## Linux and UNIX Man Pages

Test Your Knowledge in Computers #272
Difficulty: Easy
Alan Turing, while working at Bletchley, occasionally ran the 40 miles to London when he was needed for meetings there.
True or False?

# bn_is_one(3) [redhat man page]

```BN_cmp(3)							      OpenSSL								 BN_cmp(3)

NAME
BN_cmp, BN_ucmp, BN_is_zero, BN_is_one, BN_is_word, BN_is_odd - BIGNUM comparison and test functions

SYNOPSIS
#include <openssl/bn.h>

int BN_cmp(BIGNUM *a, BIGNUM *b);
int BN_ucmp(BIGNUM *a, BIGNUM *b);

int BN_is_zero(BIGNUM *a);
int BN_is_one(BIGNUM *a);
int BN_is_word(BIGNUM *a, BN_ULONG w);
int BN_is_odd(BIGNUM *a);

DESCRIPTION
BN_cmp() compares the numbers a and b. BN_ucmp() compares their absolute values.

BN_is_zero(), BN_is_one() and BN_is_word() test if a equals 0, 1, or w respectively. BN_is_odd() tests if a is odd.

BN_is_zero(), BN_is_one(), BN_is_word() and BN_is_odd() are macros.

RETURN VALUES
BN_cmp() returns -1 if a < b, 0 if a == b and 1 if a > b. BN_ucmp() is the same using the absolute values of a and b.

BN_is_zero(), BN_is_one() BN_is_word() and BN_is_odd() return 1 if the condition is true, 0 otherwise.

bn(3)

HISTORY
BN_cmp(), BN_ucmp(), BN_is_zero(), BN_is_one() and BN_is_word() are available in all versions of SSLeay and OpenSSL.  BN_is_odd() was added
in SSLeay 0.8.

0.9.7a								    2000-01-26								 BN_cmp(3)```

## Check Out this Related Man Page

```bn(3)								      OpenSSL								     bn(3)

NAME
bn - multiprecision integer arithmetics

SYNOPSIS
#include <openssl/bn.h>

BIGNUM *BN_new(void);
void BN_free(BIGNUM *a);
void BN_init(BIGNUM *);
void BN_clear(BIGNUM *a);
void BN_clear_free(BIGNUM *a);

BN_CTX *BN_CTX_new(void);
void BN_CTX_init(BN_CTX *c);
void BN_CTX_free(BN_CTX *c);

BIGNUM *BN_copy(BIGNUM *a, const BIGNUM *b);
BIGNUM *BN_dup(const BIGNUM *a);

BIGNUM *BN_swap(BIGNUM *a, BIGNUM *b);

int BN_num_bytes(const BIGNUM *a);
int BN_num_bits(const BIGNUM *a);
int BN_num_bits_word(BN_ULONG w);

int BN_add(BIGNUM *r, const BIGNUM *a, const BIGNUM *b);
int BN_sub(BIGNUM *r, const BIGNUM *a, const BIGNUM *b);
int BN_mul(BIGNUM *r, BIGNUM *a, BIGNUM *b, BN_CTX *ctx);
int BN_sqr(BIGNUM *r, BIGNUM *a, BN_CTX *ctx);
int BN_div(BIGNUM *dv, BIGNUM *rem, const BIGNUM *a, const BIGNUM *d,
BN_CTX *ctx);
int BN_mod(BIGNUM *rem, const BIGNUM *a, const BIGNUM *m, BN_CTX *ctx);
int BN_nnmod(BIGNUM *rem, const BIGNUM *a, const BIGNUM *m, BN_CTX *ctx);
int BN_mod_add(BIGNUM *ret, BIGNUM *a, BIGNUM *b, const BIGNUM *m,
BN_CTX *ctx);
int BN_mod_sub(BIGNUM *ret, BIGNUM *a, BIGNUM *b, const BIGNUM *m,
BN_CTX *ctx);
int BN_mod_mul(BIGNUM *ret, BIGNUM *a, BIGNUM *b, const BIGNUM *m,
BN_CTX *ctx);
int BN_mod_sqr(BIGNUM *ret, BIGNUM *a, const BIGNUM *m, BN_CTX *ctx);
int BN_exp(BIGNUM *r, BIGNUM *a, BIGNUM *p, BN_CTX *ctx);
int BN_mod_exp(BIGNUM *r, BIGNUM *a, const BIGNUM *p,
const BIGNUM *m, BN_CTX *ctx);
int BN_gcd(BIGNUM *r, BIGNUM *a, BIGNUM *b, BN_CTX *ctx);

int BN_add_word(BIGNUM *a, BN_ULONG w);
int BN_sub_word(BIGNUM *a, BN_ULONG w);
int BN_mul_word(BIGNUM *a, BN_ULONG w);
BN_ULONG BN_div_word(BIGNUM *a, BN_ULONG w);
BN_ULONG BN_mod_word(const BIGNUM *a, BN_ULONG w);

int BN_cmp(BIGNUM *a, BIGNUM *b);
int BN_ucmp(BIGNUM *a, BIGNUM *b);
int BN_is_zero(BIGNUM *a);
int BN_is_one(BIGNUM *a);
int BN_is_word(BIGNUM *a, BN_ULONG w);
int BN_is_odd(BIGNUM *a);

int BN_zero(BIGNUM *a);
int BN_one(BIGNUM *a);
const BIGNUM *BN_value_one(void);
int BN_set_word(BIGNUM *a, unsigned long w);
unsigned long BN_get_word(BIGNUM *a);

int BN_rand(BIGNUM *rnd, int bits, int top, int bottom);
int BN_pseudo_rand(BIGNUM *rnd, int bits, int top, int bottom);
int BN_rand_range(BIGNUM *rnd, BIGNUM *range);
int BN_pseudo_rand_range(BIGNUM *rnd, BIGNUM *range);

BIGNUM *BN_generate_prime(BIGNUM *ret, int bits,int safe, BIGNUM *add,
BIGNUM *rem, void (*callback)(int, int, void *), void *cb_arg);
int BN_is_prime(const BIGNUM *p, int nchecks,
void (*callback)(int, int, void *), BN_CTX *ctx, void *cb_arg);

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);

int BN_bn2bin(const BIGNUM *a, unsigned char *to);
BIGNUM *BN_bin2bn(const unsigned char *s, int len, BIGNUM *ret);
char *BN_bn2hex(const BIGNUM *a);
char *BN_bn2dec(const BIGNUM *a);
int BN_hex2bn(BIGNUM **a, const char *str);
int BN_dec2bn(BIGNUM **a, const char *str);
int BN_print(BIO *fp, const BIGNUM *a);
int BN_print_fp(FILE *fp, const BIGNUM *a);
int BN_bn2mpi(const BIGNUM *a, unsigned char *to);
BIGNUM *BN_mpi2bn(unsigned char *s, int len, BIGNUM *ret);

BIGNUM *BN_mod_inverse(BIGNUM *r, BIGNUM *a, const BIGNUM *n,
BN_CTX *ctx);

BN_RECP_CTX *BN_RECP_CTX_new(void);
void BN_RECP_CTX_init(BN_RECP_CTX *recp);
void BN_RECP_CTX_free(BN_RECP_CTX *recp);
int BN_RECP_CTX_set(BN_RECP_CTX *recp, const BIGNUM *m, BN_CTX *ctx);
int BN_mod_mul_reciprocal(BIGNUM *r, BIGNUM *a, BIGNUM *b,
BN_RECP_CTX *recp, BN_CTX *ctx);

BN_MONT_CTX *BN_MONT_CTX_new(void);
void BN_MONT_CTX_init(BN_MONT_CTX *ctx);
void BN_MONT_CTX_free(BN_MONT_CTX *mont);
int BN_MONT_CTX_set(BN_MONT_CTX *mont, const BIGNUM *m, BN_CTX *ctx);
BN_MONT_CTX *BN_MONT_CTX_copy(BN_MONT_CTX *to, BN_MONT_CTX *from);
int BN_mod_mul_montgomery(BIGNUM *r, BIGNUM *a, BIGNUM *b,
BN_MONT_CTX *mont, BN_CTX *ctx);
int BN_from_montgomery(BIGNUM *r, BIGNUM *a, BN_MONT_CTX *mont,
BN_CTX *ctx);
int BN_to_montgomery(BIGNUM *r, BIGNUM *a, BN_MONT_CTX *mont,
BN_CTX *ctx);

DESCRIPTION
This library performs arithmetic operations on integers of arbitrary size. It was written for use in public key cryptography, such as RSA
and Diffie-Hellman.

It uses dynamic memory allocation for storing its data structures.  That means that there is no limit on the size of the numbers manipu-
lated by these functions, but return values must always be checked in case a memory allocation error has occurred.

The basic object in this library is a BIGNUM. It is used to hold a single large integer. This type should be considered opaque and fields
should not be modified or accessed directly.

The creation of BIGNUM objects is described in BN_new(3); BN_add(3) describes most of the arithmetic operations.  Comparison is described
in BN_cmp(3); BN_zero(3) describes certain assignments, BN_rand(3) the generation of random numbers, BN_generate_prime(3) deals with prime
numbers and BN_set_bit(3) with bit operations. The conversion of BIGNUMs to external formats is described in BN_bn2bin(3).