Cryptography and SSL/TLS Toolkit



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


#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);


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 n is negative. An error is also returned if the internal representation of a is already shorter than n bits. The internal representation depends on the platform's word size, and this error can be safely ignored. Use BN_num_bits(3) to determine the exact number of bits if needed.

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.


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).


BN_num_bytes(3), BN_add(3)

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Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at