clang/test/C/C11/n1310.c

   1 // RUN: %clang_cc1 -verify -std=c89 %s
   2 // RUN: %clang_cc1 -verify -std=c99 %s
   3 // RUN: %clang_cc1 -verify -std=c11 %s
   4 // RUN: %clang_cc1 -verify -std=c17 %s
   5 // RUN: %clang_cc1 -verify -std=c23 %s
   6 // expected-no-diagnostics
   7
   8 /* WG14 N1310: Yes
   9  * Requiring signed char to have no padding bits
  10  */
  11
  12 /* This is shockingly hard to test, but we're trying our best by checking that
  13  * setting each bit of an unsigned char, then bit-casting it to signed char,
  14  * results in a value we expect to see. If we have padding bits, then it's
  15  * possible (but not mandatory) for the value to not be as we expect, so a
  16  * failing assertion means the implementation is broken but a passing test does
  17  * not *prove* there aren't padding bits.
  18  */
  19 _Static_assert(__CHAR_BIT__ == 8, "");
  20 _Static_assert(sizeof(signed char) == 1, "");
  21
  22 #define TEST(Bit, Expected) __builtin_bit_cast(signed char, (unsigned char)(1 << Bit)) == Expected
  23 _Static_assert(TEST(0, 1), "");
  24 _Static_assert(TEST(1, 2), "");
  25 _Static_assert(TEST(2, 4), "");
  26 _Static_assert(TEST(3, 8), "");
  27 _Static_assert(TEST(4, 16), "");
  28 _Static_assert(TEST(5, 32), "");
  29 _Static_assert(TEST(6, 64), "");
  30 _Static_assert(TEST(7, (signed char)128), "");
  31