# BN_set_bit

## Name

BN_set_bit, BN_clear_bit, BN_is_bit_set, BN_mask_bits, BN_lshift, BN_lshift1, BN_rshift, BN_rshift1 -- bit operations on BIGNUMs

## Synopsis

 `#include `
 ```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_mask_bits(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&lt;&lt;n)). The number is expanded if necessary.

BN_clear_bit() sets bit n in a to 0 (a&=~(1&lt;&lt;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)&gt;&gt;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 non-negative. 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 non-negative. 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).