store bits(byte) in long long by concatenation - c

Question

poly8_bitslice() array if char as input, this input will be converted to bits(byte) by the function intToBits().
After the conversion I want to store the result in a long long variable. Is this possible?
Can I concatenate the result of intToBits()?
I want to do this with the following code:
#include <stdio.h>
#include <string.h>
#include <inttypes.h>
#include <string.h>
//#include <math.h>
typedef unsigned char poly8;
typedef unsigned long long poly8x64[8];
void intToBits(unsigned k, poly8 nk[8]) {
int i;
for(i=7;i>=0;i--){
nk[i] = (k%2);
k = (int)(k/2);
}
}
void poly8_bitslice(poly8x64 r, const poly8 x[64])
{
//TODO
int i;
for(i=0;i<64;i++){
poly8 xb[8];
intToBits(x[i], xb);
int j;
long long row;
for(j=0;j<8;j++){
row = row + x[j];
}
printf("row=%d \n", row);
}
}
int main()
{
poly8 a[64], b[64], r[64];
poly8x64 va, vb, vt;
int i;
FILE *urandom = fopen("/dev/urandom","r");
for(i=0;i<64;i++)
{
a[i] = fgetc(urandom);
b[i] = fgetc(urandom);
}
poly8_bitslice(va, a);
poly8_bitslice(vb, b);
fclose(urandom);
return 0;
}

Answer 1

I am not sure I fully understood your question but you can do something like this
char ch0 = 0xAA;
char ch1 = 0xBB;
char ch2 = 0xCC;
char ch3 = 0xDD;
long long int x = 0; // x is 0x00000000
x = (long long int)ch0; // x is 0x000000AA
x = x << 8; // x is 0x0000AA00
x = x | (long long int)ch1; // x is 0x0000AABB
x = x << 8; // x is 0x00AABB00
x = x | (long long int)ch2; // x is 0x00AABBCC
x = x << 8; // x is 0xAABBCC00
x = x | (long long int)ch3; // x is 0xAABBCCDD
In this case x would contain 0xAABBCCDD
The << operator will shift the content of the left hand operator by the number specified by the right hand operator. So 0xAA << 8 would become 0xAA00. Note that it will append zeros at the end while shifting.
The| operator will perform a bitwise or on both its operands. That is a bit by bit or. So the first bit of the left hand operator will be or'ed with the first bit of the right hand operator and the result will be placed in the first bit of the result.
Anything or'ed with zero results to its self so
0xAA00 | 0x00BB
would result in
0xAABB
In general a bit append function would be
long long int bitAppend(long long int x, char ch) {
return ((x << 8) | (long long int)ch);
}
This function would take the long long integer that you need to append to and the char to append to it and would return the appended long long int. Note that as soon as the 64 bits are filled up the high order bits will be shifted out.
For example
long long int x = 0x1122334455667788
x = x << 8; // x now is 0x2233445566778800
this would result into x being 0x2233445566778800 since there is only 64bits in a long long int so the high order bits had to move out.