Builtin functions of GCC compiler
These are four important built-in functions in GCC compiler:
- __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; } |
Output:
Count of 1s in binary of 5 is 2
- Note: Similarly you can use __builtin_popcountl(x) & __builtin_popcountll(x) for long and long long data types.
- __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; } |
Output:
Parity of 7 is 1
- Note: Similarly you can use __builtin_parityl(x) & __builtin_parityll(x) for long and long long data types.
- __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; } |
Output:
Count of leading zeros before 1 in 16 is 27
- 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. - __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; } |
Output:
Count of zeros from last to first occurrence of one is 4
- Note: Similarly you can use __builtin_ctzl(x) & __builtin_ctzll(x) for long and long long data types.