/**
* Multiply x[0:xlen-1] and y[0:ylen-1], and
* write the result to dest[0:xlen+ylen-1].
* The destination has to have space for xlen+ylen words,
* even if the result might be one limb smaller.
* This function requires that xlen >= ylen.
* The destination must be distinct from either input operands.
* All operands are unsigned.
* This function is basically the same gmp's mpn_mul. */
public static void mul(int[] dest,
int[] x, int xlen,
int[] y, int ylen)
{
dest[xlen] = MPN.mul_1(dest, x, xlen, y[0]);
for (int i = 1; i < ylen; i++)
{
long yword = (long)y[i] & 0xffffffffL;
long carry = 0;
for (int j = 0; j < xlen; j++)
{
carry += ((long)x[j] & 0xffffffffL) * yword
+ ((long)dest[i + j] & 0xffffffffL);
dest[i + j] = (int)carry;
carry = (long)(((ulong)carry) >> 32);
}
dest[i + xlen] = (int)carry;
}
}
public static int set_str(int[] dest, byte[] str, int str_len, int _base)
{
int size = 0;
if ((_base & (_base - 1)) == 0)
{
// The base is a power of 2. Read the input string from
// least to most significant character/digit. */
int next_bitpos = 0;
int bits_per_indigit = 0;
for (int i = _base; (i >>= 1) != 0;)
{
bits_per_indigit++;
}
int res_digit = 0;
for (int i = str_len; --i >= 0;)
{
int inp_digit = str[i];
res_digit |= inp_digit << next_bitpos;
next_bitpos += bits_per_indigit;
if (next_bitpos >= 32)
{
dest[size++] = res_digit;
next_bitpos -= 32;
res_digit = inp_digit >> (bits_per_indigit - next_bitpos);
}
}
if (res_digit != 0)
{
dest[size++] = res_digit;
}
}
else
{
// General case. The base is not a power of 2.
int indigits_per_limb = MPN.chars_per_word(_base);
int str_pos = 0;
while (str_pos < str_len)
{
int chunk = str_len - str_pos;
if (chunk > indigits_per_limb)
{
chunk = indigits_per_limb;
}
int res_digit = str[str_pos++];
int big_base = _base;
while (--chunk > 0)
{
res_digit = res_digit * _base + str[str_pos++];
big_base *= _base;
}
int cy_limb;
if (size == 0)
{
cy_limb = res_digit;
}
else
{
cy_limb = MPN.mul_1(dest, dest, size, big_base);
cy_limb += MPN.add_1(dest, dest, size, res_digit);
}
if (cy_limb != 0)
{
dest[size++] = cy_limb;
}
}
}
return(size);
}
