Convert assignments from C ++ to C

I'm assuming that cacheconfig.numLines , cacheconfig.associativity , and cacheconfig.lineSize are unsigned int . If they are not, you may need a cast somewhere, or you can change them to be unsigned .

The first step is to arrange these common subexpressions in one place, and thereby define the variables a and b :

unsigned int a = log2(cacheconfig.numLines / cacheconfig.associativity);
unsigned int b = log2(cacheconfig.lineSize);
string binario = bitset<256>(address).to_string();
int InicioDado = 256 - b;
string dado = binario.substr(InicioDado, b);
int InicioIndex = InicioDado - a;
string index = binario.substr(InicioIndex, a);
int InicioTag = 256 - cacheconfig.lineSize;
string tag = binario.substr(InicioTag, 256 - InicioTag - b);
long unsigned int Tag = bitset<256>(tag).to_ulong();
long unsigned int Index = bitset<256>(index).to_ulong();
long unsigned int Dado = bitset<256>(dado).to_ulong();

Let's remove the variables of type int intermediary:

unsigned int a = log2(cacheconfig.numLines / cacheconfig.associativity);
unsigned int b = log2(cacheconfig.lineSize);
string binario = bitset<256>(address).to_string();
string dado = binario.substr(256 - b, b);
string index = binario.substr(256 - b - a, a);
string tag = binario.substr(256 - cacheconfig.lineSize, cacheconfig.lineSize - b);
long unsigned int Tag = bitset<256>(tag).to_ulong();
long unsigned int Index = bitset<256>(index).to_ulong();
long unsigned int Dado = bitset<256>(dado).to_ulong();

Now, let's see what it does. You get address , convert to a binary string using bitset , spike that string in some parts, and use bitset to convert those binary substrings to numbers later. Since this is a numerical calculation, I do not think it is ideal to use strings in it. This seems to be a task for bitwise operators << , >> and & .

First you get the last b bits, which are Dado . The%% of previous bits are a . The Index seems strange to me, but it's the last Tag bits except for the last cacheconfig.lineSize bits. This is strange because there is an intersection between b and Tag .

Well, to get the last Index bits of a number k , being x , we can do this:

x & ((1 << k) - 1)

To discard the last k >= 1 digits, we do this:

x >> k

Let's create some macros to make it easier (adding the parentheses around each parameter and macro as a whole to make them hygienic):

#define OBTER_ULTIMOS_BITS(x, k) ((x) & ((1 << (k)) - 1))
#define DESCARTAR_ULTIMOS_BITS(x, k) ((x) >> (k))

So, your code looks like this:

unsigned int a = log2(cacheconfig.numLines / cacheconfig.associativity);
unsigned int b = log2(cacheconfig.lineSize);
long unsigned int Tag = DESCARTAR_ULTIMOS_BITS(OBTER_ULTIMOS_BITS(address, cacheconfig.lineSize), b);
long unsigned int Index = DESCARTAR_ULTIMOS_BITS(OBTER_ULTIMOS_BITS(address, b + a), b);
long unsigned int Dado = OBTER_ULTIMOS_BITS(address, b);

And this code is the same in both C and C ++.

You may still need a function that (re) defines its k . Here is a implementation that I copied from this response . Just include it if you can not for some reason use the default implementation:

unsigned int log2(unsigned int x) {
    unsigned int resultado = 0;
    while (x >>= 1) resultado++;
    return resultado;
}