pcre_try_flipped.c

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/*************************************************
*      Perl-Compatible Regular Expressions       *
*************************************************/

/* PCRE is a library of functions to support regular expressions whose syntax
and semantics are as close as possible to those of the Perl 5 language.

                       Written by Philip Hazel
           Copyright (c) 1997-2008 University of Cambridge

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*/


/* This module contains an internal function that tests a compiled pattern to
see if it was compiled with the opposite endianness. If so, it uses an
auxiliary local function to flip the appropriate bytes. */


#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "pcre_internal.h"


/*************************************************
*         Flip bytes in an integer               *
*************************************************/

/* This function is called when the magic number in a regex doesn't match, in
order to flip its bytes to see if we are dealing with a pattern that was
compiled on a host of different endianness. If so, this function is used to
flip other byte values.

Arguments:
  value        the number to flip
  n            the number of bytes to flip (assumed to be 2 or 4)

Returns:       the flipped value
*/

static unsigned long int
byteflip(unsigned long int value, int n)
{
if (n == 2) return ((value & 0x00ff) << 8) | ((value & 0xff00) >> 8);
return ((value & 0x000000ff) << 24) |
       ((value & 0x0000ff00) <<  8) |
       ((value & 0x00ff0000) >>  8) |
       ((value & 0xff000000) >> 24);
}



/*************************************************
*       Test for a byte-flipped compiled regex   *
*************************************************/

/* This function is called from pcre_exec(), pcre_dfa_exec(), and also from
pcre_fullinfo(). Its job is to test whether the regex is byte-flipped - that
is, it was compiled on a system of opposite endianness. The function is called
only when the native MAGIC_NUMBER test fails. If the regex is indeed flipped,
we flip all the relevant values into a different data block, and return it.

Arguments:
  re               points to the regex
  study            points to study data, or NULL
  internal_re      points to a new regex block
  internal_study   points to a new study block

Returns:           the new block if is is indeed a byte-flipped regex
                   NULL if it is not
*/

real_pcre *
_pcre_try_flipped(const real_pcre *re, real_pcre *internal_re,
  const pcre_study_data *study, pcre_study_data *internal_study)
{
if (byteflip(re->magic_number, sizeof(re->magic_number)) != MAGIC_NUMBER)
  return NULL;

*internal_re = *re;           /* To copy other fields */
internal_re->size = byteflip(re->size, sizeof(re->size));
internal_re->options = byteflip(re->options, sizeof(re->options));
internal_re->flags = (pcre_uint16)byteflip(re->flags, sizeof(re->flags));
internal_re->top_bracket =
  (pcre_uint16)byteflip(re->top_bracket, sizeof(re->top_bracket));
internal_re->top_backref =
  (pcre_uint16)byteflip(re->top_backref, sizeof(re->top_backref));
internal_re->first_byte =
  (pcre_uint16)byteflip(re->first_byte, sizeof(re->first_byte));
internal_re->req_byte =
  (pcre_uint16)byteflip(re->req_byte, sizeof(re->req_byte));
internal_re->name_table_offset =
  (pcre_uint16)byteflip(re->name_table_offset, sizeof(re->name_table_offset));
internal_re->name_entry_size =
  (pcre_uint16)byteflip(re->name_entry_size, sizeof(re->name_entry_size));
internal_re->name_count =
  (pcre_uint16)byteflip(re->name_count, sizeof(re->name_count));

if (study != NULL)
  {
  *internal_study = *study;   /* To copy other fields */
  internal_study->size = byteflip(study->size, sizeof(study->size));
  internal_study->options = byteflip(study->options, sizeof(study->options));
  }

return internal_re;
}

/* End of pcre_tryflipped.c */

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