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 32