libc/stdio/_adjust_pos.c

   1 /* Copyright (C) 2004       Manuel Novoa III    <mjn3@codepoet.org>
   2  *
   3  * GNU Library General Public License (LGPL) version 2 or later.
   4  *
   5  * Dedicated to Toni.  See uClibc/DEDICATION.mjn3 for details.
   6  */
   7
   8 #include "_stdio.h"
   9
  10 /* Both ftell() and fseek() (for SEEK_CUR) need to correct the stream's
  11  * position to take into account buffered data and ungotten chars.
  12  *
  13  * If successful, store corrected position in *pos and return >= 0.
  14  * Otherwise return < 0.
  15  *
  16  * If position is unrepresentable, set errno to EOVERFLOW.
  17  */
  18
  19 int attribute_hidden __stdio_adjust_position(register FILE * __restrict stream,
  20                                                         register __offmax_t *pos)
  21 {
  22         __offmax_t oldpos;
  23         int corr;
  24
  25         if ((corr = stream->__modeflags & __MASK_READING) != 0) {
  26                 --corr; /* Correct for ungots. Assume narrow, and fix below. */
  27         }
  28
  29 #ifdef __UCLIBC_HAS_WCHAR__
  30         if (corr && __STDIO_STREAM_IS_WIDE(stream)) {
  31                 /* A wide stream and we have at least one ungotten wchar.
  32                  * If it is a user ungot, we need to fail since position
  33                  * is unspecified as per C99. */
  34                 if ((corr > 1) || stream->__ungot[1]) { /* User ungetwc, */
  35                         return -1;                      /* so position is undefined. */
  36                 }
  37                 corr -= (1 + stream->__ungot_width[1]);
  38                 if (stream->__state.__mask > 0) { /* Incomplete (bad?) mb char. */
  39                         corr -= stream->__ungot_width[0];
  40                 }
  41         }
  42 #endif
  43
  44 #ifdef __STDIO_BUFFERS
  45         corr += (((__STDIO_STREAM_IS_WRITING(stream))
  46                           ? stream->__bufstart : stream->__bufread)
  47                          - stream->__bufpos);
  48 #endif
  49
  50         oldpos = *pos;
  51
  52         /* Range checking cases:
  53          * (pos - corr >  pos) && (corr >  0) : underflow?  return -corr < 0
  54          * (pos - corr >  pos) && (corr <  0) : ok .. return -corr > 0
  55          * (pos - corr <= pos) && (corr >= 0) : ok .. return  corr > 0
  56          * (pos - corr <= pos) && (corr <  0) : overflow ..  return corr < 0
  57          */
  58
  59         if ((*pos -= corr) > oldpos) {
  60                 corr = -corr;
  61         }
  62
  63         if (corr < 0) {
  64                 __set_errno(EOVERFLOW);
  65         }
  66
  67         return corr;
  68 }