tolower.c

/*
FUNCTION
	<<tolower>>, <<tolower_l>>---translate characters to lowercase

INDEX
	tolower

INDEX
	tolower_l

INDEX
	_tolower

SYNOPSIS
	#include <ctype.h>
	int tolower(int <[c]>);
	int _tolower(int <[c]>);

	#include <ctype.h>
	int tolower_l(int <[c]>, locale_t <[locale]>);


DESCRIPTION
<<tolower>> is a macro which converts uppercase characters to lowercase,
leaving all other characters unchanged.  It is only defined when
<[c]> is an integer in the range <<EOF>> to <<255>>.

<<tolower_l>> is like <<tolower>> but performs the function based on the
locale specified by the locale object locale.  If <[locale]> is
LC_GLOBAL_LOCALE or not a valid locale object, the behaviour is undefined.

You can use a compiled subroutine instead of the macro definition by
undefining this macro using `<<#undef tolower>>' or `<<#undef tolower_l>>'.

<<_tolower>> performs the same conversion as <<tolower>>, but should
only be used when <[c]> is known to be an uppercase character (<<A>>--<<Z>>).

RETURNS
<<tolower>>, <<tolower_l>> return the lowercase equivalent of <[c]> when
<[c]> is an uppercase character, and <[c]> otherwise.

<<_tolower>> returns the lowercase equivalent of <[c]> when it is a
character between <<A>> and <<Z>>.  If <[c]> is not one of these
characters, the behaviour of <<_tolower>> is undefined.

PORTABILITY
<<tolower>> is ANSI C.  <<_tolower>> is not recommended for portable programs.
<<tolower_l>> is POSIX-1.2008.

No supporting OS subroutines are required.
*/ 

#include <_ansi.h>
#include <ctype.h>
#if defined (_MB_EXTENDED_CHARSETS_ISO) || defined (_MB_EXTENDED_CHARSETS_WINDOWS)
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <wctype.h>
#include <wchar.h>
#endif

#undef tolower
int
tolower (int c)
{
#if defined (_MB_EXTENDED_CHARSETS_ISO) || defined (_MB_EXTENDED_CHARSETS_WINDOWS)
  if ((unsigned char) c <= 0x7f) 
    return isupper (c) ? c - 'A' + 'a' : c;
  else if (c != EOF && MB_CUR_MAX == 1 && isupper (c))
    {
      char s[MB_LEN_MAX] = { c, '\0' };
      wchar_t wc;
      if (mbtowc (&wc, s, 1) >= 0
	  && wctomb (s, (wchar_t) towlower ((wint_t) wc)) == 1)
	c = (unsigned char) s[0];
    }
  return c;
#else
  return isupper(c) ? (c) - 'A' + 'a' : c;
#endif
}