Cryptography Reference
In-Depth Information
if (i == -1)
{
cpy_l (rem_l, r_l);
SETZERO_L (quot_l);
return E_CLINT_OK ;
}
else if (i == 0)
{
SETONE_L (quot_l);
SETZERO_L (rem_l);
return E_CLINT_OK ;
}
In the next step we check whether the divisor has only one digit. In this case a
branch is made to a faster variant of division, which we shall discuss further below.
if (DIGITS_L (b_l) == 1)
goto shortdiv;
Now begins the actual division. First the scaling factor
d
is determined as the
exponent of a power of two. As long as
b
n
−
1
≥
BASEDIV2
:=
B/
2
, the most-
significant digit
b
n
−
1
of the divisor is shifted left by one bit, where
d
, beginning
with
d
=0
, is incremented by
1
. Furthermore, the pointer
msdptrb_l
is set to
the most-significant digit of the divisor. The value
BITPERDGT
− d
will be used
frequently in the sequel, and therefore it is saved in the variable
sbitsminusd
.
msdptrb_l = MSDPTR_L (b_l);
bn_1 = *msdptrb_l;
while (bn_1 < BASEDIV2)
{
d++;
bn_1 <<= 1;
}
sbitsminusd = (int)(BITPERDGT - d);
If
d>
0
, then the two most-significant digits
b
n
−
1
b
n
−
2
of
db
are computed and
stored in
bn_1
and
bn_2
. In this we must distinguish the two cases that the divisor
b
has exactly two, or more than two, digits. In the first case, binary zeros are inserted
into
b
n
−
2
from the right, while in the second case the least-significant digits of
b
n
−
2
come from
b
n
−
3
.
