[#BN_bn2mpi]
= BN_bn2mpi
:mrdocs:

Encode `a` in MPI format (4‐byte length prefix plus big‐endian content).

== Synopsis

Declared in `<openssl/bn.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
int
BN_bn2mpi(
    xref:BIGNUM.adoc[BIGNUM] const* a,
    unsigned char* to);
----

== Return Value

Number of bytes written (or required), including the length prefix.

== Parameters

[cols="1,4"]
|===
| Name| Description
| *a*
| Value to encode.
| *to*
| Output buffer, or NULL to return only the required length.
|===


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