- NAME
- SYNOPSIS
- DESCRIPTION
- RETURN VALUES
- SEE ALSO
- HISTORY

# 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 <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, 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 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.

# SEE ALSO

bn, BN_num_bytes, BN_add

# HISTORY

`BN_set_bit()`, `BN_clear_bit()`, `BN_is_bit_set()`, `BN_mask_bits()`, `BN_lshift()`, BN_lshift1(), `BN_rshift()`, and BN_rshift1() are available in all versions of SSLeay and OpenSSL.