.\" $OpenBSD: BN_zero.3,v 1.13 2023/04/30 19:23:54 tb Exp $
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.Dd $Mdocdate: April 30 2023 $
.Dt BN_ZERO 3
.Os
.Sh NAME
.Nm BN_zero ,
.Nm BN_one ,
.Nm BN_value_one ,
.Nm BN_set_word ,
.Nm BN_get_word
.Nd BIGNUM assignment operations
.Sh SYNOPSIS
.In openssl/bn.h
.Ft int
.Fo BN_zero
.Fa "BIGNUM *a"
.Fc
.Ft int
.Fo BN_one
.Fa "BIGNUM *a"
.Fc
.Ft const BIGNUM *
.Fo BN_value_one
.Fa void
.Fc
.Ft int
.Fo BN_set_word
.Fa "BIGNUM *a"
.Fa "BN_ULONG w"
.Fc
.Ft BN_ULONG
.Fo BN_get_word
.Fa "const BIGNUM *a"
.Fc
.Sh DESCRIPTION
.Vt BN_ULONG
is a macro that expands to an unsigned integral type optimized
for the most efficient implementation on the local platform.
It is
.Vt unsigned long Pq = Vt uint64_t
on
.Dv _LP64
platforms and
.Vt unsigned int Pq = Vt uint32_t
elsewhere.
.Pp
.Fn BN_zero ,
.Fn BN_one ,
and
.Fn BN_set_word
set
.Fa a
to the values 0, 1 and
.Fa w
respectively.
.Pp
.Fn BN_value_one
returns a
.Vt BIGNUM
constant of value 1.
This constant is useful for comparisons and assignments.
.Sh RETURN VALUES
.Fn BN_get_word
returns the value
.Fa a ,
or a number with all bits set if
.Fa a
cannot be represented as a
.Vt BN_ULONG .
.Pp
.Fn BN_zero ,
.Fn BN_one ,
and
.Fn BN_set_word
return 1 on success, 0 otherwise.
.Fn BN_value_one
returns the constant.
.Sh SEE ALSO
.Xr BN_bn2bin 3 ,
.Xr BN_new 3 ,
.Xr BN_set_bit 3 ,
.Xr BN_set_negative 3
.Sh HISTORY
.Fn BN_zero ,
.Fn BN_one ,
.Fn BN_value_one ,
and
.Fn BN_set_word
first appeared in SSLeay 0.5.1.
.Fn BN_get_word
first appeared in SSLeay 0.6.0.
These functions have been available since
.Ox 2.4 .
.Sh BUGS
Someone might change the constant.
.Pp
If the value of a
.Vt BIGNUM
is equal to a
.Vt BN_ULONG
with all bits set, the return value of
.Fn BN_get_word
collides with return value used to indicate errors.
.Pp
.Vt BN_ULONG
should probably be a typedef rather than a macro.