BN_mod_mul_reciprocal, BN_div_recp, BN_RECP_CTX_new, BN_RECP_CTX_free, BN_RECP_CTX_set - modular

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

3.5.0                                              2025-06-04                        BN_MOD_MUL_RECIPROCAL(3SSL)

BN_mod_mul_reciprocal() can be used to perform an efficient BN_mod_mul(3) operation when the operation
       will be performed repeatedly with the same modulus. It computes r=(a*b)%m using recp=1/m, which is set as
       described below.  ctx is a previously allocated BN_CTX used for temporary variables.

       BN_RECP_CTX_new() allocates and initializes a BN_RECP structure.

       BN_RECP_CTX_free() frees the components of the BN_RECP, and, if it was created by BN_RECP_CTX_new(), also
       the structure itself.  If recp is NULL, nothing is done.

       BN_RECP_CTX_set() stores m in recp and sets it up for computing 1/m and shifting it left by
       BN_num_bits(m)+1 to make it an integer. The result and the number of bits it was shifted left will later
       be stored in recp.

       BN_div_recp() divides a by m using recp. It places the quotient in dv and the remainder in rem.

       The BN_RECP_CTX structure cannot be shared between threads.

BN_RECP_CTX_init() was removed in OpenSSL 1.1.0

       BN_mod_mul_reciprocal, BN_div_recp, BN_RECP_CTX_new, BN_RECP_CTX_free, BN_RECP_CTX_set - modular
       multiplication using reciprocal

BN_RECP_CTX_new() returns the newly allocated BN_RECP_CTX, and NULL on error.

       BN_RECP_CTX_free() has no return value.

       For the other functions, 1 is returned for success, 0 on error.  The error codes can be obtained by
       ERR_get_error(3).

ERR_get_error(3), BN_add(3), BN_CTX_new(3)

        #include <openssl/bn.h>

        BN_RECP_CTX *BN_RECP_CTX_new(void);
        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_div_recp(BIGNUM *dv, BIGNUM *rem, const BIGNUM *a, BN_RECP_CTX *recp,
                        BN_CTX *ctx);

        int BN_mod_mul_reciprocal(BIGNUM *r, const BIGNUM *a, const BIGNUM *b,
                                  BN_RECP_CTX *recp, BN_CTX *ctx);