Safe bounded casting between types.

EvilCast.h

#if __has_extension(c_generic_selections) && __has_extension(c_static_assert)
    #import "EvilCastImpl.h"
    // Returns the value of s, clamping it to the bounds of type t. s and d must either both be integers
    // or both be floating-point values.
    #define EvilBoundedCheckedCast(t, s) __EvilChecked(t, s, Cast)
    
    // Tries to assign the value of s to d, returning 1 if s is within the bounds of s and 0 if not.
    // s and d must either both be integers or both be floating-point values.
    #define EvilCheckedAssign(d, s) __EvilChecked(d, s, Assign)
#else
    #error Compiler features necessary for implementing EvilBoundedCheckedCast and EvilCheckedCast are not present.
#endif

EvilCastImpl.h

#define __EvilMinOfCastableType(T) _Generic(T, \
    char: CHAR_MIN, \
    unsigned char: 0, \
    short: SHRT_MIN, \
    unsigned short: 0, \
    int: INT_MIN, \
    unsigned int: 0, \
    long: LONG_MIN, \
    unsigned long: 0, \
    float: -FLT_MAX, \
    double: -DBL_MAX \
)
#define __EvilMaxOfCastableType(T) _Generic(T, \
    char: CHAR_MAX, \
    unsigned char: UCHAR_MAX, \
    short: SHRT_MAX, \
    unsigned short: USHRT_MAX, \
    int: INT_MAX, \
    unsigned int: UINT_MAX, \
    long: LONG_MAX, \
    unsigned long: ULONG_MAX, \
    float: FLT_MAX, \
    double: DBL_MAX \
)
#define __EvilIsCastableFloatType(T) _Generic(T, \
    float: 1, \
    double: 1, \
    const float: 1, \
    const double: 1, \
    default: 0 \
)

#define __EvilIsCastableIntType(T) _Generic(T, \
    char: 1, \
    unsigned char: 1, \
    short: 1, \
    unsigned short: 1, \
    int: 1, \
    unsigned int: 1, \
    long: 1, \
    unsigned long: 1, \
    const char: 1, \
    const unsigned char: 1, \
    const short: 1, \
    const unsigned short: 1, \
    const int: 1, \
    const unsigned int: 1, \
    const long: 1, \
    const unsigned long: 1, \
    default: 0 \
)

#define __EvilCheckedAssignWithBoundType(d, s, bt) \
  ((__builtin_expect((bt)s > (bt)__EvilMaxOfCastableType(d) || (bt)s < (bt)__EvilMinOfCastableType(d), 0)) \
   ? ({NSCAssert(NO, @"Out-of-bounds type assignment failed"); 0;}) \
   : ({d = (__typeof(d))s; 1;}) \
  )

#define __EvilCheckedCastWithBoundType(t, s, bt) \
  ({t __tt; \
   __builtin_expect((bt)s > (bt)__EvilMaxOfCastableType(__tt), 0) \
   ? ({NSCAssert(NO, @"Out-of-bounds type assignment was clamped to max"); (t)__EvilMaxOfCastableType(__tt);}) \
   : ( \
      __builtin_expect((bt)s < (bt)__EvilMinOfCastableType(__tt), 0) \
      ? ({NSCAssert(NO, @"Out-of-bounds type assignment was clamped to min"); (t)__EvilMinOfCastableType(__tt);}) \
      : ({(t)s;}) \
     ); \
  })

#define __EvilCheckedIntAssign(d, s) __EvilCheckedAssignWithBoundType(d, s, long long)
#define __EvilCheckedFloatAssign(d, s) __EvilCheckedAssignWithBoundType(d, s, long double)
#define __EvilCheckedIntCast(t, s) __EvilCheckedCastWithBoundType(t, s, long long)
#define __EvilCheckedFloatCast(t, s) __EvilCheckedCastWithBoundType(t, s, long double)

#define __EvilChecked(a, b, s) \
({__typeof(a) __t; __typeof(b) __u = b; _Static_assert((__EvilIsCastableIntType(__t) && __EvilIsCastableIntType(__u)) \
                                   || (__EvilIsCastableFloatType(__t) && __EvilIsCastableFloatType(__u)), "Invalid types for EvilChecked" #s "."); \
  __EvilIsCastableIntType(__t) && __EvilIsCastableIntType(__u) \
  ? __EvilCheckedInt##s(a, __u) \
  : (__EvilIsCastableFloatType(__t) && __EvilIsCastableFloatType(__u) \
     ? __EvilCheckedFloat##s(a, __u) \
     : (__typeof(a))({__builtin_unreachable(); 0;}) \
    ); \
})