Last active
July 24, 2023 00:40
-
-
Save imaami/43e96d243b21d873a23fda0c6267a89c to your computer and use it in GitHub Desktop.
Type information-encoded flags in C
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
#include <stdio.h> | |
enum { | |
FOO = 1 << 0, | |
BAR = 1 << 1, | |
BYX = 1 << 2, | |
QUE = 1 << 3 | |
}; | |
#define maybe_signed(T, cond) __typeof__( \ | |
_Generic(&(char[2 - !(cond)]){0}, \ | |
char(*)[1]: (unsigned T)0, \ | |
char(*)[2]: (signed T)0)) | |
#define if_signed(T, x, then) \ | |
_Generic((__typeof__(x) *){0}, \ | |
signed T const *: (then), unsigned T *: 0, \ | |
signed T *: (then), unsigned T const *: 0) | |
#define define_metaflag(flag, flags) \ | |
maybe_signed(char, flag & (flags)) meta_##flag | |
#define decode_metaflag(T, flag) \ | |
if_signed(char, (T){0}.meta_##flag, flag) | |
#define define_metamap(T, flags) \ | |
typedef union { \ | |
define_metaflag(FOO, flags); \ | |
define_metaflag(BAR, flags); \ | |
define_metaflag(BYX, flags); \ | |
define_metaflag(QUE, flags); \ | |
} T | |
#define decode_metamap(T) ( \ | |
0u | decode_metaflag(T, FOO) \ | |
| decode_metaflag(T, BAR) \ | |
| decode_metaflag(T, BYX) \ | |
| decode_metaflag(T, QUE) \ | |
) | |
int main (void) | |
{ | |
define_metamap(foo_and_byx, FOO | BYX); | |
define_metamap(bar_and_que, BAR | QUE); | |
define_metamap(without_foo, BAR | BYX | QUE); | |
printf("0x%04x\n0x%04x\n0x%04x\n", | |
decode_metamap(foo_and_byx), | |
decode_metamap(bar_and_que), | |
decode_metamap(without_foo)); | |
} |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment