L, 1);
  				if (curpos == -1)
  					return (-1);
  				p += c - curpos;
  			} else
  				offset -= c;
! 			if(!(iop->_flag&_IORW) && c>0&&p<=c
  			    && p>=iop->_base-iop->_ptr){
  				if (iop->_flag&_IOTEXT){
  				  q = &iop->_ptr[iop->_cnt];
--- 24,48 ----
  	register FILE *iop;
  	long offset;
  {
! 	register long c;
  	long p = -1;			/* can't happen? */
  	long adjust = 0;
  	char *q, *qq;
  
  	iop->_flag &= ~_IOEOF;
  	if (iop->_flag&_IOREAD) {
! 		if (ptrname!=SEEK_END && iop->_base &&
  			!(iop->_flag&_IONBF)) {
  			c = iop->_cnt;
  			p = offset;
! 			if (ptrname==SEEK_SET) {
  				long curpos = lseek(fileno(iop), 0L, 1);
  				if (curpos == -1)
  					return (-1);
  				p += c - curpos;
  			} else
  				offset -= c;
! 			if(!(iop->_flag&_IORW) && c>0 && p<=c
  			    && p>=iop->_base-iop->_ptr){
  				if (iop->_flag&_IOTEXT){
  				  q = &iop->_ptr[iop->_cnt];
***************
*** 58,79 ****
  				iop->_cnt -= (int)p;
  				return(0);
  			}
! 			resync = offset&01;
! 		} else
! 			resync = 0;
! #endif
  		if (iop->_flag & _IORW) {
  			iop->_ptr = iop->_base;
  			iop->_flag &= ~_IOREAD;
- 			resync = 0;
  		}
! 		p = lseek(fileno(iop), offset-resync, ptrname);
  		iop->_cnt = 0;
- #if 0
- 		if (resync && p != -1)
- 			if (getc(iop) == EOF)
- 				p = -1;
- #endif
  	}
  	else if (iop->_flag & (_IOWRT|_IORW)) {
  		p = fflush(iop);
--- 57,69 ----
  				iop->_cnt -= (int)p;
  				return(0);
  			}
! 		}
  		if (iop->_flag & _IORW) {
  			iop->_ptr = iop->_base;
  			iop->_flag &= ~_IOREAD;
  		}
! 		p = lseek(fileno(iop), offset, ptrname);
  		iop->_cnt = 0;
  	}
  	else if (iop->_flag & (_IOWRT|_IORW)) {
  		p = fflush(iop);