1.) __builtin_popcount(x): Counts the number of one’s(set bits) in an integer(long/long long).
Ex- int x=5;
cout<<__builtin_popcount(x)<<endl; //returns 2.If x is of long type,we can use __builtin_popcountl(x) If x is of long long type,we can use __builtin_popcountll(x)
2.) __builtin_parity(x): Checks the Parity of a number.Returns true(1) if the number has odd parity(odd number of set bits) else it returns false(0) for even parity(even number of set bits).
Ex- int x=5;
cout<<__builtin_parity(x)<<endl; //returns 0.If x is of long type,we can use __builtin_parityl(x) If x is of long long type,we can use __builtin_parityll(x)
3.) __builtin_clz(x): Counts the leading number of zeros of the integer(long/long long).
If x is of long type,we can use __builtin_clzl(x) If x is of long long type,we can use __builtin_clzll(x)
Ex- int x=16; // 00000000 00000000 00000000 00010000 (32 bits)
cout<<__builtin_clz(x)<<endl; //returns 27.
Ex- long x=16; // 00000000 00000000 00000000 00010000 (32 bits)
cout<<__builtin_clzl(x)<<endl; //returns 27.
Ex- long long x=16; // 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00010000 (64 bits)
cout<<__builtin_clzll(x)<<endl; //returns 59.4.) __builtin_ctz(x): Counts the trailing number of zeros of the integer(long/long long).
If x is of long type,we can use __builtin_ctzl(x) If x is of long long type,we can use __builtin_ctzll(x)
Ex- int x=16; // 00000000 00000000 00000000 00010000 (32 bits)
cout<<__builtin_ctz(x)<<endl; //returns 4.In case of both __builtin_ctzl(x) and __builtin_ctzll(x),the answer is same.
There's also __builtin_ffs(x) (Find First Set) which returns (the index of the least significant bits of x) + 1.
There's also
__lg(x)which returns the index of the highest set bit.More about it.
So I need to find the leading zeroes of say 1e15 , and I used builtinclzll(x) , where x is initialized as long long data type , but at the end , the function returns the leading zeroes from the 32 bit representation. I also cross-verified it using builtinclzll(1e15) , but the result is still the same. help pls
the underscores were ignored , don't know why , but I used the correct function
got the mistake , really sorry to disturb you
Can someone explain me why i am getting 31 when i am calling __builtin_clz(0^0) as it should give 32. i am doing it using Z = l^r & then __builtin_clz(Z) it is giving 31 for l & r both zero.
cause (0 xor 0) is 1.
Bro how is 0^0 = 1 like bit wise 0 = ....0000 so its xor with another 0 will remain zero only, how will it become one.
RTFM
__builtin_clzcontains:"If x is 0, the result is undefined."
From GCC documentation, built-in function:
int __builtin_clz (unsigned int x)returns the number of leading 0-bits in x, starting at the most significant bit position. If x is 0, the result is undefined.