[#BN_mask_bits]
= BN_mask_bits
:mrdocs:

Truncate `a` in place so that only the least‐significant `n` bits remain.

== Synopsis

Declared in `<openssl/bn.h>`

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

== Return Value

1 on success, or 0 if `a` has fewer than `n` bits / on error.

== Parameters

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


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