[newlib-cygwin] newlib: fix fseek optimization with SEEK_CUR

[Corinna Vinschen <corinna@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=59362c80e3a02c011fd0ef3d7f07a20098d2a9d5

commit 59362c80e3a02c011fd0ef3d7f07a20098d2a9d5
Author: Bastien Bouclet <bastien.bouclet@gmail.com>
Date:   Sat Nov 9 17:28:04 2019 +0100

    newlib: fix fseek optimization with SEEK_CUR
    
    The call to fflush was invalidating the read buffer, preventing relative
    seeks to positions that would have been inside the read buffer from
    being optimized. The call to srefill would then re-read mostly the same
    data that was initially in the read buffer.

Diff:
---
 newlib/libc/stdio/fseeko.c     | 31 ++++++-------------------------
 newlib/libc/stdio64/fseeko64.c | 31 ++++++-------------------------
 2 files changed, 12 insertions(+), 50 deletions(-)

diff --git a/newlib/libc/stdio/fseeko.c b/newlib/libc/stdio/fseeko.c
index 3e0f9e9..bbf1af4 100644
--- a/newlib/libc/stdio/fseeko.c
+++ b/newlib/libc/stdio/fseeko.c
@@ -141,31 +141,12 @@ _fseeko_r (struct _reent *ptr,
   switch (whence)
     {
     case SEEK_CUR:
-      /*
-       * In order to seek relative to the current stream offset,
-       * we have to first find the current stream offset a la
-       * ftell (see ftell for details).
-       */
-      _fflush_r (ptr, fp);   /* may adjust seek offset on append stream */
-      if (fp->_flags & __SOFF)
-	curoff = fp->_offset;
-      else
-	{
-	  curoff = seekfn (ptr, fp->_cookie, (_fpos_t) 0, SEEK_CUR);
-	  if (curoff == -1L)
-	    {
-	      _newlib_flockfile_exit (fp);
-	      return EOF;
-	    }
-	}
-      if (fp->_flags & __SRD)
-	{
-	  curoff -= fp->_r;
-	  if (HASUB (fp))
-	    curoff -= fp->_ur;
-	}
-      else if (fp->_flags & __SWR && fp->_p != NULL)
-	curoff += fp->_p - fp->_bf._base;
+      curoff = _ftello_r(ptr, fp);
+      if (curoff == -1L)
+        {
+          _newlib_flockfile_exit (fp);
+          return EOF;
+        }
 
       offset += curoff;
       whence = SEEK_SET;
diff --git a/newlib/libc/stdio64/fseeko64.c b/newlib/libc/stdio64/fseeko64.c
index 0672086..f380055 100644
--- a/newlib/libc/stdio64/fseeko64.c
+++ b/newlib/libc/stdio64/fseeko64.c
@@ -142,31 +142,12 @@ _fseeko64_r (struct _reent *ptr,
   switch (whence)
     {
     case SEEK_CUR:
-      /*
-       * In order to seek relative to the current stream offset,
-       * we have to first find the current stream offset a la
-       * ftell (see ftell for details).
-       */
-      _fflush_r (ptr, fp);   /* may adjust seek offset on append stream */
-      if (fp->_flags & __SOFF)
-	curoff = fp->_offset;
-      else
-	{
-	  curoff = seekfn (ptr, fp->_cookie, (_fpos64_t) 0, SEEK_CUR);
-	  if (curoff == -1L)
-	    {
-	      _newlib_flockfile_exit(fp);
-	      return EOF;
-	    }
-	}
-      if (fp->_flags & __SRD)
-	{
-	  curoff -= fp->_r;
-	  if (HASUB (fp))
-	    curoff -= fp->_ur;
-	}
-      else if (fp->_flags & __SWR && fp->_p != NULL)
-	curoff += fp->_p - fp->_bf._base;
+      curoff = _ftello64_r(ptr, fp);
+      if (curoff == -1L)
+        {
+          _newlib_flockfile_exit (fp);
+          return EOF;
+        }
 
       offset += curoff;
       whence = SEEK_SET;