[PATCH] Use correct signedness in wcsncmp.

[Stefan Liebler <stli at linux dot vnet dot ibm dot com>]

Hi,

the wcsncmp implementation does not behave the same as wcscmp
and wmemcmp due to using substraction instead of comparision:

wchar_t w0[] = { WCHAR_MIN, 0 };
wchar_t w1[] = { WCHAR_MAX, 0 };

wcscmp (w0, w1) = -1
wcsncmp (w0, w1, 2) = 1
wmemcmp (w0, w1, 2) = -1


This patch adjusts wcsncmp behavior in the same way,
as it was done for wcscmp and wmemcmp:
-"Use correct signedness in default implementations of wcscmp and wmemcmp"
(https://sourceware.org/git/?p=glibc.git;a=commit;h=1f1e194720177de3cbc2a84bc62d22e63cb23d4a)

-"Fix signedness in wcscmp comparison"
(https://sourceware.org/git/?p=glibc.git;a=commit;h=95584d3b3309ff4da4cc458254df383f5cff044b)

The testcase localedata/tests-mbwc/tst_wcsncmp.c expects the exact
character difference, therefore it is adjusted in the same way as
"wcscmp testsuite too strict"
(https://sourceware.org/ml/libc-alpha/2000-10/msg00001.html).

The testcase string/test-strncmp.c now supports testing wcsncmp if WIDE
is defined. The corresponding testcase wcsmbs/test-wcsncmp.c is added.

Tested on s390x and x86_64.

Ok to commit?

Bye
Stefan

---
2015-03-26  Stefan Liebler  <stli@linux.vnet.ibm.com>

	* wcsmbs/wcsncmp.c (wcsncmp): Compare as wchar_t, not wint_t.
	  Use signed comparision instead of substraction to avoid
	  overflow bug.
	* localedata/tests-mbwc/tst_wcsncmp.c (tst_wcsncmp):
	  Take the sign of ret.
	* localedata/tests-mbwc/dat_wcsncmp.c (tst_wcsncmp_loc):
	  DonÂt expect precise return values. Only the sign matters.
	* wcsmbs/Makefile (strop-tests): Add wcsncmp.
	* wcsmbs/test-wcsncmp.c: New File.
	* string/test-strncmp.c: Add wcsncmp support.

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