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[C11] Add test coverage for N1310 and claim conformance

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This is about the best I could do for testing that `signed char` does
not have any padding bits.
This commit is contained in:
Aaron Ballman 2024-03-20 15:07:23 -04:00
parent 2e817bfb48
commit 7955bde64e
2 changed files with 32 additions and 1 deletions
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31
clang/test/C/C11/n1310.c Normal file
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@ -0,0 +1,31 @@
// RUN: %clang_cc1 -verify -std=c89 %s
// RUN: %clang_cc1 -verify -std=c99 %s
// RUN: %clang_cc1 -verify -std=c11 %s
// RUN: %clang_cc1 -verify -std=c17 %s
// RUN: %clang_cc1 -verify -std=c23 %s
// expected-no-diagnostics
/* WG14 N1310: Yes
* Requiring signed char to have no padding bits
*/
/* This is shockingly hard to test, but we're trying our best by checking that
* setting each bit of an unsigned char, then bit-casting it to signed char,
* results in a value we expect to see. If we have padding bits, then it's
* possible (but not mandatory) for the value to not be as we expect, so a
* failing assertion means the implementation is broken but a passing test does
* not *prove* there aren't padding bits.
*/
_Static_assert(__CHAR_BIT__ == 8, "");
_Static_assert(sizeof(signed char) == 1, "");
#define TEST(Bit, Expected) __builtin_bit_cast(signed char, (unsigned char)(1 << Bit)) == Expected
_Static_assert(TEST(0, 1), "");
_Static_assert(TEST(1, 2), "");
_Static_assert(TEST(2, 4), "");
_Static_assert(TEST(3, 8), "");
_Static_assert(TEST(4, 16), "");
_Static_assert(TEST(5, 32), "");
_Static_assert(TEST(6, 64), "");
_Static_assert(TEST(7, (signed char)128), "");

2
clang/www/c_status.html
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@ -411,7 +411,7 @@ conformance.</p>
<tr>
<td>Requiring signed char to have no padding bits</td>
<td><a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1310.htm">N1310</a></td>
<td class="unknown" align="center">Unknown</td>
<td class="full" align="center">Yes</td>
</tr>
<tr>
<td>Initializing static or external variables</td>