Cryptography Reference
In-Depth Information
remainder modulo a power of
2
(reduction modulo
2
k
)
Function:
int mod2_l (CLINT d_l, ULONG k, CLINT r_l);
Syntax:
d_l
(dividend),
k
(exponent of the divisor or modulus)
Input:
Return:
r_l
(remainder)
int
mod2_l (CLINT d_l, ULONG k, CLINT r_l)
{
int i;
Since
2
k
>
0
, there is no test for division by
0
. First
d_l
is copied to
r_l
and a test
is made as to whether
k
exceeds the maximal binary length of a
CLINT
number, in
which case the function is terminated.
cpy_l (r_l, d_l);
if (k > CLINTMAXBIT)
return E_CLINT_OK;
The digit in
r_l
in which something changes is determined and is stored as an
index in
i
.If
i
is greater than the number of digits of
r_l
,thenwearedone.
i=1+(k>>LDBITPERDGT);
if (i > DIGITS_L (r_l))
return E_CLINT_OK;
Now the determined digit of
r_l
(counting from 1) is joined by a logical AND to
the value
2
k
mod
BITPERDGT
1
(
=2
k
mod16
1
in this implementation). The new
length
i
of
r_l
is stored in
r_l[0]
. After the removal of leading zeros the function
is terminated.
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