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 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

**_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 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

**__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 occurence of one(set bit).a = 16 Binary form of 16 is 00000000 00000000 00000000 00010000 Output: 27

`// 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**__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 occurence of one(set bit).a = 16 Binay form of 16 is 00000000 00000000 00000000 00010000 Output: ctz = 4

`// 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

`// C program to illustrate builtin functions of ` `// GCC compiler ` `#include <stdio.h> ` `#include <stdlib.h> ` ` ` `int` `main() ` `{ ` ` ` `int` `num = 4; ` ` ` `int` `clz = 0; ` ` ` `int` `ctz = 0; ` ` ` `int` `pop = 0; ` ` ` `int` `parity = 0; ` ` ` ` ` `pop = __builtin_popcount(num); ` ` ` `printf` `(` ```
"Number of one's in %d is %d
"
``` `, num, pop); ` ` ` ` ` `parity = __builtin_parity(num); ` ` ` `printf` `(` ```
"Parity of %d is %d
"
``` `, num, parity); ` ` ` ` ` `clz = __builtin_clz(num); ` ` ` `printf` `(` ```
"Number of leading zero's in %d is %d
"
``` `, num, clz); ` ` ` ` ` `// It only works for unsigned values ` ` ` `clz = __builtin_clz(-num); ` ` ` `printf` `(` ```
"Number of leading zero's in %d is %d
"
``` `, -num, clz); ` ` ` ` ` `ctz = __builtin_ctz(num); ` ` ` `printf` `(` ```
"Number of trailing zero's in %d is %d
"
``` `, num, ctz); ` ` ` ` ` `return` `0; ` `} ` |

**Output:**

Number of one's in 4 is 1 Parity of 4 is 1 Number of leading zero's in 4 is 29 Number of leading zero's in -4 is 0 Number of trailing zero's in 4 is 2

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