Index: glibc-2.7/libio/fileops.c
===================================================================
--- glibc-2.7.orig/libio/fileops.c	2007-10-23 08:46:13.000000000 -0400
+++ glibc-2.7/libio/fileops.c	2007-10-23 08:50:51.000000000 -0400
@@ -522,10 +522,19 @@
     fp->_cur_column = INTUSE(_IO_adjust_column) (fp->_cur_column - 1, data,
 						 count) + 1;
   _IO_setg (fp, fp->_IO_buf_base, fp->_IO_buf_base, fp->_IO_buf_base);
-  fp->_IO_write_base = fp->_IO_write_ptr = fp->_IO_buf_base;
-  fp->_IO_write_end = (fp->_mode <= 0
+  if (__builtin_expect (count == to_do, 1))
+    {
+      fp->_IO_write_base = fp->_IO_write_ptr = fp->_IO_buf_base;
+      fp->_IO_write_end = (fp->_mode <= 0
 		       && (fp->_flags & (_IO_LINE_BUF+_IO_UNBUFFERED))
 		       ? fp->_IO_buf_base : fp->_IO_buf_end);
+    }
+  else if (count > 0 && fp->_IO_write_base == data)
+    {
+      memmove (data, data+count, 
+               fp->_IO_write_ptr - fp->_IO_write_base - count);
+      fp->_IO_write_ptr -= count;
+    }
   return count;
 }