Builtin functions of GCC compiler (original) (raw)

Last Updated : 30 Jan, 2023

These are four important built-in functions in GCC compiler:

1. __builtin_popcount(x)

This function is used to count the number of one's(set bits) in an integer.
Example:

if x = 4 binary value of 4 is 100 Output: No of ones is 1.

C `

// C program to illustrate _builtin_popcount(x)

#include <stdio.h> int main() { int n = 5;

printf("Count of 1s in binary of %d is %d ", n,
       __builtin_popcount(n));
return 0;

}

C++

// C++ program to illustrate _builtin_popcount(x)

#include <bits/stdc++.h> using namespace std;

int main() { int n = 5; cout << "Count of 1s in binary of " << n << " is " << __builtin_popcount(n); return 0; }

`

Output

Count of 1s in binary of 5 is 2

Time complexity : O(log2(n))
Auxiliary Space: O(1)

Note: Similarly you can use __builtin_popcountl(x) & __builtin_popcountll(x) for long and long long data types.

2 . __builtin_parity(x)

This function is used to check the parity of a number. This function returns true(1) if the number has odd parity else it returns false(0) for even parity.
Example:

if x = 7 7 has odd no. of 1's in its binary(111). Output: Parity of 7 is 1

C `

// C program to illustrate _builtin_parity(x)

#include <stdio.h> int main() { int n = 7;

printf("Parity of %d is %d ",
       n, __builtin_parity(n));
return 0;

}

C++

// C++ program to illustrate _builtin_parity(x)

#include <bits/stdc++.h> using namespace std;

int main() { int n = 7; cout << "Parity of " << n << " is " << __builtin_parity(n); return 0; }

`

Time complexity : O(log2(n))
Auxiliary Space: O(1)

Note: Similarly you can use __builtin_parityl(x) & __builtin_parityll(x) for long and long long data types.

3.__builtin_clz(x)

This function is used to count the leading zeros of the integer. Note : clz = count leading zero's.
Example: It counts number of zeros before the first occurrence of one(set bit).

a = 16 Binary form of 16 is 00000000 00000000 00000000 00010000 Output: 27

C `

// C program to illustrate __builtin_clz(x) #include <stdio.h> int main() { int n = 16;

printf("Count of leading zeros before 1 in %d is %d",
       n, __builtin_clz(n));
return 0;

}

C++

// C++ program to illustrate __builtin_clz(x) #include <bits/stdc++.h> using namespace std;

int main() { int n = 16; cout<<"Count of leading zeros before 1 in "<< n <<" is "<<__builtin_clz(n); return 0; }

`

Output

Count of leading zeros before 1 in 16 is 27

Time complexity : O(log2(n))
Auxiliary Space: O(1)
Note: __builtin_clz(x) This function only accept unsigned values
Note: Similarly you can use __builtin_clzl(x) & __builtin_clzll(x) for long and long long data types.

4.__builtin_ctz(x)

This function is used to count the trailing zeros of the given integer. Note : ctz = count trailing zeros.
Example: Count no of zeros from last to first occurrence of one(set bit).

a = 16 Binary form of 16 is 00000000 00000000 00000000 00010000 Output: ctz = 4

C `

// C program to illustrate __builtin_ctz(x) #include <stdio.h> int main() { int n = 16;

printf("Count of zeros from last to first "
       "occurrence of one is %d",
       __builtin_ctz(n));
return 0;

}

C++

// C++ program to illustrate __builtin_ctz(x) #include <bits/stdc++.h> using namespace std;

int main() { int n = 16; cout<<"Count of zeros from last to first occurrence of one is "<< __builtin_ctz(n); return 0; }

`

Output

Count of zeros from last to first occurrence of one is 4

Time complexity : O(log2(n))
Auxiliary Space: O(1)
Note: Similarly you can use __builtin_ctzl(x) & __builtin_ctzll(x) for long and long long data types.