coreboot
coreboot is an Open Source project aimed at replacing the proprietary BIOS found in most computers.
base3.h
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1 /* SPDX-License-Identifier: GPL-2.0-only */
2 
3 #ifndef __SRC_INCLUDE_BASE3_H__
4 #define __SRC_INCLUDE_BASE3_H__
5 
6 /* We translate a floating pin (Z) as the ternary digit 2. */
7 #define Z 2
8 
9 /*
10  * This provides a variadic macro BASE3() that can be used to translate a set of
11  * pin states into its base-3 integer representation, even in the context of a
12  * static initializer. You can call it with any number of up to 6 arguments,
13  * e.g. BASE3(1, Z) -> 5 or BASE3(0, Z, 1, 0) -> 21. Just don't look too closely
14  * at how the sausage is made. (Pay extra attention to typos when expanding it!)
15  */
16 #define _BASE3_IMPL_1(arg0, arg1, arg2, arg3, arg4, arg5) arg0
17 #define _BASE3_IMPL_2(arg0, arg1, arg2, arg3, arg4, arg5) \
18  (arg1 + (3 * _BASE3_IMPL_1(arg0, arg1, arg2, arg3, arg4, arg5)))
19 #define _BASE3_IMPL_3(arg0, arg1, arg2, arg3, arg4, arg5) \
20  (arg2 + (3 * _BASE3_IMPL_2(arg0, arg1, arg2, arg3, arg4, arg5)))
21 #define _BASE3_IMPL_4(arg0, arg1, arg2, arg3, arg4, arg5) \
22  (arg3 + (3 * _BASE3_IMPL_3(arg0, arg1, arg2, arg3, arg4, arg5)))
23 #define _BASE3_IMPL_5(arg0, arg1, arg2, arg3, arg4, arg5) \
24  (arg4 + (3 * _BASE3_IMPL_4(arg0, arg1, arg2, arg3, arg4, arg5)))
25 #define _BASE3_IMPL_6(arg0, arg1, arg2, arg3, arg4, arg5) \
26  (arg5 + (3 * _BASE3_IMPL_5(arg0, arg1, arg2, arg3, arg4, arg5)))
27 #define _BASE3_IMPL(arg0, arg1, arg2, arg3, arg4, arg5, NARGS, ...) \
28  _BASE3_IMPL##NARGS(arg0, arg1, arg2, arg3, arg4, arg5)
29 #define BASE3(...) _BASE3_IMPL(__VA_ARGS__, _6, _5, _4, _3, _2, _1)
30 
31 #endif /* __SRC_INCLUDE_BASE3_H__ */