C++ converting HELP: hex to decimal but using a 64bit 16byte hex

nellyrev · 12-04-2007 07:22PM #1

If this is the wrong place for this then sorry

ok here is the problem

i get an input from the user in hex format and of 16hex values ie 8bytes long(64bits) and is stored in the following:

char hex[16];

and then i am using the following to convert it to decimal

sscanf( hex, "%X", &hexInt );
itoa(hexInt,binChar,2);

where

uint64_t hexInt;
char binChar[64];

now this seems to work but i am only getting an 8bit output and i do not think its is even the right output

any help ?

Webmonkey · 12-04-2007 07:58PM

Shouldn't itoa(hexInt,binChar,2); be itoa(hexInt,binChar,16); ?

nellyrev · 12-04-2007 08:15PM

oh god no

im converting hex to dec not hex to hex

EDIT sorry

sscanf( hex, "%X", &hexInt ); // Hex To Dec
itoa(hexInt,binChar,2); // Dec To Bin

man my hungarian notation is bad

it should be this

sscanf( hex, "%X", &decInt );
itoa(decInt,binChar,2);

Webmonkey · 12-04-2007 08:17PM

God i'm all confused.

Why you using itoa (Integer to Ascii) when it is Hex to double you want to do? The 2 in the itoa is for binary.

10 is for double so it would be

itoa(hexInt,binChar,10)

Am i totally mis understanding you here?

Webmonkey · 12-04-2007 08:30PM

This works

int hex;
	char binChar[80];
	
	scanf("%x",&hex);
	itoa(hex,binChar,10);
	printf("%s",binChar);

Not sure if this what you want - you have me all confused!

This Reads in Hex as ASCII.
Converts ASCII (as hex value) to Double.
Prints out this double

nellyrev · 12-04-2007 09:12PM

say the input is:

0123456789abcdef // variable hex

then sscanf( hex, "%X", &hexInt ); // converts to decimal

where hexInt has the value 2309737967

but it should be 81985529216486895

is sscanf the wrong command to do it with ?

Webmonkey · 12-04-2007 09:18PM

Oh yes i see, for large numbers a problem occurs. Take it that the int just a 32bit one so it can only accomodate so much. I amn't sure to be honest :S

nellyrev · 12-04-2007 09:21PM

thank you for trying

EDIT i would show you more code but its top secret , but not really

DublinDilbert · 12-04-2007 10:14PM

If your writting in C++ you can just use Cin as follows:-

long64 input_data;
cout << "Please enter 16 hex characters";
cin >> hex >> input_data;

nellyrev · 13-04-2007 12:39AM

mmm the compile does not recognise long64

Martyr · 13-04-2007 05:27AM

you don't say what compiler you use or if in c/c++
i did this c code here, but the result is off by 1 byte..so its unreliable, probably c lib routine does it all anyway, i don't know.

[PHP]#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main(int argc, char *argv[])
{
double bignumber=0.0;
int i,length;
char number;

while(--argc) {

length = strlen(argv[1]);

for(i=0;i<length;i++) {

number = argv[1];

if(number >= 'a')
number -= 'a' - 10;
else
number -= '0';

bignumber *= 16;
bignumber += number;
}
printf("\n%0.f",bignumber);
}
}[/PHP]

example:
test 0123456789abcdef

output:
81985529216486896

but in calculator, it gives 81985529216486895 hehe

EDIT:i noticed that while the bignumber is the same output as calc.exe on windows, printf gives bignumber + 1

Correction:i don't know why it 1 is added, but maybe its my computer.
81985529216486895 is in fpu before move to bignumber variable, but when move to stack for printf, it then has 1+ more.

EDIT: the 1+ added, i found out, is because the use of double, i was told that __int64 and _atoi64() for GCC (what i'm using) would work, although, it will depend on compiler too..

nellyrev · 13-04-2007 12:32PM

I am using C++ and Borland's C++ builder 6

Webmonkey · 13-04-2007 12:42PM

No problem, but you seem to be using very C style code, you coming from C background?

joe_chicken · 13-04-2007 12:43PM

nellyrev wrote:

16bytes long(64bits)

emmm... this might be a stupid question (please don't be too harsh)

But does 16bytes not equal 128 bits?

Webmonkey · 13-04-2007 12:45PM

joe_chicken wrote:

emmm... this might be a stupid question (please don't be too harsh)

But does 16bytes not equal 128 bits?

You are right. It is 8 bytes that is 64bit.

joe_chicken · 13-04-2007 01:20PM

Just a quick compile on Dev-cpp (gcc) and I see that itoa doesn't give any compile errors, but is only converting 32 bits of the 64 bits

Doing a little googling and there's an i64toa function, but I don't seem to have any library for that.

Martyr · 13-04-2007 01:34PM

emmm... this might be a stupid question (please don't be too harsh)

But does 16bytes not equal 128 bits?

yeah, the string is 128-bits, but the actual value can be stored in 64-bits

nellyrev, the code i wrote, if you change the format %0.f to %i64d and change double to int64 (try prefixing _) then it should work, i know it works in MSVC, but as before, probably easier way, like with atoi64

the reason the double adds 1 more, is because the FPU is inprecise when storing the value from the stack into variable, you won't have this problem if using int64

joe_chicken · 13-04-2007 01:58PM

Average Joe wrote:

yeah, the string is 128-bits, but the actual value can be stored in 64-bits

ahhh, I see... thanks

nellyrev · 13-04-2007 04:53PM

doh on the 16byte thing

i guess i meant 16 hex values

anyway i got an update

i just separated the hex into 2 which is kinda what i have to do anyway

but still the sscanf is not giving me what i need

here is the code :

uint64_t hexkeyIntL = 0;
        // sets the left side of the key
        for(i=0; i<8; i++)
        hexkeyL[i] = hexkey16[i];

        // input hexkey16 is 0123456701234567 where hexkeyL is 01234567 & where hexkeyR is 01234567
   *     sscanf( hexkeyL, "%x", &deckeyIntL ); // gives the right result where 19088743
        _i64toa(hexkeyIntL,binkeyCharL,2);
        printf("%s",binkeyCharL);
        //sets the right side of the key
        i=0;
        uint64_t hexkeyIntR = 0;
        for(j=8;j<16;j++){
        hexkeyR[i] = hexkey16[j];
        i++;
        }

    *    sscanf( hexkeyR, "%x", &hexkeyIntR ); // doesnt give the right result 4294967295 meaning sscanf thinks hexkeyR is 0xFFFFFFFF
        _i64toa(hexkeyIntR,binkeyCharR,2);
        printf("%s\n",binkeyCharR);

so any answers to the lines marked with *

is there a way to convert the hex to dec or even convert the hex to bin instantly

nellyrev · 13-04-2007 05:04PM

Webmonkey wrote:

No problem, but you seem to be using very C style code, you coming from C background?

last year in college we used C i dont really know how to do the conversion with C++.

also Webmonkey your code is weird(over my head) to me lol

Martyr · 13-04-2007 06:26PM

using DublinDilbert's suggestion

[PHP]
#include <iostream>

using namespace std;

void toBin64(__int64 number);

int main(int argc,char *argv[])
{
__int64 input_data;

cout << "Please enter 16 hex characters:";
cin >> hex >> input_data;

cout << "\n\nDecimal:" << dec << input_data << endl;
cout << "Hexadecimal:" << hex << input_data << endl;
cout << "Binary:";
tobin64(input_data);

return 0;
}

void toBin64(__int64 number)
{
for(int i=63;i>=0;i--)
cout << ((number >> i) & 1);
}[/PHP]

Please enter 16 hex characters:0123456789abcdef


Decimal:81985529216486895
Hexadecimal:123456789abcdef
Binary:0000000100100011010001010110011110001001101010111100110111101111

nellyrev · 13-04-2007 08:12PM

that is very cool and i have seen most of the above but how can i need to be able to store these conversions

not just display them

C++ converting HELP: hex to decimal but using a 64bit 16byte hex

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