# BN_set_bit.3ssl - Man Page

bit operations on BIGNUMs

## Synopsis

``` #include <openssl/bn.h>

int BN_set_bit(BIGNUM *a, int n);
int BN_clear_bit(BIGNUM *a, int n);

int BN_is_bit_set(const BIGNUM *a, int n);

int BN_lshift(BIGNUM *r, const BIGNUM *a, int n);
int BN_lshift1(BIGNUM *r, BIGNUM *a);

int BN_rshift(BIGNUM *r, BIGNUM *a, int n);
int BN_rshift1(BIGNUM *r, BIGNUM *a);```

## Description

BN_set_bit() sets bit n in a to 1 (`a|=(1<<n)`). The number is expanded if necessary.

BN_clear_bit() sets bit n in a to 0 (`a&=~(1<<n)`). An error occurs if a is shorter than n bits.

BN_is_bit_set() tests if bit n in a is set.

BN_mask_bits() truncates a to an n bit number (`a&=~((~0)<<n)`).  An error occurs if a already is shorter than n bits.

BN_lshift() shifts a left by n bits and places the result in r (`r=a*2^n`). Note that n must be nonnegative. BN_lshift1() shifts a left by one and places the result in r (`r=2*a`).

BN_rshift() shifts a right by n bits and places the result in r (`r=a/2^n`). Note that n must be nonnegative. BN_rshift1() shifts a right by one and places the result in r (`r=a/2`).

For the shift functions, r and a may be the same variable.

## Return Values

BN_is_bit_set() returns 1 if the bit is set, 0 otherwise.

All other functions return 1 for success, 0 on error. The error codes can be obtained by ERR_get_error(3).