[#BN_mask_bits]
= BN&lowbar;mask&lowbar;bits
:mrdocs:

Truncate `a` in place so that only the least&hyphen;significant `n` bits remain&period;

== Synopsis

Declared in `&lt;openssl&sol;bn&period;h&gt;`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
int
BN&lowbar;mask&lowbar;bits(
    xref:BIGNUM.adoc[BIGNUM]* a,
    int n);
----

== Return Value

1 on success, or 0 if `a` has fewer than `n` bits &sol; on error&period;

== Parameters

[cols="1,4"]
|===
| Name| Description
| *a*
| BIGNUM to mask (modified)&period;
| *n*
| Number of low bits to keep&period;
|===


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