Hi,
I'm writing classes for basic types, so that code is logicly the same on multiple platforms and compilators (like int_least16_t for int). For fun! (I'm still a student)
And I read this:
And what's worse:
Floating-point types MAY support special values: ∞, NaN or -0
Which means that float MAY be unsigned...
I know it's like with __int128, and standard is just a standard,
but still...
IEEE-754 is from 1985, but same machines can be weird,
and same legacy hardware doesn't have a floating unit.
As I understand, float is mendatory (not optional like int16_t), but can be in any standart, and any set of values can be posible?
Only thing we heve are same macros(<cfloat>):
FLT_MIN,FLT_MAX- Even ifFLT_MIN = IEEE-754::FLT_MIN, float can be non IEEE-754. For egzample float with: fliped exponent with fraction...FLT_RADIX- Base system? If so, can help to write the exact value. But still float can be 3 bit or 200 bit (in size)...FLT_EPSILON- (from 1 to next) We might use it (with base) to check fraction size...FLT_MANT_DIG- Is it "mantisa" digits / fraction size?FLT_MAX_EXP- Exponent filled with 1... in IEEE-754, but outside can be a random number?
If float is like IEEE-754 (sign,exponent,fraction), then it's easy, but if -0 and NaN are optional then it MAY be difrent. Because I can't tell them apart, I can't use bit representation (in safe manner). And if ∞ is optional float is no longer safe type.
The only way out I see is to add makro to compiler.
I know it's theoretical problem, but I'm intrested if there is any check posible or We all write implementation dependend code, when We use float keyword?
CodePudding user response：
In C , the value of std::numeric_limits<T>::is_iec559 shall be true for all floating-point types T "if, and only if, the type adheres to ISO/IEC/IEEE 60559" and ISO/IEC/IEEE 60559:2011 is the same as IEEE 754-2008, so:
#include <iostream>
#include <limits>
int main() {
std::cout << std::boolalpha << std::numeric_limits<float>::is_iec559 << '\n';
}
Note: As noted in the comments, some implementations may still report true for this constant event though their floating point types are not following the IEEE 754-2008 standard to the letter.
For example, in gcc, you can compile with the options -Ofast or -ffast-math which in turn sets a number of options which can result in incorrect output for programs that depend on an exact implementation of IEEE or ISO rules/specifications for math functions.