BN_SET_BIT(3) | Library Functions Manual | BN_SET_BIT(3)

# 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

library “libcrypto”
`#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_mask_bits`(BIGNUM *a, int n);

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

int
`BN_lshift1`(BIGNUM *r, const BIGNUM *a);

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

int
`BN_rshift1`(BIGNUM *r, const 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 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).

# SEE ALSO

BN_add(3), BN_new(3), BN_num_bytes(3), BN_set_negative(3), BN_zero(3)

# HISTORY

`BN_set_bit`(), `BN_clear_bit`(), `BN_is_bit_set`(), `BN_mask_bits`(), `BN_lshift`(), `BN_lshift1`(), `BN_rshift`(), and `BN_rshift1`() first appeared in SSLeay 0.5.1 and have been available since OpenBSD 2.4.

June 8, 2025 | Debian