BridgeTC: a bridge from C types to C singleton values

bridgetc_digit_update_1.inc

/* -*- mode: C -*- */
#if BRIDGETC_IMPL_DIGIT_1 == 0
# undef BRIDGETC_IMPL_DIGIT_1
# define BRIDGETC_IMPL_DIGIT_1 1
# undef BRIDGETC_IMPL_SEARCH_1
# define BRIDGETC_IMPL_SEARCH_1 BRIDGETC_IMPL_SEARCH_1_1
#elif BRIDGETC_IMPL_DIGIT_1 == 1
# undef BRIDGETC_IMPL_DIGIT_1
# define BRIDGETC_IMPL_DIGIT_1 2
# undef BRIDGETC_IMPL_SEARCH_1
# define BRIDGETC_IMPL_SEARCH_1 BRIDGETC_IMPL_SEARCH_1_2
#elif BRIDGETC_IMPL_DIGIT_1 == 2
# undef BRIDGETC_IMPL_DIGIT_1
# define BRIDGETC_IMPL_DIGIT_1 3
# undef BRIDGETC_IMPL_SEARCH_1
# define BRIDGETC_IMPL_SEARCH_1 BRIDGETC_IMPL_SEARCH_1_3
#elif BRIDGETC_IMPL_DIGIT_1 == 3
# undef BRIDGETC_IMPL_DIGIT_1
# define BRIDGETC_IMPL_DIGIT_1 4
# undef BRIDGETC_IMPL_SEARCH_1
# define BRIDGETC_IMPL_SEARCH_1 BRIDGETC_IMPL_SEARCH_1_4
#elif BRIDGETC_IMPL_DIGIT_1 == 4
# undef BRIDGETC_IMPL_DIGIT_1
# define BRIDGETC_IMPL_DIGIT_1 5
# undef BRIDGETC_IMPL_SEARCH_1
# define BRIDGETC_IMPL_SEARCH_1 BRIDGETC_IMPL_SEARCH_1_5
#elif BRIDGETC_IMPL_DIGIT_1 == 5
# undef BRIDGETC_IMPL_DIGIT_1
# define BRIDGETC_IMPL_DIGIT_1 6
# undef BRIDGETC_IMPL_SEARCH_1
# define BRIDGETC_IMPL_SEARCH_1 BRIDGETC_IMPL_SEARCH_1_6
#elif BRIDGETC_IMPL_DIGIT_1 == 6
# undef BRIDGETC_IMPL_DIGIT_1
# define BRIDGETC_IMPL_DIGIT_1 7
# undef BRIDGETC_IMPL_SEARCH_1
# define BRIDGETC_IMPL_SEARCH_1 BRIDGETC_IMPL_SEARCH_1_7
#elif BRIDGETC_IMPL_DIGIT_1 == 7
# undef BRIDGETC_IMPL_DIGIT_1
# define BRIDGETC_IMPL_DIGIT_1 8
# undef BRIDGETC_IMPL_SEARCH_1
# define BRIDGETC_IMPL_SEARCH_1 BRIDGETC_IMPL_SEARCH_1_8
#elif BRIDGETC_IMPL_DIGIT_1 == 8
# undef BRIDGETC_IMPL_DIGIT_1
# define BRIDGETC_IMPL_DIGIT_1 9
# undef BRIDGETC_IMPL_SEARCH_1
# define BRIDGETC_IMPL_SEARCH_1 BRIDGETC_IMPL_SEARCH_1_9
#elif BRIDGETC_IMPL_DIGIT_1 == 9
# undef BRIDGETC_IMPL_DIGIT_1
# define BRIDGETC_IMPL_DIGIT_1 0
# undef BRIDGETC_IMPL_SEARCH_1
# define BRIDGETC_IMPL_SEARCH_1 BRIDGETC_IMPL_SEARCH_1_0
# include "bridgetc_digit_update_2.inc"
#endif

bridgetc_digit_update_2.inc

/* -*- mode: C -*- */
#if BRIDGETC_IMPL_DIGIT_2 == 0
# undef BRIDGETC_IMPL_DIGIT_2
# define BRIDGETC_IMPL_DIGIT_2 1
# undef BRIDGETC_IMPL_SEARCH_2
# define BRIDGETC_IMPL_SEARCH_2 BRIDGETC_IMPL_SEARCH_2_1
#elif BRIDGETC_IMPL_DIGIT_2 == 1
# undef BRIDGETC_IMPL_DIGIT_2
# define BRIDGETC_IMPL_DIGIT_2 2
# undef BRIDGETC_IMPL_SEARCH_2
# define BRIDGETC_IMPL_SEARCH_2 BRIDGETC_IMPL_SEARCH_2_2
#elif BRIDGETC_IMPL_DIGIT_2 == 2
# undef BRIDGETC_IMPL_DIGIT_2
# define BRIDGETC_IMPL_DIGIT_2 3
# undef BRIDGETC_IMPL_SEARCH_2
# define BRIDGETC_IMPL_SEARCH_2 BRIDGETC_IMPL_SEARCH_2_3
#elif BRIDGETC_IMPL_DIGIT_2 == 3
# undef BRIDGETC_IMPL_DIGIT_2
# define BRIDGETC_IMPL_DIGIT_2 4
# undef BRIDGETC_IMPL_SEARCH_2
# define BRIDGETC_IMPL_SEARCH_2 BRIDGETC_IMPL_SEARCH_2_4
#elif BRIDGETC_IMPL_DIGIT_2 == 4
# undef BRIDGETC_IMPL_DIGIT_2
# define BRIDGETC_IMPL_DIGIT_2 5
# undef BRIDGETC_IMPL_SEARCH_2
# define BRIDGETC_IMPL_SEARCH_2 BRIDGETC_IMPL_SEARCH_2_5
#elif BRIDGETC_IMPL_DIGIT_2 == 5
# undef BRIDGETC_IMPL_DIGIT_2
# define BRIDGETC_IMPL_DIGIT_2 6
# undef BRIDGETC_IMPL_SEARCH_2
# define BRIDGETC_IMPL_SEARCH_2 BRIDGETC_IMPL_SEARCH_2_6
#elif BRIDGETC_IMPL_DIGIT_2 == 6
# undef BRIDGETC_IMPL_DIGIT_2
# define BRIDGETC_IMPL_DIGIT_2 7
# undef BRIDGETC_IMPL_SEARCH_2
# define BRIDGETC_IMPL_SEARCH_2 BRIDGETC_IMPL_SEARCH_2_7
#elif BRIDGETC_IMPL_DIGIT_2 == 7
# undef BRIDGETC_IMPL_DIGIT_2
# define BRIDGETC_IMPL_DIGIT_2 8
# undef BRIDGETC_IMPL_SEARCH_2
# define BRIDGETC_IMPL_SEARCH_2 BRIDGETC_IMPL_SEARCH_2_8
#elif BRIDGETC_IMPL_DIGIT_2 == 8
# undef BRIDGETC_IMPL_DIGIT_2
# define BRIDGETC_IMPL_DIGIT_2 9
# undef BRIDGETC_IMPL_SEARCH_2
# define BRIDGETC_IMPL_SEARCH_2 BRIDGETC_IMPL_SEARCH_2_9
#elif BRIDGETC_IMPL_DIGIT_2 == 9
# undef BRIDGETC_IMPL_DIGIT_2
# define BRIDGETC_IMPL_DIGIT_2 0
# undef BRIDGETC_IMPL_SEARCH_2
# define BRIDGETC_IMPL_SEARCH_2 BRIDGETC_IMPL_SEARCH_2_0
# error "BTC mapping limit exceeded (999)"
#endif

bridgetc_prologue.h

#pragma once

#define BRIDGETC_IMPL_NEXT BRIDGETC_IMPL_ID(BRIDGETC_IMPL_DIGIT_2, BRIDGETC_IMPL_DIGIT_1, BRIDGETC_IMPL_DIGIT_0)

#define BRIDGETC_IMPL_ID(BTC_V0, BTC_V1, BTC_V2) BRIDGETC_IMPL_ID_(BTC_V0, BTC_V1, BTC_V2)
#define BRIDGETC_IMPL_ID_(BTC_V0, BTC_V1, BTC_V2) BTC_value_##BTC_V0##BTC_V1##BTC_V2

#define BRIDGETC_IMPL_DIGIT_0 0
#define BRIDGETC_IMPL_SEARCH_0(BTC_X, BTC_DEFAULT) BTC_DEFAULT
#define BRIDGETC_IMPL_DIGIT_1 0
#define BRIDGETC_IMPL_SEARCH_1(BTC_X, BTC_DEFAULT) BTC_DEFAULT
#define BRIDGETC_IMPL_DIGIT_2 0
#define BRIDGETC_IMPL_SEARCH_2(BTC_X, BTC_DEFAULT) BTC_DEFAULT

#define BRIDGETC_IMPL_SEARCH(BTC_X, BTC_DEFAULT, ...) \
	BRIDGETC_IMPL_SEARCH_0(BTC_X, \
	BRIDGETC_IMPL_SEARCH_1(BTC_X, \
	BRIDGETC_IMPL_SEARCH_2(BTC_X, BTC_DEFAULT)))

#define BTC_SEARCH(BTC_X, ...) BRIDGETC_IMPL_SEARCH(__typeof__(BTC_X), ##__VA_ARGS__, (void)0)

#define BRIDGETC_IMPL_TEST_0(BTC_X, BTC_V2, BTC_V1, BTC_V0, BTC_DEFAULT)		\
	__builtin_choose_expr(					\
		__builtin_types_compatible_p(BTC_X,			\
			__typeof__(BRIDGETC_IMPL_ID(BTC_V2, BTC_V1, BTC_V0))),	\
		BRIDGETC_IMPL_ID(BTC_V2, BTC_V1, BTC_V0), BTC_DEFAULT)

#define BRIDGETC_IMPL_SEARCH_0_(BTC_X, BTC_V0, BTC_DEFAULT)		\
	BRIDGETC_IMPL_TEST_0(BTC_X, BRIDGETC_IMPL_DIGIT_2, BRIDGETC_IMPL_DIGIT_1, BTC_V0, BTC_DEFAULT)

#define BRIDGETC_IMPL_SEARCH_0_0(BTC_X, BTC_DEFAULT)	\
	BTC_DEFAULT

#define BRIDGETC_IMPL_SEARCH_0_1(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 0,	\
	BTC_DEFAULT)

#define BRIDGETC_IMPL_SEARCH_0_2(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 0,	\
	BTC_DEFAULT))

#define BRIDGETC_IMPL_SEARCH_0_3(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 2,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 0,	\
	BTC_DEFAULT)))

#define BRIDGETC_IMPL_SEARCH_0_4(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 3,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 2,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 0,	\
	BTC_DEFAULT))))

#define BRIDGETC_IMPL_SEARCH_0_5(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 4,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 3,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 2,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 0,	\
	BTC_DEFAULT)))))

#define BRIDGETC_IMPL_SEARCH_0_6(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 5,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 4,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 3,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 2,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 0,	\
	BTC_DEFAULT))))))

#define BRIDGETC_IMPL_SEARCH_0_7(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 6,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 5,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 4,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 3,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 2,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 0,	\
	BTC_DEFAULT)))))))

#define BRIDGETC_IMPL_SEARCH_0_8(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 7,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 6,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 5,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 4,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 3,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 2,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 0,	\
	BTC_DEFAULT))))))))

#define BRIDGETC_IMPL_SEARCH_0_9(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 8,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 7,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 6,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 5,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 4,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 3,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 2,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_0_(BTC_X, 0,	\
	BTC_DEFAULT)))))))))

#define BRIDGETC_IMPL_TEST_1(BTC_X, BTC_V2, BTC_V1, BTC_DEFAULT)	\
	BRIDGETC_IMPL_TEST_0(BTC_X, BTC_V2, BTC_V1, 0,	\
	BRIDGETC_IMPL_TEST_0(BTC_X, BTC_V2, BTC_V1, 1,	\
	BRIDGETC_IMPL_TEST_0(BTC_X, BTC_V2, BTC_V1, 2,	\
	BRIDGETC_IMPL_TEST_0(BTC_X, BTC_V2, BTC_V1, 3,	\
	BRIDGETC_IMPL_TEST_0(BTC_X, BTC_V2, BTC_V1, 4,	\
	BRIDGETC_IMPL_TEST_0(BTC_X, BTC_V2, BTC_V1, 5,	\
	BRIDGETC_IMPL_TEST_0(BTC_X, BTC_V2, BTC_V1, 6,	\
	BRIDGETC_IMPL_TEST_0(BTC_X, BTC_V2, BTC_V1, 7,	\
	BRIDGETC_IMPL_TEST_0(BTC_X, BTC_V2, BTC_V1, 8,	\
	BRIDGETC_IMPL_TEST_0(BTC_X, BTC_V2, BTC_V1, 9,	\
	BTC_DEFAULT))))))))))

#define BRIDGETC_IMPL_SEARCH_1_(BTC_X, BTC_V1, BTC_DEFAULT)		\
	BRIDGETC_IMPL_TEST_1(BTC_X, BRIDGETC_IMPL_DIGIT_2, BTC_V1, BTC_DEFAULT)

#define BRIDGETC_IMPL_SEARCH_1_0(BTC_X, BTC_DEFAULT)	\
	BTC_DEFAULT

#define BRIDGETC_IMPL_SEARCH_1_1(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 0,	\
	BTC_DEFAULT)

#define BRIDGETC_IMPL_SEARCH_1_2(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 0,	\
	BTC_DEFAULT))

#define BRIDGETC_IMPL_SEARCH_1_3(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 2,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 0,	\
	BTC_DEFAULT)))

#define BRIDGETC_IMPL_SEARCH_1_4(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 3,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 2,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 0,	\
	BTC_DEFAULT))))

#define BRIDGETC_IMPL_SEARCH_1_5(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 4,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 3,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 2,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 0,	\
	BTC_DEFAULT)))))

#define BRIDGETC_IMPL_SEARCH_1_6(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 5,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 4,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 3,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 2,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 0,	\
	BTC_DEFAULT))))))

#define BRIDGETC_IMPL_SEARCH_1_7(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 6,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 5,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 4,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 3,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 2,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 0,	\
	BTC_DEFAULT)))))))

#define BRIDGETC_IMPL_SEARCH_1_8(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 7,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 6,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 5,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 4,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 3,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 2,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 0,	\
	BTC_DEFAULT))))))))

#define BRIDGETC_IMPL_SEARCH_1_9(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 8,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 7,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 6,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 5,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 4,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 3,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 2,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_1_(BTC_X, 0,	\
	BTC_DEFAULT)))))))))

#define BRIDGETC_IMPL_TEST_2(BTC_X, BTC_V2, BTC_DEFAULT)	\
	BRIDGETC_IMPL_TEST_1(BTC_X, BTC_V2, 0,	\
	BRIDGETC_IMPL_TEST_1(BTC_X, BTC_V2, 1,	\
	BRIDGETC_IMPL_TEST_1(BTC_X, BTC_V2, 2,	\
	BRIDGETC_IMPL_TEST_1(BTC_X, BTC_V2, 3,	\
	BRIDGETC_IMPL_TEST_1(BTC_X, BTC_V2, 4,	\
	BRIDGETC_IMPL_TEST_1(BTC_X, BTC_V2, 5,	\
	BRIDGETC_IMPL_TEST_1(BTC_X, BTC_V2, 6,	\
	BRIDGETC_IMPL_TEST_1(BTC_X, BTC_V2, 7,	\
	BRIDGETC_IMPL_TEST_1(BTC_X, BTC_V2, 8,	\
	BRIDGETC_IMPL_TEST_1(BTC_X, BTC_V2, 9,	\
	BTC_DEFAULT))))))))))

#define BRIDGETC_IMPL_SEARCH_2_(BTC_X, BTC_V2, BTC_DEFAULT)		\
	BRIDGETC_IMPL_TEST_2(BTC_X, BTC_V2, BTC_DEFAULT)

#define BRIDGETC_IMPL_SEARCH_2_0(BTC_X, BTC_DEFAULT)	\
	BTC_DEFAULT

#define BRIDGETC_IMPL_SEARCH_2_1(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 0,	\
	BTC_DEFAULT)

#define BRIDGETC_IMPL_SEARCH_2_2(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 0,	\
	BTC_DEFAULT))

#define BRIDGETC_IMPL_SEARCH_2_3(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 2,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 0,	\
	BTC_DEFAULT)))

#define BRIDGETC_IMPL_SEARCH_2_4(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 3,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 2,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 0,	\
	BTC_DEFAULT))))

#define BRIDGETC_IMPL_SEARCH_2_5(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 4,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 3,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 2,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 0,	\
	BTC_DEFAULT)))))

#define BRIDGETC_IMPL_SEARCH_2_6(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 5,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 4,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 3,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 2,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 0,	\
	BTC_DEFAULT))))))

#define BRIDGETC_IMPL_SEARCH_2_7(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 6,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 5,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 4,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 3,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 2,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 0,	\
	BTC_DEFAULT)))))))

#define BRIDGETC_IMPL_SEARCH_2_8(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 7,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 6,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 5,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 4,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 3,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 2,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 0,	\
	BTC_DEFAULT))))))))

#define BRIDGETC_IMPL_SEARCH_2_9(BTC_X, BTC_DEFAULT)	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 8,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 7,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 6,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 5,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 4,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 3,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 2,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 1,	\
	BRIDGETC_IMPL_SEARCH_2_(BTC_X, 0,	\
	BTC_DEFAULT)))))))))

bridgetc_register.inc

/* -*- mode: C -*- */
#include "bridgetc_prologue.h"

#pragma GCC diagnostic push
#ifndef __clang__
# pragma GCC diagnostic ignored "-Wold-style-declaration"
#endif

} static const __attribute__((__unused__)) BRIDGETC_IMPL_NEXT;

#pragma GCC diagnostic pop
_Static_assert(__builtin_types_compatible_p(void,	\
	__typeof__(BTC_SEARCH(BRIDGETC_IMPL_NEXT))),	\
	"Only one singleton may be associated with each type.");

static __typeof__(BRIDGETC_IMPL_NEXT) BRIDGETC_IMPL_NEXT = {

#if BRIDGETC_IMPL_DIGIT_0 == 0
# undef BRIDGETC_IMPL_DIGIT_0
# define BRIDGETC_IMPL_DIGIT_0 1
# undef BRIDGETC_IMPL_SEARCH_0
# define BRIDGETC_IMPL_SEARCH_0 BRIDGETC_IMPL_SEARCH_0_1
#elif BRIDGETC_IMPL_DIGIT_0 == 1
# undef BRIDGETC_IMPL_DIGIT_0
# define BRIDGETC_IMPL_DIGIT_0 2
# undef BRIDGETC_IMPL_SEARCH_0
# define BRIDGETC_IMPL_SEARCH_0 BRIDGETC_IMPL_SEARCH_0_2
#elif BRIDGETC_IMPL_DIGIT_0 == 2
# undef BRIDGETC_IMPL_DIGIT_0
# define BRIDGETC_IMPL_DIGIT_0 3
# undef BRIDGETC_IMPL_SEARCH_0
# define BRIDGETC_IMPL_SEARCH_0 BRIDGETC_IMPL_SEARCH_0_3
#elif BRIDGETC_IMPL_DIGIT_0 == 3
# undef BRIDGETC_IMPL_DIGIT_0
# define BRIDGETC_IMPL_DIGIT_0 4
# undef BRIDGETC_IMPL_SEARCH_0
# define BRIDGETC_IMPL_SEARCH_0 BRIDGETC_IMPL_SEARCH_0_4
#elif BRIDGETC_IMPL_DIGIT_0 == 4
# undef BRIDGETC_IMPL_DIGIT_0
# define BRIDGETC_IMPL_DIGIT_0 5
# undef BRIDGETC_IMPL_SEARCH_0
# define BRIDGETC_IMPL_SEARCH_0 BRIDGETC_IMPL_SEARCH_0_5
#elif BRIDGETC_IMPL_DIGIT_0 == 5
# undef BRIDGETC_IMPL_DIGIT_0
# define BRIDGETC_IMPL_DIGIT_0 6
# undef BRIDGETC_IMPL_SEARCH_0
# define BRIDGETC_IMPL_SEARCH_0 BRIDGETC_IMPL_SEARCH_0_6
#elif BRIDGETC_IMPL_DIGIT_0 == 6
# undef BRIDGETC_IMPL_DIGIT_0
# define BRIDGETC_IMPL_DIGIT_0 7
# undef BRIDGETC_IMPL_SEARCH_0
# define BRIDGETC_IMPL_SEARCH_0 BRIDGETC_IMPL_SEARCH_0_7
#elif BRIDGETC_IMPL_DIGIT_0 == 7
# undef BRIDGETC_IMPL_DIGIT_0
# define BRIDGETC_IMPL_DIGIT_0 8
# undef BRIDGETC_IMPL_SEARCH_0
# define BRIDGETC_IMPL_SEARCH_0 BRIDGETC_IMPL_SEARCH_0_8
#elif BRIDGETC_IMPL_DIGIT_0 == 8
# undef BRIDGETC_IMPL_DIGIT_0
# define BRIDGETC_IMPL_DIGIT_0 9
# undef BRIDGETC_IMPL_SEARCH_0
# define BRIDGETC_IMPL_SEARCH_0 BRIDGETC_IMPL_SEARCH_0_9
#elif BRIDGETC_IMPL_DIGIT_0 == 9
# undef BRIDGETC_IMPL_DIGIT_0
# define BRIDGETC_IMPL_DIGIT_0 0
# undef BRIDGETC_IMPL_SEARCH_0
# define BRIDGETC_IMPL_SEARCH_0 BRIDGETC_IMPL_SEARCH_0_0
# include "bridgetc_digit_update_1.inc"
#endif

generator.py

#!/usr/bin/env python3
# Generator for type singletons in C.
#
# Let's say you have a data structure with some extensible behaviour
# (e.g., user-defined hashing and equality testing functions).  One
# might use a vtable, but, in most cases, the calling code isn't
# late-bound: while containers might be type-generic, their users
# rarely are, in C.
#
# Ideally, we would have something like a vtable, except without any
# per-instance space usage overhead, and, ideally, transparent enough
# for C compilers to optimise away the indirection.
#
# That's what B(ridge)TC provides: a way to encode references to C
# variables in *C types*, and a conversion back from these types to
# the variables' values, all optimised away at compile-time.
#
# With apologies to Helen Fielding and her famous singleton, Bridget.

# The generator, as well as its output, is MIT Licensed.
#
# Copyright 2020 Paul Khuong
#
# Permission is hereby granted, free of charge, to any person
# obtaining a copy of this software and associated documentation files
# (the "Software"), to deal in the Software without restriction,
# including without limitation the rights to use, copy, modify, merge,
# publish, distribute, sublicense, and/or sell copies of the Software,
# and to permit persons to whom the Software is furnished to do so,
# subject to the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.

FILE_PREFIX = "bridgetc"

IMPL = "BRIDGETC_IMPL"

NS = "BTC"

# We increment in CPP by storing different digits in different
# variables, and updating each with an #if ladder.

# Spread our state across 3 variables, which lets us count to 998
# (there's an off by one that's not worth fixing).
NUM_DIGITS = 3

# And count in radix 10; make this lower to have an easier time
# testing higher digit counts.
RADIX = 10

assert RADIX <= 10, "Pasting digits stops working above 10"

IDENTIFIERS = [f"{NS}_V{i}" for i in range(NUM_DIGITS)]

DIGIT_VARS = [f"{IMPL}_DIGIT_{i}" for i in range(NUM_DIGITS)]


def enumerate_search_cases(digit, out):
    acc = f"{NS}_DEFAULT"
    for i in range(RADIX):
        print(
            f"""\
#define {IMPL}_SEARCH_{digit}_{i}({NS}_X, {NS}_DEFAULT)	\\
	{acc}
""",
            file=out,
        )
        acc = f"{IMPL}_SEARCH_{digit}_({NS}_X, {i},\t\\\n\t{acc})"


def generate_prologue(path=f"{FILE_PREFIX}_prologue.h"):
    id_list = ", ".join(IDENTIFIERS)
    with open(path, "w") as out:
        print(
            f"""\
#pragma once

#define {IMPL}_NEXT {IMPL}_ID({", ".join(reversed(DIGIT_VARS))})

#define {IMPL}_ID({id_list}) {IMPL}_ID_({id_list})
#define {IMPL}_ID_({id_list}) {NS}_value_##{"##".join(IDENTIFIERS)}
""",
            file=out,
        )

        for i in range(NUM_DIGITS):
            print(f"#define {IMPL}_DIGIT_{i} 0", file=out)
            print(
                f"#define {IMPL}_SEARCH_{i}({NS}_X, {NS}_DEFAULT) {NS}_DEFAULT",
                file=out,
            )

        # The __builtin_types_compatible_p implementation needs to
        # nest these search macros.  The implementation is a bit nicer
        # with _Generic.
        search_expr = (
            "\\\n\t".join(f"{IMPL}_SEARCH_{i}({NS}_X, " for i in range(NUM_DIGITS))
            + f"{NS}_DEFAULT"
            + NUM_DIGITS * ")"
        )
        print(
            f"""
#define {IMPL}_SEARCH({NS}_X, {NS}_DEFAULT, ...) \\
	{search_expr}

#define {NS}_SEARCH({NS}_X, ...) {IMPL}_SEARCH(__typeof__({NS}_X), ##__VA_ARGS__, (void)0)
""",
            file=out,
        )

        # Base case for the __builtin_types_compatible_p search.
        rident = ", ".join(reversed(IDENTIFIERS))
        digits = list(reversed(DIGIT_VARS[1:]))
        var = IDENTIFIERS[0]
        print(
            f"""\
#define {IMPL}_TEST_0({NS}_X, {rident}, {NS}_DEFAULT)		\\
	__builtin_choose_expr(					\\
		__builtin_types_compatible_p({NS}_X,			\\
			__typeof__({IMPL}_ID({rident}))),	\\
		{IMPL}_ID({rident}), {NS}_DEFAULT)

#define {IMPL}_SEARCH_0_({NS}_X, {var}, {NS}_DEFAULT)		\\
	{IMPL}_TEST_0({NS}_X, {", ".join(digits + [var])}, {NS}_DEFAULT)
""",
            file=out,
        )

        enumerate_search_cases(0, out)

        for i in range(1, NUM_DIGITS):
            variant = list(reversed(IDENTIFIERS[i:]))
            digits = list(reversed(DIGIT_VARS[i + 1 :]))
            var = IDENTIFIERS[i]
            prev_test = f"{IMPL}_TEST_{i - 1}"
            acc = f"{NS}_DEFAULT"

            for enumerated in reversed(range(RADIX)):
                args = ", ".join(variant + [str(enumerated)])
                acc = f"{prev_test}({NS}_X, {args},\t\\\n\t{acc})"
            print(
                f"""\
#define {IMPL}_TEST_{i}({NS}_X, {", ".join(variant)}, {NS}_DEFAULT)	\\
	{acc}

#define {IMPL}_SEARCH_{i}_({NS}_X, {var}, {NS}_DEFAULT)		\\
	{IMPL}_TEST_{i}({NS}_X, {", ".join(digits + [var])}, {NS}_DEFAULT)
""",
                file=out,
            )

            enumerate_search_cases(i, out)


generate_prologue()


def generate_digit_update(digit, out):
    var = f"{IMPL}_DIGIT_{digit}"
    search = f"{IMPL}_SEARCH_{digit}"
    conditional = "if"
    for i in range(RADIX):
        succ = (i + 1) % RADIX
        print(
            f"""\
#{conditional} {var} == {i}
# undef {var}
# define {var} {succ}
# undef {search}
# define {search} {search}_{succ}\
""",
            file=out,
        )
        conditional = "elif"
    next_digit = digit + 1
    if next_digit == NUM_DIGITS:
        print(
            f"""# error "BTC mapping limit exceeded ({RADIX ** NUM_DIGITS - 1})"\
""",
            file=out,
        )
    else:
        print(
            f"""# include "{FILE_PREFIX}_digit_update_{next_digit}.inc"\
""",
            file=out,
        )
    print("#endif", file=out)


for digit in range(1, NUM_DIGITS):
    with open(f"{FILE_PREFIX}_digit_update_{digit}.inc", "w") as out:
        print("/* -*- mode: C -*- */", file=out)
        generate_digit_update(digit, out)


def generate_register(out):
    print(
        f"""\
/* -*- mode: C -*- */
#include "{FILE_PREFIX}_prologue.h"

#pragma GCC diagnostic push
#ifndef __clang__
# pragma GCC diagnostic ignored "-Wold-style-declaration"
#endif

}} static const __attribute__((__unused__)) {IMPL}_NEXT;

#pragma GCC diagnostic pop
_Static_assert(__builtin_types_compatible_p(void,	\\
	__typeof__({NS}_SEARCH({IMPL}_NEXT))),	\\
	"Only one singleton may be associated with each type.");

static __typeof__({IMPL}_NEXT) {IMPL}_NEXT = {{
""",
        file=out,
    )
    generate_digit_update(0, out)


with open(f"{FILE_PREFIX}_register.inc", "w") as out:
    generate_register(out)

test.c

struct foo {
        int x;
#include "bridgetc_register.inc"
        .x = 42,
};

struct bar {
        double x;
#include "bridgetc_register.inc"
        .x = 1.5,
};

int
test_foo()
{
        struct {
                __attribute__((packed)) struct foo tag[0];
                char v;
        } test;

        return BTC_SEARCH(test.tag[0]).x;
}

test.expanded

# gcc -E -W -Wall -O test.c -o - | grep -v '^#' | clang-format-4.0 
struct foo {
  int x;

} static const __attribute__((__unused__)) BTC_value_000;

_Static_assert(__builtin_types_compatible_p(void, __typeof__((void)0)),
               "Only one singleton may be associated with each type.");

static __typeof__(BTC_value_000) BTC_value_000 = {
    .x = 42,
};

struct bar {
  double x;

} static const __attribute__((__unused__)) BTC_value_001;

_Static_assert(__builtin_types_compatible_p(
                   void,
                   __typeof__(__builtin_choose_expr(
                       __builtin_types_compatible_p(__typeof__(BTC_value_001),
                                                    __typeof__(BTC_value_000)),
                       BTC_value_000, (void)0))),
               "Only one singleton may be associated with each type.");

static __typeof__(BTC_value_001) BTC_value_001 = {
    .x = 1.5,
};

int test_foo() {
  struct {
    __attribute__((packed)) struct foo tag[0];
    char v;
  } test;

  return __builtin_choose_expr(
             __builtin_types_compatible_p(__typeof__(test.tag[0]),
                                          __typeof__(BTC_value_001)),
             BTC_value_001,
             __builtin_choose_expr(
                 __builtin_types_compatible_p(__typeof__(test.tag[0]),
                                              __typeof__(BTC_value_000)),
                 BTC_value_000, (void)0))
      .x;
}

test.s

        .file   "test.c"
        .text
        .globl  test_foo
        .type   test_foo, @function
test_foo:
.LFB0:
        .cfi_startproc
        movl    $42, %eax
        ret
        .cfi_endproc
.LFE0:
        .size   test_foo, .-test_foo
        .ident  "GCC: (Debian 6.3.0-18+deb9u1) 6.3.0 20170516"
        .section        .note.GNU-stack,"",@progbits