BN_CMP(3ossl)

Hii bestie!! Welcome to BN_CMP(3ossl) — the OpenSSL page for all the BIGNUM comparison and test functions. Buckle up, because these little math gremlins are lowkey iconic and you’re gonna understand every single one. 💅✨

🎀 NAME 🎀

Here’s the whole squad, no cap:

• BN_cmp
• BN_ucmp
• BN_is_zero
• BN_is_one
• BN_is_word
• BN_abs_is_word
• BN_is_odd
• BN_are_coprime

They’re all about BIGNUM comparison and test functions. Periodt. 💖

✨ SYNOPSIS ✨

First things first, bestie — pull in the header:

#include <openssl/bn.h>

Then here are the exact signatures, character for character:

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

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

int BN_are_coprime(BIGNUM *a, const BIGNUM *b, BN_CTX *ctx);

💖 DESCRIPTION 💖

Okay so, let’s break the crew down.

• BN_cmp() — compares the numbers a and b. Like a full vibe check on which one is bigger. 😌
• BN_ucmp() — compares their absolute values instead.
• BN_is_zero() — tests if a equals 0.
• BN_is_one() — tests if a equals 1.
• BN_is_word() — tests if a equals w.
• BN_abs_is_word() — tests if a equals |w|.
• BN_is_odd() — tests if a is odd.

And then there’s BN_are_coprime(), the main character: it determines if a and b are coprime. The ctx is used internally for storing temporary variables. The values of a and b and ctx must not be NULL.

Bestie, seriously: a, b, and ctx must not be NULL. That’s a hard no. 🫶

🌸 RETURN VALUES 🌸

• BN_cmp() — returns -1 if a < b, 0 if a == b, and 1 if a > b. 💅
• BN_ucmp() — same energy, but using the absolute values of a and b.
• BN_is_zero(), BN_is_one(), BN_is_word(), BN_abs_is_word() and BN_is_odd() — return 1 if the condition is true, 0 otherwise.
• BN_are_coprime() — returns 1 if the BIGNUMs are coprime, otherwise it returns 0.

🦋 HISTORY 🦋

Storytime, bestie:

• Prior to OpenSSL 1.1.0, BN_is_zero(), BN_is_one(), BN_is_word(), BN_abs_is_word() and BN_is_odd() were macros. The way they were macros before? Wild. 😭
• The function BN_are_coprime() was added in OpenSSL 3.1.

👑 COPYRIGHT 👑

Legal era, unfortunately, but we keep it cute:

Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.

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 <https://www.openssl.org/source/license.html>.

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Okay that’s the whole page, bestie. This one comes from OpenSSL 3.5.0, dated 2026-09-25, and its manual name is BN_CMP(3ossl). Mwah 💋✨