C/C++ :: How To Locate The Lowest 8 Bits In A 64 Bit Key
Jul 15, 2014
I am trying to encrypt a plaintext using DES in C. I read about the algorithm and how it works, but when i came to write the code i struggled. :
How to locate the lowest 8-bits in a 64-bit key ?
How to shuffle the plaintext according to the algorithm description ? (I read about bitwise operations, but i still cannot understand how i can use them to transfer for example the 5th bit to the location of the 30th bit)
Left shifting the key would not wrap the bits, so i just bitwise or with a mask that will add the bits that did not wrap around?
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Nov 28, 2014
Write a program that has an array of at least 20 integers. It should call a function that uses the linear search algorithm to locate one of the values. The function should keep a count of the number of comparisons it makes until it finds the value. The program then should call a function that uses the binary search algorithm to locate the same value. It should also keep count of the number of comparisons it makes. Display these values on the screen.
/*
search benchmark.cpp
this program searchs through a array of 20 integers
*/
#include <iostream>
#include <string>
#include <iomanip>
using namespace std;
int array [20];
int count;
[Code] .....
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Jul 7, 2014
I need some basic code (not for an assignment) to write an add, delete and locate an node via the singly linked list.
I've looked at: [URL] .....
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May 14, 2013
I am working on a project where I need to retrive a double number and store 8 bits of the number in one field and the other 16 bits in another field. the code below gives me an error.
lata= lat>>8;
latb = (lat & 0xff);
The error states that & and >> are illegal for double. With this in mind, can I use these on a double. If not what can I do to achieve what I am trying to do?
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Feb 12, 2014
I am having a problem assigning bits a value of 0. The data is a 16 bit integer the bits greater than the 12th bit have garbage either a 0 or a 1. I would like to assign all bits greater than 12th bit the value 0 no matter what their values are. Whats the best approach.
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Aug 13, 2013
Using the old fashioned (unsigned) multiplication instruction in x64 assembly multiplies RAX (64 bit register) by a 64 bit register. The answer is stored in RDX:RAX (i.e. the answer is 128 bits). Is there any way, using native c++ to get the value in RDX (higher 64 bits)? One I can think of is: right/(limit/left) e.g. if we are limited to a byte then 97*123 would overflow:
97/(255/123) = 46 times, which is RDX's (if it was one byte) value. But this is too inefficient. Is there a fast way?
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Mar 25, 2014
Value x is a 32-bit unsigned integer 3:
00000000000000000000000000000011
If we use bitwise-shift to shift all bits to the right by 2, x is 0:
00000000000000000000000000000000
If we then do a bitwise leftshift on x by 30, do we end up with:
11000000000000000000000000000000
or
00000000000000000000000000000000
In other words, when we perform right shift which clips away the least most significant bits, and then do a left shift, is it possible for those bits to reappear?
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Apr 25, 2013
I am trying to retrieve the first three bits of a number. The code that I am using should work but it isn't giving me the correct result when trying certain numbers. Below is the code I am using:
unsigned short num1, num2 = 0;
unsigned short num = 65535// binary 111111111111111
num1 = num && 0x07;// gives me 1 but should give 7(111)
num2 = num >>3;//gives me 8191, which is correct
Why I am not getting the first three correct bits(111)?
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Sep 3, 2013
I am working on a project where I need to reverse bits for a number.
For example, if I have 110111100000000 I need to reverse it to 0000000001111011.
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Aug 8, 2013
I have a double variable and depending on certain conditions I need to set certain bits of an unsigned short Variable. For example, if double var is odd I need to set the 15th bit of the unsigned short variable.
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Mar 30, 2014
I'm trying to write a program that writes data to a disk in C++ without caring about it's file system. Here is what I can do so far:
#include <iostream>
#include <unistd.h>
#include <fcntl.h>
using namespace std;
char buffer[] = "Wow! I'm writing this data to a disk without puttting it into a file!";
int main(){
int Disk=open("/dev/sdb",O_RDWR);
write(Disk,buffer,sizeof(buffer));
close(Disk);
return 0;}
But this program can only write ASCII characters to the disk. But what if I want to mainipulate bits on the disk, how would I do that?
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Oct 10, 2014
I'm working on an assignment where I have to read an image in the PPM format. This format consists of a header that contains the parameters and the rest is raw bits.
I have to work with a modified PPM image that contains a secret message. This message is stored in the first X number of bytes. To decode a single character I would have to look at the lowest level bit of 8 bytes and return that as a character, then repeat this for the length of the message.
The code below is what I have so far, but I do not get the expected output but instead I get smiley-faces.... or other ASCII characters depending on the shift.
char buffer = 0;
int MsgSize =(size*8);
int nRead = 0;
printf("The secret message is displayed below: ");
for(i; i<MsgSize; i++) {
[Code] ....
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Jan 15, 2014
I just have a short question! I have an sbyte and I want to convert it to an int, but I do not want a value conversion, just to copy the bits, such that the negative numbers in the sbyte will be their complement in the int (-12 in sbyte -> 244 in int)... How can I do that?las
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Jun 24, 2013
I have a 64-bit uint64_t number:
Code:
Primitive<uint64_t> b = 0xCCCCCCCC00000000; I need to save the first 31 (most important) bits - 7FFFFFFE.
I found this solution in the Internet:
Code:
start = (((b)>>(first)) & ((1<<(((last+1)-(first))))-1)); but in my case for this code:
Code: Primitive<uint64_t> start = (((b)>>(32)) & ((1<<(((63+1)-(32))))-1));
I get an error: left shift count >= width of type
And even if I change 63 to 62:
Code:
Primitive<uint64_t> start = (((b)>>(32)) & ((1<<(((62+1)-(32))))-1));
I get: error: integer overflow in expression
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Sep 9, 2014
I was trying to program an decimal to binary converter (8-bits) in C. I am a complete beginner so I tried to put the 1's and 0's of the binary number as they come without reversing the order for beginning. I have seen example on the internet but didn't understand them so I decided to write it as I understood it. So, I typed the code as shown below:
Code:
#include <stdio.h>
#include <stdlib.h>
int main() {
int number;
int BitNum[8], x;
[Code] ....
The problem with the code is that if binary form has 0s in it then program displays a random number instead of a 0. For example if decimal is 7, it should print out 11100000 but it displays only 111(and some stupid numbers instead of 0). I have tried to solve it but failed.
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Oct 3, 2013
So I'm supposed to write a code that asks a user for a string and then displays the hex, decimal, and binary code for each individual letter and then tells the user how many bits in binary were 1. For example: Enter a line of text: Hello
The ASCII code for 'H' is 0x48 in hex, 72 in decimal, or 01001000 in binary, 2 bits were set.
The ASCII code for 'e' is 0x65 in hex, 101 in decimal, or 01100101 in binary, 4 bits were set.
The ASCII code for 'l' is 0x6c in hex, 108 in decimal, or 01101100 in binary, 4 bits were set.
The ASCII code for 'l' is 0x6c in hex, 108 in decimal, or 01101100 in binary, 4 bits were set.
The ASCII code for 'o' is 0x6f in hex, 111 in decimal, or 01101111 in binary, 6 bits were set.
So far I've got a code that will display the binary bit pattern by shifting a mask and testing for a 1 or 0. The problem is I can't figure out how to make it so the 1's and 0's get put into a single integer rather than just printing out. I hope that makes sense. Here's my whole code.
Code:
#include<stdio.h>
main ()
{
int i;
char input;
printf ("Enter ........: ");
scanf ("%c", &input);
for (i = 1; i <= 8; i++)
[Code]...
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Jan 3, 2015
The task is to return the number of bits set to true.Here is my code:
Code:
int cardinalityBS(PBitSet _this) {
int s, counter = 0;
for(s = 0; s < 31; s++) {
counter += _this->bits & 1;
_this->bits <<= 1;
}
return counter;
}
[code]....
The code is not working, since whenever I set _this->bits to a number, it returns me the wrong result.
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May 13, 2013
I made this program to convert bits to bytes, because I'm so sick of seeing ISP's advertise speeds in megabits, which I consider an intentional attempt to decieve :P And I think I've finally understood how the return value of scanf works since the last time I posted here, so my program can check to see if an integer was entered before processing the input, but I'm stuck on how to make the whole program start over if an integer is not entered. I have a hunch it would involve a loop, but I can't figure out how to make the program start over at "How many mb do you need converted?" if an integer is not entered into scanf..Here is the code I have so far:
Code:
#include <stdio.h>
int main () {
int b, mb, kb, Byte, kB, mB, gB;
char term;
}
[code]....
and my program makes the assumption for now at least, that mb will be inputted because that's the unit of measurement that i usually see advertised, and i didn't bother making an if statement to print a conversion in terms of gigabytes because i've never heard of a connection that fast :P
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Aug 10, 2013
I need a translate (in both directions) all primitive types, into char[] (will be stored in string)
I understand how to manipulate integral types with bits and I cant just cut them down and shift them, but float and double don't work with this manipulation. So, how I can create a perfect bit copy of float and double?
int i = 0xFCED03A4; //Random number
char c[4];
c[0] = ((i >> 3) & 0xFF);
c[1] = ((i >> 2) & 0xFF);
c[2] = ((i >> 1) & 0xFF);
c[1] = (i & 0xFF);
[Code]...
This is basic stuff but I need an equivalent for float and double types, and it needs to be a perfect BIT copy, not value copy.
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Nov 21, 2013
i want to ask how many bits are created when write this line
unsigned exponent:10;
is exponent locate a 10 byte from memory or 10 bits ?
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Dec 26, 2013
I tried to write a little bit of code to set all bits within a signed int with exception to the MSB, yielding the greatest max positive value. The odd part is that it works for shorts ints, and longs, which are 2, 4 and 4 bytes respectively, however long longs, with a size of 8 bytes, simply yields -1, which would indicate that it failed to clear the MSB. Heres the little segment in question:
template<typename T>
T getMax() {
return my::numerics<T>::is_signed ?
~0 ^ (1 << ((sizeof(T)*8)-1) ):
~0;
}
my::numerics is just an exercise- its thoroughly tested and I'm certain thats not the issue.
For shorts, ints, longs, this yields the maximum value. However, when I use it on long longs, the output is 0xFFFFFFFFFFFFFFFF, i.e. ~0. Obviously this means the maximum value for unsigned long longs, but -1 for signed long longs.
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Feb 27, 2013
IM SO CLOSE to finishing this program, how to sort out and drop the lowest int, between 8 ints. Is there any way I can do this? I have these ints:
grade1, grade2, grade3, grade4, grade5, grade6, grade7, grade8
My program already assigns them values. How can I find the lowest value and drop it?I literally do not know where to start, and this is the last thing I need *.*
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Oct 31, 2013
My problem is :
Code: numbers[10]={25,27,17,19,47,3,98,5,124,10};
You write a program at do below processes for above array.
You want a number 1 between 10 at user.
if user enter N value,program write to screen lowest N. number at array. For example user enter 2,program write to screen lowest secondary number of 5 value at array or user enter 10 value,program write to screen maximum number of 124 value at array.
But write the program with don't use sorting algorithm.
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Mar 18, 2013
I'm a C beginner. I have questions, let say if I have a structure of message containing of Id, Length, and 3 bytes of data, and I want to manually saved in individual bits of data, how can I do that? I confused on how to use typedef struct and union. Below is the sample code:
typedef struct {
uint8_t Id;
uint8_t Length;
uint8_t DataField[3];
}AA;
[Code] .....
By the way, the DataField is declared as above. It's not necessary for a data to be 24 bits. It can be bit 0 - bit 8, it can be bit 10 - bit 15 and so on. So, for each case, I want to ignore the other bits.
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Jul 14, 2014
I learned the bitwise operations in c, but how to shuffle the bits of the plain text accoring to DES's standard. Even with the key and the S-boxes. How DES is performed in C step by step. I have a fair knowledge in C.
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Nov 29, 2013
i want to assign number of bits by a variable in bitset? how to do that? like bitset<4> foo; instead of 4 i want to use some variable and later on by user i want to assign it! boost library or any other library!
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