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mingw-fseek.c
/**
 * This file has no copyright assigned and is placed in the Public Domain.
 * This file is part of the w64 mingw-runtime package.
 * No warranty is given; refer to the file DISCLAIMER.PD within this package.
 */
#include <windows.h>
#include <stdio.h>
#include <io.h>
#include <stdlib.h>

#define ZEROBLOCKSIZE 512
static int __mingw_fseek_called;

int __mingw_fseek (FILE *fp, int offset, int whence);

int
__mingw_fseek (FILE *fp, int offset, int whence)
{
# undef fseek 
  __mingw_fseek_called = 1;
  return fseek (fp, offset, whence);
}

int __mingw_fseeko64 (FILE *fp, long offset, int whence);

int
__mingw_fseeko64 (FILE *fp, long offset, int whence)
{
# undef fseeko64
  __mingw_fseek_called = 1;
  return fseeko64 (fp, offset, whence);
}

size_t __mingw_fwrite (const void *buffer, size_t size, size_t count, FILE *fp);

size_t
__mingw_fwrite (const void *buffer, size_t size, size_t count, FILE *fp)
{
# undef fwrite 
  if ((_osver & 0x8000) &&  __mingw_fseek_called)
    {
      ULARGE_INTEGER actual_length;
      LARGE_INTEGER current_position;

      memset (&current_position, 0, sizeof (LARGE_INTEGER));
      __mingw_fseek_called = 0;
      fflush (fp);
      actual_length.LowPart = GetFileSize ((HANDLE) _get_osfhandle (fileno (fp)), 
                                 &actual_length.HighPart);
      if (actual_length.LowPart == 0xFFFFFFFF 
          && GetLastError() != NO_ERROR )
        return -1;
      current_position.LowPart = SetFilePointer ((HANDLE) _get_osfhandle (fileno (fp)),
                                           current_position.LowPart,
                                     &current_position.HighPart,
                                     FILE_CURRENT);
      if (current_position.LowPart == 0xFFFFFFFF
          && GetLastError() != NO_ERROR )
        return -1;

#ifdef DEBUG
      printf ("__mingw_fwrite: current %I64u, actual %I64u\n", 
            current_position.QuadPart, actual_length.QuadPart);
#endif /* DEBUG */
      if ((size_t)current_position.QuadPart > (size_t)actual_length.QuadPart)
      {
        static char __mingw_zeros[ZEROBLOCKSIZE];
        long long numleft;

        SetFilePointer ((HANDLE) _get_osfhandle (fileno (fp)), 
                        0, 0, FILE_END);
        numleft = current_position.QuadPart - actual_length.QuadPart;

#ifdef DEBUG
        printf ("__mingw_fwrite: Seeking %I64d bytes past end\n", numleft);
#endif /* DEBUG */
        while (numleft > 0LL)
          {
            DWORD nzeros = (numleft > ZEROBLOCKSIZE)
                           ? ZEROBLOCKSIZE : numleft;
            DWORD written;
            if (! WriteFile ((HANDLE) _get_osfhandle (fileno (fp)),
                             __mingw_zeros, nzeros, &written, NULL))
              {
              /* Best we can hope for, or at least DJ says so. */
                SetFilePointer ((HANDLE) _get_osfhandle (fileno (fp)), 
                                0, 0, FILE_BEGIN);
              return -1;
            }
            if (written < nzeros)
              {
              /* Likewise. */
                SetFilePointer ((HANDLE) _get_osfhandle (fileno (fp)), 
                                0, 0, FILE_BEGIN);
              return -1;
            }

            numleft -= written;
          }
          FlushFileBuffers ((HANDLE) _get_osfhandle (fileno (fp)));
      }
    }
  return fwrite (buffer, size, count, fp);
}

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