BN_mask_bits (3)

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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(3).

SEE ALSO

bn(3), BN_num_bytes(3), BN_add(3)

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.