Question

I have this code in Java:

   String pr = "4173df24c969ff63"
   long prLongBits = Long.valueOf(pr, HEX_BASE).longValue();
   prDoubleValue = Double.longBitsToDouble(prLongBits);

the result of: prDoubleValue = 2.083694058837832E7

How would i convert this in Objective C??
i tried to convert from hex to long and then long to double, but no proper result.

BR,

Suppi

Answer 1

I would try something like the following:

// Read the hex string into a 64-bit integer
unsigned long long doubleBits;
double result;
NSScanner *scanner = [NSScanner scannerWithString:@"4173df24c969ff63"];
if ([scanner scanHexLongLong:&doubleBits]) {
    memcpy(&result, &doubleBits, sizeof(result)l
}

I haven’t tried it out but the basic idea should be approximately right. You want to convert the hex string to a bunch of bytes stored in a numeric data type of an appropriate size. Once that bit pattern is in memory we copy it into the memory assigned to a double.

This assumes that the string representation used to create the hex string used the same byte ordering as the one where your code is running.