How can I convert longbits to double in objective-C?

Question

In java I can use Double.longBitsToDouble() static function but in objective-C I can't find a way to do like that. How can I get that?

Thanks :)

Answer 1

I didn't really use that method in Java much, but what is wrong with simply setting a long long value to a variable of type double?

A long long will be 64 bits regardless of platform.

You can check for NaN in the double using isnan() in math.h if needed.

Answer 2

You can use memcpy to copy the bit representation into the address of a variable of type double. I'm not sure whether this enters the realm of undefined behaviour.

//assert(sizeof(double) == sizeof(unsigned long long));

unsigned long long bitPattern = 0x7ff0000000000000ULL;
double doubleValue;

memcpy(&doubleValue, &bitPattern, sizeof doubleValue);

//assert(isinf(doubleValue));

The bit pattern for positive infinity was borrowed from this page which appears to document the longBitsToDouble method.

Answer 3

uint64_t bitPattern = whatever;// use this rather than long long because it is explicitly 64 bits
double  doubleValue;
doubleValue = *(double*)&bitPattern;