path: root/shared/c-stdaux/src/c-stdaux.h

#pragma once

/*
 * Auxiliary macros and functions for the C standard library
 *
 * The `c-stdaux.h` header contains a collection of auxiliary macros and helper
 * functions around the functionality provided by the different C standard
 * library implementations, as well as other specifications implemented by
 * them.
 *
 * Most of the helpers provided here provide aliases for common library and
 * compiler features. Furthermore, several helpers simply provide other calling
 * conventions than their standard counterparts (e.g., they allow for NULL to
 * be passed with an object length of 0 where it makes sense to accept empty
 * input).
 *
 * The namespace used by this project is:
 *
 *  * `c_*` for all common C symbols or definitions that behave like proper C
 *    entities (e.g., macros that protect against double-evaluation would use
 *    lower-case names)
 *
 *  * `C_*` for all constants, as well as macros that may not be safe against
 *    double evaluation.
 */

#ifdef __cplusplus
extern "C" {
#endif

#include <assert.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <inttypes.h>
#include <limits.h>
#include <stdalign.h>
#include <stdarg.h>
#if 0 /* NM_IGNORED */
#include <stdatomic.h>
#endif /* NM_IGNORED */
#include <stdbool.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdnoreturn.h>
#include <string.h>
#include <sys/time.h>
#include <sys/types.h>
#include <time.h>
#include <unistd.h>

/*
 * Shortcuts for gcc attributes. See GCC manual for details. They're 1-to-1
 * mappings to the GCC equivalents. No additional magic here. They are
 * supported by other compilers as well.
 */
#define _c_cleanup_(_x) __attribute__((__cleanup__(_x)))
#define _c_const_ __attribute__((__const__))
#define _c_deprecated_ __attribute__((__deprecated__))
#define _c_hidden_ __attribute__((__visibility__("hidden")))
#define _c_likely_(_x) (__builtin_expect(!!(_x), 1))
#define _c_packed_ __attribute__((__packed__))
#define _c_printf_(_a, _b) __attribute__((__format__(printf, _a, _b)))
#define _c_public_ __attribute__((__visibility__("default")))
#define _c_pure_ __attribute__((__pure__))
#define _c_sentinel_ __attribute__((__sentinel__))
#define _c_unlikely_(_x) (__builtin_expect(!!(_x), 0))
#define _c_unused_ __attribute__((__unused__))

/**
 * C_EXPR_ASSERT() - create expression with assertion
 * @_expr:              expression to evaluate to
 * @_assertion:         arbitrary assertion
 * @_message:           message associated with the assertion
 *
 * This macro simply evaluates to @_expr. That is, it can be used in any
 * context that expects an expression like @_expr. Additionally, it takes an
 * assertion as @_assertion and evaluates it through _Static_assert(), using
 * @_message as debug message.
 *
 * The _Static_assert() builtin of C11 is defined as statement and thus cannot
 * be used in expressions. This macro circumvents this restriction.
 *
 * Return: Evaluates to @_expr.
 */
#define C_EXPR_ASSERT(_expr, _assertion, _message)                      \
        /* indentation and line-split to get better diagnostics */      \
        (__builtin_choose_expr(                                         \
                !!(1 + 0 * sizeof(                                      \
                        struct {                                        \
_Static_assert(_assertion, _message); \
                        }                                               \
                )),                                                     \
                (_expr),                                                \
                ((void)0)                                               \
        ))

/**
 * C_STRINGIFY() - stringify a token, but evaluate it first
 * @_x:         token to evaluate and stringify
 *
 * Return: Evaluates to a constant string literal
 */
#define C_STRINGIFY(_x) C_INTERNAL_STRINGIFY(_x)
#define C_INTERNAL_STRINGIFY(_x) #_x

/**
 * C_CONCATENATE() - concatenate two tokens, but evaluate them first
 * @_x:         first token
 * @_y:         second token
 *
 * Return: Evaluates to a constant identifier
 */
#define C_CONCATENATE(_x, _y) C_INTERNAL_CONCATENATE(_x, _y)
#define C_INTERNAL_CONCATENATE(_x, _y) _x ## _y

/**
 * C_EXPAND() - expand a tuple to a series of its values
 * @_x:         tuple to expand
 *
 * Return: Evaluates to the expanded tuple
 */
#define C_EXPAND(_x) C_INTERNAL_EXPAND _x
#define C_INTERNAL_EXPAND(...) __VA_ARGS__

/**
 * C_VAR() - generate unique variable name
 * @_x:         name of variable, optional
 * @_uniq:      unique prefix, usually provided by __COUNTER__, optional
 *
 * This macro shall be used to generate unique variable names, that will not be
 * shadowed by recursive macro invocations. It is effectively a
 * C_CONCATENATE of both arguments, but also provides a globally separated
 * prefix and makes the code better readable.
 *
 * The second argument is optional. If not given, __LINE__ is implied, and as
 * such the macro will generate the same identifier if used multiple times on
 * the same code-line (or within a macro). This should be used if recursive
 * calls into the macro are not expected. In fact, no argument is necessary in
 * this case, as a mere `C_VAR` will evaluate to a valid variable name.
 *
 * This helper may be used by macro implementations that might reasonable well
 * be called in a stacked fasion, like:
 *
 *     c_max(foo, c_max(bar, baz))
 *
 * Such a stacked call of c_max() might cause compiler warnings of shadowed
 * variables in the definition of c_max(). By using C_VAR(), such warnings
 * can be silenced as each evaluation of c_max() uses unique variable names.
 *
 * Return: This evaluates to a constant identifier.
 */
#define C_VAR(...) C_INTERNAL_VAR(__VA_ARGS__, 2, 1)
#define C_INTERNAL_VAR(_x, _uniq, _num, ...) C_VAR ## _num (_x, _uniq)
#define C_VAR1(_x, _unused) C_VAR2(_x, C_CONCATENATE(line, __LINE__))
#define C_VAR2(_x, _uniq) C_CONCATENATE(c_internal_var_unique_, C_CONCATENATE(_uniq, _x))

/**
 * C_CC_MACRO1() - provide safe environment to a macro
 * @_call:      macro to call
 * @_x1:        first argument
 * @...:        further arguments to forward unmodified to @_call
 *
 * This function simplifies the implementation of macros. Whenever you
 * implement a macro, provide the internal macro name as @_call and its
 * argument as @_x1. Inside of your internal macro, you...
 *
 *  - ...are safe against multiple evaluation errors, since C_CC_MACRO1 will
 *       store the initial parameters in temporary variables.
 *
 *  - ...support constant folding, as C_CC_MACRO1 takes care to invoke your
 *       macro with the original values, if they are compile-time constant.
 *
 *  - ...have unique variable names for recursive callers and will not run into
 *       variable-shadowing-warnings accidentally.
 *
 *  - ...have properly typed arguments as C_CC_MACRO1 stores the original
 *       arguments in an `__auto_type` temporary variable.
 *
 * Return: Result of @_call is returned.
 */
#define C_CC_MACRO1(_call, _x1, ...) C_INTERNAL_CC_MACRO1(_call, __COUNTER__, (_x1), ## __VA_ARGS__)
#define C_INTERNAL_CC_MACRO1(_call, _x1q, _x1, ...)                     \
        __builtin_choose_expr(                                          \
                __builtin_constant_p(_x1),                              \
                _call(_x1, ## __VA_ARGS__),                             \
                __extension__ ({                                        \
                        const __auto_type C_VAR(X1, _x1q) = (_x1);      \
                        _call(C_VAR(X1, _x1q), ## __VA_ARGS__);         \
                }))

/**
 * C_CC_MACRO2() - provide safe environment to a macro
 * @_call:      macro to call
 * @_x1:        first argument
 * @_x2:        second argument
 * @...:        further arguments to forward unmodified to @_call
 *
 * This is the 2-argument equivalent of C_CC_MACRO1().
 *
 * Return: Result of @_call is returned.
 */
#define C_CC_MACRO2(_call, _x1, _x2, ...) C_INTERNAL_CC_MACRO2(_call, __COUNTER__, (_x1), __COUNTER__, (_x2), ## __VA_ARGS__)
#define C_INTERNAL_CC_MACRO2(_call, _x1q, _x1, _x2q, _x2, ...)                          \
        __builtin_choose_expr(                                                          \
                (__builtin_constant_p(_x1) && __builtin_constant_p(_x2)),               \
                _call((_x1), (_x2), ## __VA_ARGS__),                                    \
                __extension__ ({                                                        \
                        const __auto_type C_VAR(X1, _x1q) = (_x1);                      \
                        const __auto_type C_VAR(X2, _x2q) = (_x2);                      \
                        _call(C_VAR(X1, _x1q), C_VAR(X2, _x2q), ## __VA_ARGS__);        \
                }))

/**
 * C_CC_MACRO3() - provide safe environment to a macro
 * @_call:      macro to call
 * @_x1:        first argument
 * @_x2:        second argument
 * @_x3:        third argument
 * @...:        further arguments to forward unmodified to @_call
 *
 * This is the 3-argument equivalent of C_CC_MACRO1().
 *
 * Return: Result of @_call is returned.
 */
#define C_CC_MACRO3(_call, _x1, _x2, _x3, ...) C_INTERNAL_CC_MACRO3(_call, __COUNTER__, (_x1), __COUNTER__, (_x2), __COUNTER__, (_x3), ## __VA_ARGS__)
#define C_INTERNAL_CC_MACRO3(_call, _x1q, _x1, _x2q, _x2, _x3q, _x3, ...)                               \
        __builtin_choose_expr(                                                                          \
                (__builtin_constant_p(_x1) && __builtin_constant_p(_x2) && __builtin_constant_p(_x3)),  \
                _call((_x1), (_x2), (_x3), ## __VA_ARGS__),                                             \
                __extension__ ({                                                                        \
                        const __auto_type C_VAR(X1, _x1q) = (_x1);                                      \
                        const __auto_type C_VAR(X2, _x2q) = (_x2);                                      \
                        const __auto_type C_VAR(X3, _x3q) = (_x3);                                      \
                        _call(C_VAR(X1, _x1q), C_VAR(X2, _x2q), C_VAR(X3, _x3q), ## __VA_ARGS__);       \
                }))

/**
 * C_ARRAY_SIZE() - calculate number of array elements at compile time
 * @_x:         array to calculate size of
 *
 * Return: Evaluates to a constant integer expression.
 */
#define C_ARRAY_SIZE(_x)                                                \
        C_EXPR_ASSERT(sizeof(_x) / sizeof((_x)[0]),                     \
               /*                                                       \
                * Verify that `_x' is an array, not a pointer. Rely on  \
                * `&_x[0]' degrading arrays to pointers.                \
                */                                                      \
                !__builtin_types_compatible_p(                          \
                        __typeof__(_x),                                 \
                        __typeof__(&(*(__typeof__(_x)*)0)[0])           \
                ),                                                      \
                "C_ARRAY_SIZE() called with non-array argument"         \
        )

/**
 * C_DECIMAL_MAX() - calculate maximum length of the decimal
 *                   representation of an integer
 * @_type: integer variable/type
 *
 * This calculates the bytes required for the decimal representation of an
 * integer of the given type. It accounts for a possible +/- prefix, but it
 * does *NOT* include the trailing terminating zero byte.
 *
 * Return: Evaluates to a constant integer expression
 */
#define C_DECIMAL_MAX(_arg)                                                             \
        (_Generic((__typeof__(_arg)){ 0 },                                              \
                        char: C_INTERNAL_DECIMAL_MAX(sizeof(char)),                     \
                 signed char: C_INTERNAL_DECIMAL_MAX(sizeof(signed char)),              \
               unsigned char: C_INTERNAL_DECIMAL_MAX(sizeof(unsigned char)),            \
                signed short: C_INTERNAL_DECIMAL_MAX(sizeof(signed short)),             \
              unsigned short: C_INTERNAL_DECIMAL_MAX(sizeof(unsigned short)),           \
                  signed int: C_INTERNAL_DECIMAL_MAX(sizeof(signed int)),               \
                unsigned int: C_INTERNAL_DECIMAL_MAX(sizeof(unsigned int)),             \
                 signed long: C_INTERNAL_DECIMAL_MAX(sizeof(signed long)),              \
               unsigned long: C_INTERNAL_DECIMAL_MAX(sizeof(unsigned long)),            \
            signed long long: C_INTERNAL_DECIMAL_MAX(sizeof(signed long long)),         \
          unsigned long long: C_INTERNAL_DECIMAL_MAX(sizeof(unsigned long long))))
#define C_INTERNAL_DECIMAL_MAX(_bytes)                                          \
        C_EXPR_ASSERT(                                                          \
                1 + ((_bytes) <= 1 ?  3 :                                       \
                     (_bytes) <= 2 ?  5 :                                       \
                     (_bytes) <= 4 ? 10 :                                       \
                                     20),                                       \
                (_bytes) <= 8,                                                  \
                "Invalid use of C_INTERNAL_DECIMAL_MAX()"                       \
        )

/**
 * c_container_of() - cast a member of a structure out to the containing structure
 * @_ptr:       pointer to the member or NULL
 * @_type:      type of the container struct this is embedded in
 * @_member:    name of the member within the struct
 *
 * This uses `offsetof(3)` to turn a pointer to a structure-member into a
 * pointer to the surrounding structure.
 *
 * Return: Pointer to the surrounding object.
 */
#define c_container_of(_ptr, _type, _member) C_CC_MACRO1(C_CONTAINER_OF, (_ptr), _type, _member)
#define C_CONTAINER_OF(_ptr, _type, _member)                                            \
        __extension__ ({                                                                \
                /* trigger warning if types do not match */                             \
                (void)(&((_type *)0)->_member == (_ptr));                               \
                _ptr ? (_type*)( (char*)_ptr - offsetof(_type, _member) ) : NULL;       \
        })

/**
 * c_max() - compute maximum of two values
 * @_a:         value A
 * @_b:         value B
 *
 * Calculate the maximum of both passed values. Both arguments are evaluated
 * exactly once, under all circumstances. Furthermore, if both values are
 * constant expressions, the result will be constant as well.
 *
 * The comparison of their values is performed with the types given by the
 * caller. It is the caller's responsibility to convert them to suitable types
 * if necessary.
 *
 * Return: Maximum of both values is returned.
 */
#define c_max(_a, _b) C_CC_MACRO2(C_MAX, (_a), (_b))
#define C_MAX(_a, _b) ((_a) > (_b) ? (_a) : (_b))

/**
 * c_min() - compute minimum of two values
 * @_a:         value A
 * @_b:         value B
 *
 * Calculate the minimum of both passed values. Both arguments are evaluated
 * exactly once, under all circumstances. Furthermore, if both values are
 * constant expressions, the result will be constant as well.
 *
 * The comparison of their values is performed with the types given by the
 * caller. It is the caller's responsibility to convert them to suitable types
 * if necessary.
 *
 * Return: Minimum of both values is returned.
 */
#define c_min(_a, _b) C_CC_MACRO2(C_MIN, (_a), (_b))
#define C_MIN(_a, _b) ((_a) < (_b) ? (_a) : (_b))

/**
 * c_less_by() - calculate clamped difference of two values
 * @_a:         minuend
 * @_b:         subtrahend
 *
 * Calculate [_a - _b], but clamp the result to 0. Both arguments are evaluated
 * exactly once, under all circumstances. Furthermore, if both values are
 * constant expressions, the result will be constant as well.
 *
 * The comparison of their values is performed with the types given by the
 * caller. It is the caller's responsibility to convert them to suitable types
 * if necessary.
 *
 * Return: This computes [_a - _b], if [_a > _b]. Otherwise, 0 is returned.
 */
#define c_less_by(_a, _b) C_CC_MACRO2(C_LESS_BY, (_a), (_b))
#define C_LESS_BY(_a, _b) ((_a) > (_b) ? (_a) - (_b) : 0)

/**
 * c_clamp() - clamp value to lower and upper boundary
 * @_x:         value to clamp
 * @_low:       lower boundary
 * @_high:      higher boundary
 *
 * This clamps @_x to the lower and higher bounds given as @_low and @_high.
 * All arguments are evaluated exactly once, and yield a constant expression if
 * all arguments are constant as well.
 *
 * The comparison of their values is performed with the types given by the
 * caller. It is the caller's responsibility to convert them to suitable types
 * if necessary.
 *
 * Return: Clamped integer value.
 */
#define c_clamp(_x, _low, _high) C_CC_MACRO3(C_CLAMP, (_x), (_low), (_high))
#define C_CLAMP(_x, _low, _high) ((_x) > (_high) ? (_high) : (_x) < (_low) ? (_low) : (_x))

/**
 * c_div_round_up() - calculate integer quotient but round up
 * @_x:         dividend
 * @_y:         divisor
 *
 * Calculates [x / y] but rounds up the result to the next integer. All
 * arguments are evaluated exactly once, and yield a constant expression if all
 * arguments are constant.
 *
 * Note:
 * [(x + y - 1) / y] suffers from an integer overflow, even though the
 * computation should be possible in the given type. Therefore, we use
 * [x / y + !!(x % y)]. Note that on most CPUs a division returns both the
 * quotient and the remainder, so both should be equally fast. Furthermore, if
 * the divisor is a power of two, the compiler will optimize it, anyway.
 *
 * The operationsare performed with the types given by the caller. It is the
 * caller's responsibility to convert the arguments to suitable types if
 * necessary.
 *
 * Return: The quotient is returned.
 */
#define c_div_round_up(_x, _y) C_CC_MACRO2(C_DIV_ROUND_UP, (_x), (_y))
#define C_DIV_ROUND_UP(_x, _y) ((_x) / (_y) + !!((_x) % (_y)))

/**
 * c_align_to() - align value to a multiple
 * @_val:       value to align
 * @_to:        align to multiple of this
 *
 * This aligns @_val to a multiple of @_to. If @_val is already a multiple of
 * @_to, @_val is returned unchanged. This function operates within the
 * boundaries of the type of @_val and @_to. Make sure to cast them if needed.
 *
 * The arguments of this macro are evaluated exactly once. If both arguments
 * are a constant expression, this also yields a constant return value.
 *
 * Note that @_to must be a power of 2, otherwise the behavior will not match
 * expectations.
 *
 * Return: @_val aligned to a multiple of @_to
 */
#define c_align_to(_val, _to) C_CC_MACRO2(C_ALIGN_TO, (_val), (_to))
#define C_ALIGN_TO(_val, _to) (((_val) + (_to) - 1) & ~((_to) - 1))

/**
 * c_assert() - runtime assertions
 * @expr_result:                result of an expression
 *
 * This function behaves like the standard `assert(3)` macro. That is, if
 * `NDEBUG` is defined, it is a no-op. In all other cases it will assert that
 * the result of the passed expression is true.
 *
 * Unlike the standard `assert(3)` macro, this function always evaluates its
 * argument. This means side-effects will always be evaluated! However, if the
 * macro is used with constant expressions, the compiler will be able to
 * optimize it away.
 */
#define c_assert(_x) ({                                                         \
                const _c_unused_ bool c_assert_result = (_x);                   \
                assert(c_assert_result && #_x);                                 \
        })

/**
 * c_errno() - return valid errno
 *
 * This helper should be used to shut up gcc if you know 'errno' is valid (ie.,
 * errno is > 0). Instead of "return -errno;", use
 * "return -c_errno();" It will suppress bogus gcc warnings in case it assumes
 * 'errno' might be 0 (or <0) and thus the caller's error-handling might not be
 * triggered.
 *
 * This helper should be avoided whenever possible. However, occasionally we
 * really want to shut up gcc (especially with static/inline functions). In
 * those cases, gcc usually cannot deduce that some error paths are guaranteed
 * to be taken. Hence, making the return value explicit allows gcc to better
 * optimize the code.
 *
 * Note that you really should never use this helper to work around broken libc
 * calls or syscalls, not setting 'errno' correctly.
 *
 * Return: Positive error code is returned.
 */
static inline int c_errno(void) {
        return _c_likely_(errno > 0) ? errno : ENOTRECOVERABLE;
}

/*
 * Common Destructors
 *
 * Followingly, there're a bunch of common 'static inline' destructors, which
 * simply call the function that they're named after, but return "INVALID"
 * instead of "void". This allows direct assignment to any member-field and/or
 * variable they're defined in, like:
 *
 *   foo = c_free(foo);
 *
 * or
 *
 *   foo->bar = c_close(foo->bar);
 *
 * Furthermore, all those destructors can be safely called with the "INVALID"
 * value as argument, and they will be a no-op.
 */

static inline void *c_free(void *p) {
        free(p);
        return NULL;
}

static inline int c_close(int fd) {
        if (fd >= 0)
                close(fd);
        return -1;
}

static inline FILE *c_fclose(FILE *f) {
        if (f)
                fclose(f);
        return NULL;
}

static inline DIR *c_closedir(DIR *d) {
        if (d)
                closedir(d);
        return NULL;
}

/*
 * Common Cleanup Helpers
 *
 * A bunch of _c_cleanup_(foobarp) helpers that are used all over the place.
 * Note that all of those have the "if (IS_INVALID(foobar))" check inline, so
 * compilers can optimize most of the cleanup-paths in a function. However, if
 * the function they call already does this _inline_, then it might be skipped.
 */

#define C_DEFINE_CLEANUP(_type, _func)                                          \
        static inline void _func ## p(_type *p) {                               \
                if (*p)                                                         \
                        _func(*p);                                              \
        } struct c_internal_trailing_semicolon

#define C_DEFINE_DIRECT_CLEANUP(_type, _func)                                   \
        static inline void _func ## p(_type *p) {                               \
                _func(*p);                                                      \
        } struct c_internal_trailing_semicolon

static inline void c_freep(void *p) {
        /*
         * `foobar **` does not coerce to `void **`, so we need `void *` as
         * argument type, and then we dereference manually.
         */
        c_free(*(void **)p);
}

C_DEFINE_DIRECT_CLEANUP(int, c_close);
C_DEFINE_CLEANUP(FILE *, c_fclose);
C_DEFINE_CLEANUP(DIR *, c_closedir);

#ifdef __cplusplus
}
#endif