cstdlib 770 Bytes
#pragma once

#include <stdlib.h>

#if __cplusplus >= 201703L
extern int abs (int __x) throw()  __attribute__ ((__const__)) ;
extern long int labs (long int __x) throw() __attribute__ ((__const__)) ;
extern float fabs (float __x) throw() __attribute__ ((__const__)) ;
#else
extern int abs (int __x) __attribute__ ((__const__)) ;
extern long int labs (long int __x) __attribute__ ((__const__)) ;
extern float fabs (float __x) __attribute__ ((__const__)) ;
#endif

namespace std
{

using ::abs;

inline long
abs(long __i) { return __builtin_labs(__i); }

inline long long
abs(long long __x) { return __builtin_llabs (__x); }

float fabs(float __x) { return __builtin_fabs(__x); }

float abs(float __x) { return fabs(__x); }
double abs(double __x) { return fabs(__x); }

}