hexadecimal to double

drauk · 04-05-2010, 12:22 PM

Hi all
Someone know how i can convert from hex string to double in c/c++??

Example 40668472B020C49C is 180.139

reference page:
http://babbage.cs.qc.edu/IEEE-754/64bit.html

Thanks.

Sergei Steshenko · 04-05-2010, 12:33 PM

Quote:

Originally Posted by drauk

Hi all
Someone know how i can convert from hex string to double in c/c++??

Example 40668472B020C49C is 180.139

reference page:
http://babbage.cs.qc.edu/IEEE-754/64bit.html

Thanks.

Start looking for answers here: http://en.wikipedia.org/wiki/Floating_point .

David1357 · 04-05-2010, 01:33 PM

Quote:

Originally Posted by drauk

Someone know how i can convert from hex string to double in c/c++??

Code:

    // Allocate a double on the stack
    double result;
    // Allocate a byte pointer on the stack
    unsigned char *byte;
    // Allocate a byte array on the stack
    unsigned char array[8];

    // Get the address of the double
    byte = &result;

    // Convert the string to bytes and save the values in the array
    for (int i = 0; i < 8; i++)
    {
        // Your solution here
    }

    // Copy the byte array to the byte pointer
    memcpy(byte, array, 8);

    // Print out your double
    printf("%f\n", result);

smeezekitty · 04-05-2010, 01:58 PM

Code:

double *d;
uint_64_t p = 0x40668472B020C49C;
d = (double *)&p;

Sergei Steshenko · 04-05-2010, 02:02 PM

Quote:

Originally Posted by smeezekitty

Code:

double *d;
uint_64_t p = 0x40668472B020C49C;
d = (double *)&p;

Endianness ?

smeezekitty · 04-05-2010, 02:10 PM

I thought it was little endian.

Sergei Steshenko · 04-05-2010, 02:34 PM

Quote:

Originally Posted by smeezekitty

I thought it was little endian.

80 bits or 64 bits (the OP wants 64 bits, but how will your conversion work ?) ?

David1357 · 04-06-2010, 09:59 AM

Quote:

Originally Posted by smeezekitty

Code:

uint_64_t p = 0x40668472B020C49C;

What is really busted about this is that the OP wanted to handle strings.

Sergei Steshenko · 04-06-2010, 10:38 AM

Quote:

Originally Posted by David1357

What is really busted about this is that the OP wanted to handle strings.

The string issue can be dealt with by 'atol' and friends. But the point is to understand FP number internal structure - I guess.

David1357 · 04-07-2010, 08:47 AM

Quote:

Originally Posted by Sergei Steshenko

The string issue can be dealt with by 'atol' and friends.

You know what? I had a major brain fade and forgot about strtoull!

Oh well, it looks a lot like a homework problem, and I didn't want to give too much help. Looks like I exceeded my goal.

drauk · 04-07-2010, 11:43 AM

Thanks all for your help, is not a homework i'm trying to read/understand the FLV header, and almost all the metadata values are double