void
mulmid_fft_params (unsigned* lgK, unsigned* lgM, ulong* m1, ulong* m2,
ulong* p, size_t n1, size_t n2)
{
ZNP_ASSERT (n2 >= 1);
ZNP_ASSERT (n1 >= n2);
unsigned _lgM;
size_t _m1;
ulong M, _p;
// increase lgM until all the conditions are satisfied
for (_lgM = 1; ; _lgM++)
{
M = 1UL << _lgM;
_p = ((-n2) & (M/2 - 1)) + 1;
_m1 = CEIL_DIV_2EXP (n1 + _p, _lgM - 1);
if (_m1 <= 2 * M)
break;
}
*lgM = _lgM;
*lgK = (_m1 > M) ? (_lgM + 1) : _lgM;
*p = _p;
*m1 = _m1;
*m2 = CEIL_DIV_2EXP (n2, _lgM - 1);
}
void
zn_array_invert (ulong* res, const ulong* op, size_t n, const zn_mod_t mod)
{
ZNP_ASSERT (n >= 1);
// for now assume input is monic
ZNP_ASSERT (op[0] == 1);
if (n == 1)
{
res[0] = 1;
return;
}
size_t half = (n + 1) / 2; // ceil(n / 2)
// recursively obtain the first half of the output
zn_array_invert (res, op, half, mod);
// extend to second half of the output
if (mod->m & 1)
zn_array_invert_extend_fft (res + half, res, op, half, n - half, mod);
else
zn_array_invert_extend (res + half, res, op, half, n - half, mod);
}
/*
Helper function for ref_zn_array_unpack().
Inverse operation of ref_zn_array_pack_helper(); each output coefficient
occupies ceil(b / ULONG_BITS) ulongs.
Running time is soft-linear in output length.
*/
void
ref_zn_array_unpack_helper (ulong* res, const mpz_t op, size_t n, unsigned b,
unsigned k)
{
ZNP_ASSERT (n >= 1);
ZNP_ASSERT (mpz_sizeinbase (op, 2) <= n * b + k);
unsigned w = CEIL_DIV (b, ULONG_BITS);
mpz_t y;
mpz_init (y);
if (n == 1)
{
// base case
unsigned i;
mpz_tdiv_q_2exp (y, op, k);
for (i = 0; i < w; i++)
{
res[i] = mpz_get_ui (y);
mpz_tdiv_q_2exp (y, y, ULONG_BITS);
}
}
else
{
// recursively split into top and bottom halves
mpz_tdiv_q_2exp (y, op, (n / 2) * b + k);
ref_zn_array_unpack_helper (res + w * (n / 2), y, n - n / 2, b, 0);
mpz_tdiv_r_2exp (y, op, (n / 2) * b + k);
ref_zn_array_unpack_helper (res, y, n / 2, b, k);
}
mpz_clear (y);
}
void
zn_array_mulmid_fft_precomp1_init (zn_array_mulmid_fft_precomp1_t res,
const ulong* op1, size_t n1, size_t n2,
ulong x, const zn_mod_t mod)
{
ZNP_ASSERT (mod->m & 1);
ZNP_ASSERT (n2 >= 1);
ZNP_ASSERT (n1 >= n2);
res->n1 = n1;
res->n2 = n2;
unsigned lgK, lgM;
mulmid_fft_params (&lgK, &lgM, &res->m1, &res->m2, &res->p, n1, n2);
ulong M = 1UL << lgM;
ptrdiff_t skip = M + 1;
// allocate space for transposed IFFT
pmfvec_init (res->vec1, lgK, skip, lgM, mod);
// split input, with padding, in reversed order, and apply requested
// scaling factor
pmfvec_reverse (res->vec1, res->m1);
fft_split (res->vec1, op1, n1, res->p, x, 0);
pmfvec_reverse (res->vec1, res->m1);
// transposed IFFT first input
pmfvec_tpifft (res->vec1, res->m1, 0, res->m1, 0);
}
void
zn_array_mulmid_fft (ulong* res,
const ulong* op1, size_t n1,
const ulong* op2, size_t n2,
ulong x, const zn_mod_t mod)
{
ZNP_ASSERT (mod->m & 1);
ZNP_ASSERT (n2 >= 1);
ZNP_ASSERT (n1 >= n2);
// re-use the precomp1 code
zn_array_mulmid_fft_precomp1_t precomp;
zn_array_mulmid_fft_precomp1_init (precomp, op1, n1, n2, x, mod);
zn_array_mulmid_fft_precomp1_execute (res, op2, 1, precomp);
zn_array_mulmid_fft_precomp1_clear (precomp);
}
void
virtual_pmf_bfly (virtual_pmf_t op1, virtual_pmf_t op2)
{
ZNP_ASSERT (op1->parent == op2->parent);
struct virtual_pmfvec_struct* parent = op1->parent;
// op1 == 0
if (op1->index == -1)
{
virtual_pmf_set (op1, op2);
return;
}
// op2 == 0
if (op2->index == -1)
{
virtual_pmf_set (op2, op1);
virtual_pmf_rotate (op2, parent->M);
return;
}
virtual_pmf_isolate (op1);
virtual_pmf_isolate (op2);
pmf_t p1 = parent->buf[op1->index];
pmf_t p2 = parent->buf[op2->index];
p1[0] = op1->bias;
p2[0] = op2->bias;
pmf_bfly (p1, p2, parent->M, parent->mod);
}
void
virtual_pmf_sub (virtual_pmf_t res, virtual_pmf_t op)
{
ZNP_ASSERT (res->parent == op->parent);
struct virtual_pmfvec_struct* parent = res->parent;
// op == 0
if (op->index == -1)
return;
// res == 0
if (res->index == -1)
{
virtual_pmf_set (res, op);
virtual_pmf_rotate (res, parent->M);
return;
}
virtual_pmf_isolate (res);
pmf_t p2 = parent->buf[res->index];
pmf_t p1 = parent->buf[op->index];
p2[0] = res->bias;
p1[0] = op->bias;
pmf_sub (p2, p1, parent->M, parent->mod);
}
/*
tests zn_array_pack() once for given n, b, k
*/
int
testcase_zn_array_pack (size_t n, unsigned b, unsigned k)
{
ZNP_ASSERT (b >= 1);
ZNP_ASSERT (n >= 1);
int success = 1;
ulong* in = (ulong*) malloc (sizeof (ulong) * n);
size_t size = CEIL_DIV (n * b + k, GMP_NUMB_BITS);
mp_limb_t* res = (mp_limb_t*) malloc (sizeof (mp_limb_t) * (size + 2));
mp_limb_t* ref = (mp_limb_t*) malloc (sizeof (mp_limb_t) * (size + 2));
// sentries to check buffer overflow
res[0] = res[size + 1] = ref[0] = ref[size + 1] = 0x1234;
// generate random data: at most b bits per input coefficient, possibly less
unsigned rand_bits = (b >= ULONG_BITS) ? ULONG_BITS : b;
rand_bits = random_ulong (rand_bits) + 1;
ulong max = (rand_bits == ULONG_BITS)
? ((ulong)(-1)) : ((1UL << rand_bits) - 1);
size_t i;
for (i = 0; i < n; i++)
in[i] = random_ulong (max);
// run target and reference implementation
zn_array_pack (res + 1, in, n, 1, b, k, 0);
ref_zn_array_pack (ref + 1, in, n, b, k);
// check sentries
success = success && (res[0] == 0x1234);
success = success && (ref[0] == 0x1234);
success = success && (res[size + 1] == 0x1234);
success = success && (ref[size + 1] == 0x1234);
// check correct result
success = success && (mpn_cmp (res + 1, ref + 1, size) == 0);
free (ref);
free (res);
free (in);
return success;
}
unsigned
virtual_pmfvec_find_slot (virtual_pmfvec_t vec)
{
unsigned i;
for (i = 0; i < vec->max_buffers; i++)
if (!vec->buf[i])
return i;
// this should never happen; we always should have enough slots
ZNP_ASSERT (0);
}
void
zn_array_pack1 (mp_limb_t* res, const ulong* op, size_t n, ptrdiff_t s,
unsigned b, unsigned k, size_t r)
{
ZNP_ASSERT (b > 0 && b <= ULONG_BITS);
#if GMP_NAIL_BITS == 0 && ULONG_BITS == GMP_NUMB_BITS
// where to write the next limb
mp_limb_t* dest = res;
// write leading zero-padding
while (k >= ULONG_BITS)
{
*dest++ = 0;
k -= ULONG_BITS;
}
// limb currently being filled
mp_limb_t buf = 0;
// number of bits used in buf; always in [0, ULONG_BITS)
unsigned buf_b = k;
unsigned buf_b_old;
for (; n > 0; n--, op += s)
{
ZNP_ASSERT (b >= ULONG_BITS || *op < (1UL << b));
// put low bits of current input into buffer
buf += *op << buf_b;
buf_b_old = buf_b;
buf_b += b;
if (buf_b >= ULONG_BITS)
{
// buffer is full; flush it
*dest++ = buf;
buf_b -= ULONG_BITS;
// put remaining bits of current input into buffer
buf = buf_b_old ? (*op >> (ULONG_BITS - buf_b_old)) : 0;
}
}
void
zn_array_invert_extend (ulong* res, const ulong* approx, const ulong* op,
size_t n1, size_t n2, const zn_mod_t mod)
{
ZNP_ASSERT (n2 >= 1);
ZNP_ASSERT (n1 >= n2);
// The algorithm is basically newton iteration, inspired partly by the
// algorithm in [HZ04], as follows.
// Let f be the input series, of length n1 + n2.
// Let g be the current approximation to 1/f, of length n1.
// By newton iteration, (2*g - g*g*f) is a length n1 + n2 approximation
// to 1/f. Therefore the output of this function should be terms
// [n1, n1 + n2) of -g*g*f.
// We have g*f = 1 + h*x^n1 + O(x^(n1 + n2)), where h has length n2,
// i.e. h consists of terms [n1, n1 + n2) of g*f. Therefore h may be
// recovered as the middle product of f[1, n1 + n2) and g[0, n1).
// Then g*g*f = g + g*h*x^n1 + O(x^(n1 + n2)). Since g has length
// n1, the output is (the negative of) the first n2 coefficients of g*h.
// Compute h, put it in res[0, n2).
zn_array_mulmid (res, op + 1, n1 + n2 - 1, approx, n1, mod);
// Compute g * h, put it into a scratch buffer.
ZNP_FASTALLOC (temp, ulong, 6624, n1 + n2 - 1);
zn_array_mul (temp, approx, n1, res, n2, mod);
// Negate the first n2 coefficients of g * h into the output buffer.
zn_array_neg (res, temp, n2, mod);
ZNP_FASTFREE (temp);
}
void
merge_chunk_to_pmf (pmf_t res, const ulong* op, size_t n, size_t k, ulong M,
const zn_mod_t mod)
{
ZNP_ASSERT ((M & 1) == 0);
ulong r = (-res[0]) & (2*M - 1);
size_t end = k + M/2;
if (end > n)
end = n;
if (k >= end)
// nothing to do
return;
op += k;
ulong size = end - k;
// now we need to handle op[0, size), and we are guaranteed size <= M/2.
if (r < M)
{
if (size <= M - r)
zn_array_add_inplace (res + 1 + r, op, size, mod);
else
{
zn_array_add_inplace (res + 1 + r, op, M - r, mod);
// negacyclic wraparound:
zn_array_sub_inplace (res + 1, op + M - r, size - M + r, mod);
}
}
else
{
r -= M;
if (size <= M - r)
zn_array_sub_inplace (res + 1 + r, op, size, mod);
else
{
zn_array_sub_inplace (res + 1 + r, op, M - r, mod);
// negacyclic wraparound:
zn_array_add_inplace (res + 1, op + M - r, size - M + r, mod);
}
}
}
/*
Helper function for ref_zn_array_pack().
Sets x = 2^k * (op[0] + op[1]*2^b + ... + op[n-1]*2^((n-1)*b)).
Running time is soft-linear in output length.
*/
void
ref_zn_array_pack_helper (mpz_t x, const ulong* op, size_t n, unsigned b,
unsigned k)
{
ZNP_ASSERT (n >= 1);
if (n == 1)
{
// base case
mpz_set_ui (x, op[0]);
mpz_mul_2exp (x, x, k);
}
else
{
// recursively split into top and bottom halves
mpz_t y;
mpz_init (y);
ref_zn_array_pack_helper (x, op, n / 2, b, k);
ref_zn_array_pack_helper (y, op + n / 2, n - n / 2, b, 0);
mpz_mul_2exp (y, y, (n / 2) * b + k);
mpz_add (x, x, y);
mpz_clear (y);
}
}
void
zn_array_invert_extend_fft (ulong* res, const ulong* approx, const ulong* op,
size_t n1, size_t n2, const zn_mod_t mod)
{
ZNP_ASSERT (n2 >= 1);
ZNP_ASSERT (n1 >= n2);
ZNP_ASSERT (mod->m & 1);
// The algorithm here is the same as in zn_array_invert_extend(), except
// that we work with the FFTs directly. This allows us to save one FFT,
// since we use the FFT of g in both the middle product step and the
// product step.
// Determine FFT parameters for computing h = middle product of
// f[1, n1 + n2) and g[0, n1). (These parameters will also work for the
// subsequent product g * h.)
unsigned lgK, lgM;
ulong m1, m2, m3, p;
mulmid_fft_params (&lgK, &lgM, &m3, &m1, &p, n1 + n2 - 1, n1);
m2 = m3 - m1 + 1;
// We now have
// m1 = ceil(n1 / (M/2))
// = (n1 + p - 1) / (M/2).
// Therefore
// m3 = ceil((n1 + n2 - 1 + p) / (M/2))
// = ceil(n2 / (M/2)) + (n1 + p - 1) / (M/2)
// and
// m2 = ceil(n2 / (M/2)) + 1.
ulong M = 1UL << lgM;
ulong K = 1UL << lgK;
ptrdiff_t skip = M + 1;
pmfvec_t vec1, vec2;
pmfvec_init (vec1, lgK, skip, lgM, mod);
pmfvec_init (vec2, lgK, skip, lgM, mod);
// Find scaling factor that needs to be applied to both of the products
// below; takes into account the fudge from the pointwise multiplies, and
// the division by 2^lgK coming from the FFTs.
ulong x = pmfvec_mul_fudge (lgM, 0, mod);
x = zn_mod_mul (x, zn_mod_pow2 (-lgK, mod), mod);
// Split g[0, n1) into m1 coefficients, apply scaling factor, and compute
// m3 fourier coefficients, written to vec2.
fft_split (vec2, approx, n1, 0, x, 0);
pmfvec_fft (vec2, m3, m1, 0);
// Split f[1, n1 + n2) into m3 coefficients (in reversed order, with
// appropriate zero-padding), and compute transposed IFFT of length m3,
// written to vec1.
pmfvec_reverse (vec1, m3);
fft_split (vec1, op + 1, n1 + n2 - 1, p, 1, 0);
pmfvec_reverse (vec1, m3);
pmfvec_tpifft (vec1, m3, 0, m3, 0);
// Pointwise multiply the above FFT and transposed IFFT, into vec1.
pmfvec_mul (vec1, vec1, vec2, m3, 0);
// Transposed FFT vec1, obtaining m2 coefficients, then reverse and combine.
pmfvec_tpfft (vec1, m3, m2, 0);
pmfvec_reverse (vec1, m2);
fft_combine (res, n2, vec1, m2, 1);
pmfvec_reverse (vec1, m2);
// At this stage we have obtained the polynomial h in res[0, n2).
// Now we must compute h * g.
// Split h[0, n2) into m2 - 1 coefficients, and compute m3 - 1 fourier
// coefficients in vec1. For the splitting step, we set the bias to M,
// which effectively negates everything, so we're really computing the FFT
// of -h.
fft_split (vec1, res, n2, 0, 1, M);
pmfvec_fft (vec1, m3 - 1, m2 - 1, 0);
// Pointwise multiply that FFT with the first FFT of g into vec2.
pmfvec_mul (vec2, vec2, vec1, m3 - 1, 1);
pmfvec_clear (vec1);
// IFFT and combine, to obtain the product -h * g. We only need the low n2
// terms of the product (we throw away the high n1 - 1 terms).
pmfvec_ifft (vec2, m3 - 1, 0, m3 - 1, 0);
fft_combine (res, n2, vec2, m3 - 1, 0);
pmfvec_clear (vec2);
}
/*
Multiplication/squaring using Kronecker substitution at 2^b, -2^b,
2^(-b) and -2^(-b).
*/
void
zn_array_mul_KS4 (ulong* res,
const ulong* op1, size_t n1,
const ulong* op2, size_t n2,
int redc, const zn_mod_t mod)
{
ZNP_ASSERT (n2 >= 1);
ZNP_ASSERT (n1 >= n2);
ZNP_ASSERT (n1 <= ULONG_MAX);
ZNP_ASSERT ((mod->m & 1) || !redc);
if (n2 == 1)
{
// code below needs n2 > 1, so fall back on scalar multiplication
_zn_array_scalar_mul (res, op1, n1, op2[0], redc, mod);
return;
}
int sqr = (op1 == op2 && n1 == n2);
// bits in each output coefficient
unsigned bits = 2 * mod->bits + ceil_lg (n2);
// we're evaluating at x = B, -B, 1/B, -1/B,
// where B = 2^b, and b = ceil(bits / 4)
unsigned b = (bits + 3) / 4;
// number of ulongs required to store each base-B^2 digit
unsigned w = CEIL_DIV (2 * b, ULONG_BITS);
ZNP_ASSERT (w <= 2);
// Write f1(x) = f1e(x^2) + x * f1o(x^2)
// f2(x) = f2e(x^2) + x * f2o(x^2)
// h(x) = he(x^2) + x * ho(x^2)
// "e" = even, "o" = odd
size_t n1o = n1 / 2;
size_t n1e = n1 - n1o;
size_t n2o = n2 / 2;
size_t n2e = n2 - n2o;
size_t n3 = n1 + n2 - 1; // length of h
size_t n3o = n3 / 2;
size_t n3e = n3 - n3o;
// Put k1 = number of limbs needed to store f1(B) and |f1(-B)|.
// In f1(B), the leading coefficient starts at bit position b * (n1 - 1)
// and has length 2b, and the coefficients overlap so we need an extra bit
// for the carry: this gives (n1 + 1) * b + 1 bits. Ditto for f2.
size_t k1 = CEIL_DIV ((n1 + 1) * b + 1, GMP_NUMB_BITS);
size_t k2 = CEIL_DIV ((n2 + 1) * b + 1, GMP_NUMB_BITS);
size_t k3 = k1 + k2;
// allocate space
ZNP_FASTALLOC (limbs, mp_limb_t, 6624, 5 * k3);
mp_limb_t* v1_buf0 = limbs; // k1 limbs
mp_limb_t* v2_buf0 = v1_buf0 + k1; // k2 limbs
mp_limb_t* v1_buf1 = v2_buf0 + k2; // k1 limbs
mp_limb_t* v2_buf1 = v1_buf1 + k1; // k2 limbs
mp_limb_t* v1_buf2 = v2_buf1 + k2; // k1 limbs
mp_limb_t* v2_buf2 = v1_buf2 + k1; // k2 limbs
mp_limb_t* v1_buf3 = v2_buf2 + k2; // k1 limbs
mp_limb_t* v2_buf3 = v1_buf3 + k1; // k2 limbs
mp_limb_t* v1_buf4 = v2_buf3 + k2; // k1 limbs
mp_limb_t* v2_buf4 = v1_buf4 + k1; // k2 limbs
// arrange overlapping buffers to minimise memory use
// "p" = plus, "m" = minus
// "n" = normal order, "r" = reciprocal order
mp_limb_t* v1en = v1_buf0;
mp_limb_t* v1on = v1_buf1;
mp_limb_t* v1pn = v1_buf2;
mp_limb_t* v1mn = v1_buf0;
mp_limb_t* v2en = v2_buf0;
mp_limb_t* v2on = v2_buf1;
mp_limb_t* v2pn = v2_buf2;
mp_limb_t* v2mn = v2_buf0;
mp_limb_t* v3pn = v1_buf1;
mp_limb_t* v3mn = v1_buf2;
mp_limb_t* v3en = v1_buf0;
mp_limb_t* v3on = v1_buf1;
mp_limb_t* v1er = v1_buf2;
mp_limb_t* v1or = v1_buf3;
mp_limb_t* v1pr = v1_buf4;
mp_limb_t* v1mr = v1_buf2;
mp_limb_t* v2er = v2_buf2;
mp_limb_t* v2or = v2_buf3;
mp_limb_t* v2pr = v2_buf4;
mp_limb_t* v2mr = v2_buf2;
mp_limb_t* v3pr = v1_buf3;
mp_limb_t* v3mr = v1_buf4;
mp_limb_t* v3er = v1_buf2;
mp_limb_t* v3or = v1_buf3;
ZNP_FASTALLOC (z, ulong, 6624, 2 * w * (n3e + 1));
ulong* zn = z;
ulong* zr = z + w * (n3e + 1);
int v3m_neg;
// -------------------------------------------------------------------------
// "normal" evaluation points
if (!sqr)
{
// multiplication version
// evaluate f1e(B^2) and B * f1o(B^2)
// We need max(2 * b*n1e, 2 * b*n1o + b) bits for this packing step,
// which is safe since (n1 + 1) * b + 1 >= max(2 * b*n1e, 2 * b*n1o + b).
// Ditto for f2 below.
zn_array_pack (v1en, op1, n1e, 2, 2 * b, 0, k1);
zn_array_pack (v1on, op1 + 1, n1o, 2, 2 * b, b, k1);
// compute f1(B) = f1e(B^2) + B * f1o(B^2)
// and |f1(-B)| = |f1e(B^2) - B * f1o(B^2)|
ZNP_ASSERT_NOCARRY (mpn_add_n (v1pn, v1en, v1on, k1));
v3m_neg = signed_mpn_sub_n (v1mn, v1en, v1on, k1);
// evaluate f2e(B^2) and B * f2o(B^2)
zn_array_pack (v2en, op2, n2e, 2, 2 * b, 0, k2);
zn_array_pack (v2on, op2 + 1, n2o, 2, 2 * b, b, k2);
// compute f2(B) = f2e(B^2) + B * f2o(B^2)
// and |f2(-B)| = |f2e(B^2) - B * f2o(B^2)|
ZNP_ASSERT_NOCARRY (mpn_add_n (v2pn, v2en, v2on, k2));
v3m_neg ^= signed_mpn_sub_n (v2mn, v2en, v2on, k2);
// compute h(B) = f1(B) * f2(B)
// and |h(-B)| = |f1(-B)| * |f2(-B)|
// hn_neg is set if h(-B) is negative
ZNP_mpn_mul (v3pn, v1pn, k1, v2pn, k2);
ZNP_mpn_mul (v3mn, v1mn, k1, v2mn, k2);
}
else
{
// squaring version
// evaluate f1e(B^2) and B * f1o(B^2)
zn_array_pack (v1en, op1, n1e, 2, 2 * b, 0, k1);
zn_array_pack (v1on, op1 + 1, n1o, 2, 2 * b, b, k1);
// compute f1(B) = f1e(B^2) + B * f1o(B^2)
// and |f1(-B)| = |f1e(B^2) - B * f1o(B^2)|
ZNP_ASSERT_NOCARRY (mpn_add_n (v1pn, v1en, v1on, k1));
signed_mpn_sub_n (v1mn, v1en, v1on, k1);
// compute h(B) = f1(B)^2
// and h(-B) = |f1(-B)|^2
// hn_neg is cleared since h(-B) is never negative
ZNP_mpn_mul (v3pn, v1pn, k1, v1pn, k1);
ZNP_mpn_mul (v3mn, v1mn, k1, v1mn, k1);
v3m_neg = 0;
}
// Each coefficient of h(B) is up to 4b bits long, so h(B) needs at most
// ((n1 + n2 + 2) * b + 1) bits. (The extra +1 is to accommodate carries
// generated by overlapping coefficients.) The buffer has at least
// ((n1 + n2 + 2) * b + 2) bits. Therefore we can safely store 2*h(B) etc.
// compute 2 * he(B^2) = h(B) + h(-B)
// and B * 2 * ho(B^2) = h(B) - h(-B)
if (v3m_neg)
{
ZNP_ASSERT_NOCARRY (mpn_sub_n (v3en, v3pn, v3mn, k3));
ZNP_ASSERT_NOCARRY (mpn_add_n (v3on, v3pn, v3mn, k3));
}
else
{
ZNP_ASSERT_NOCARRY (mpn_add_n (v3en, v3pn, v3mn, k3));
ZNP_ASSERT_NOCARRY (mpn_sub_n (v3on, v3pn, v3mn, k3));
}
// -------------------------------------------------------------------------
// "reciprocal" evaluation points
// correction factors to take into account that if a polynomial has even
// length, its even and odd coefficients are swapped when the polynomial
// is reversed
unsigned a1 = (n1 & 1) ? 0 : b;
unsigned a2 = (n2 & 1) ? 0 : b;
unsigned a3 = (n3 & 1) ? 0 : b;
if (!sqr)
{
// multiplication version
// evaluate B^(n1-1) * f1e(1/B^2) and B^(n1-2) * f1o(1/B^2)
zn_array_pack (v1er, op1 + 2*(n1e - 1), n1e, -2, 2 * b, a1, k1);
zn_array_pack (v1or, op1 + 1 + 2*(n1o - 1), n1o, -2, 2 * b, b - a1, k1);
// compute B^(n1-1) * f1(1/B) =
// B^(n1-1) * f1e(1/B^2) + B^(n1-2) * f1o(1/B^2)
// and |B^(n1-1) * f1(-1/B)| =
// |B^(n1-1) * f1e(1/B^2) - B^(n1-2) * f1o(1/B^2)|
ZNP_ASSERT_NOCARRY (mpn_add_n (v1pr, v1er, v1or, k1));
v3m_neg = signed_mpn_sub_n (v1mr, v1er, v1or, k1);
// evaluate B^(n2-1) * f2e(1/B^2) and B^(n2-2) * f2o(1/B^2)
zn_array_pack (v2er, op2 + 2*(n2e - 1), n2e, -2, 2 * b, a2, k2);
zn_array_pack (v2or, op2 + 1 + 2*(n2o - 1), n2o, -2, 2 * b, b - a2, k2);
// compute B^(n2-1) * f2(1/B) =
// B^(n2-1) * f2e(1/B^2) + B^(n2-2) * f2o(1/B^2)
// and |B^(n1-1) * f2(-1/B)| =
// |B^(n2-1) * f2e(1/B^2) - B^(n2-2) * f2o(1/B^2)|
ZNP_ASSERT_NOCARRY (mpn_add_n (v2pr, v2er, v2or, k2));
v3m_neg ^= signed_mpn_sub_n (v2mr, v2er, v2or, k2);
// compute B^(n3-1) * h(1/B) =
// (B^(n1-1) * f1(1/B)) * (B^(n2-1) * f2(1/B))
// and |B^(n3-1) * h(-1/B)| =
// |B^(n1-1) * f1(-1/B)| * |B^(n2-1) * f2(-1/B)|
// hr_neg is set if h(-1/B) is negative
ZNP_mpn_mul (v3pr, v1pr, k1, v2pr, k2);
ZNP_mpn_mul (v3mr, v1mr, k1, v2mr, k2);
}
else
{
// squaring version
// evaluate B^(n1-1) * f1e(1/B^2) and B^(n1-2) * f1o(1/B^2)
zn_array_pack (v1er, op1 + 2*(n1e - 1), n1e, -2, 2 * b, a1, k1);
zn_array_pack (v1or, op1 + 1 + 2*(n1o - 1), n1o, -2, 2 * b, b - a1, k1);
// compute B^(n1-1) * f1(1/B) =
// B^(n1-1) * f1e(1/B^2) + B^(n1-2) * f1o(1/B^2)
// and |B^(n1-1) * f1(-1/B)| =
// |B^(n1-1) * f1e(1/B^2) - B^(n1-2) * f1o(1/B^2)|
ZNP_ASSERT_NOCARRY (mpn_add_n (v1pr, v1er, v1or, k1));
signed_mpn_sub_n (v1mr, v1er, v1or, k1);
// compute B^(n3-1) * h(1/B) = (B^(n1-1) * f1(1/B))^2
// and B^(n3-1) * h(-1/B) = |B^(n1-1) * f1(-1/B)|^2
// hr_neg is cleared since h(-1/B) is never negative
ZNP_mpn_mul (v3pr, v1pr, k1, v1pr, k1);
ZNP_mpn_mul (v3mr, v1mr, k1, v1mr, k1);
v3m_neg = 0;
}
// compute 2 * B^(n3-1) * he(1/B^2)
// = B^(n3-1) * h(1/B) + B^(n3-1) * h(-1/B)
// and 2 * B^(n3-2) * ho(1/B^2)
// = B^(n3-1) * h(1/B) - B^(n3-1) * h(-1/B)
if (v3m_neg)
{
ZNP_ASSERT_NOCARRY (mpn_sub_n (v3er, v3pr, v3mr, k3));
ZNP_ASSERT_NOCARRY (mpn_add_n (v3or, v3pr, v3mr, k3));
}
else
{
ZNP_ASSERT_NOCARRY (mpn_add_n (v3er, v3pr, v3mr, k3));
ZNP_ASSERT_NOCARRY (mpn_sub_n (v3or, v3pr, v3mr, k3));
}
// -------------------------------------------------------------------------
// combine "normal" and "reciprocal" information
// decompose he(B^2) and B^(2*(n3e-1)) * he(1/B^2) into base-B^2 digits
zn_array_unpack_SAFE (zn, v3en, n3e + 1, 2 * b, 1, k3);
zn_array_unpack_SAFE (zr, v3er, n3e + 1, 2 * b, a3 + 1, k3);
// combine he(B^2) and he(1/B^2) information to get even coefficients of h
zn_array_recover_reduce (res, 2, zn, zr, n3e, 2 * b, redc, mod);
// decompose ho(B^2) and B^(2*(n3o-1)) * ho(1/B^2) into base-B^2 digits
zn_array_unpack_SAFE (zn, v3on, n3o + 1, 2 * b, b + 1, k3);
zn_array_unpack_SAFE (zr, v3or, n3o + 1, 2 * b, b - a3 + 1, k3);
// combine ho(B^2) and ho(1/B^2) information to get odd coefficients of h
zn_array_recover_reduce (res + 1, 2, zn, zr, n3o, 2 * b, redc, mod);
ZNP_FASTFREE (z);
ZNP_FASTFREE (limbs);
}
/*
Multiplication/squaring using Kronecker substitution at 2^b.
*/
void
zn_array_mul_KS1 (ulong* res,
const ulong* op1, size_t n1,
const ulong* op2, size_t n2,
int redc, const zn_mod_t mod)
{
ZNP_ASSERT (n2 >= 1);
ZNP_ASSERT (n1 >= n2);
ZNP_ASSERT (n1 <= ULONG_MAX);
ZNP_ASSERT ((mod->m & 1) || !redc);
int sqr = (op1 == op2 && n1 == n2);
// length of h
size_t n3 = n1 + n2 - 1;
// bits in each output coefficient
unsigned b = 2 * mod->bits + ceil_lg (n2);
// number of ulongs required to store each output coefficient
unsigned w = CEIL_DIV (b, ULONG_BITS);
ZNP_ASSERT (w <= 3);
// number of limbs needed to store f1(2^b) and f2(2^b)
size_t k1 = CEIL_DIV (n1 * b, GMP_NUMB_BITS);
size_t k2 = CEIL_DIV (n2 * b, GMP_NUMB_BITS);
// allocate space
ZNP_FASTALLOC (limbs, mp_limb_t, 6624, 2 * (k1 + k2));
mp_limb_t* v1 = limbs; // k1 limbs
mp_limb_t* v2 = v1 + k1; // k2 limbs
mp_limb_t* v3 = v2 + k2; // k1 + k2 limbs
if (!sqr)
{
// multiplication version
// evaluate f1(2^b) and f2(2^b)
zn_array_pack (v1, op1, n1, 1, b, 0, 0);
zn_array_pack (v2, op2, n2, 1, b, 0, 0);
// compute h(2^b) = f1(2^b) * f2(2^b)
ZNP_mpn_mul (v3, v1, k1, v2, k2);
}
else
{
// squaring version
// evaluate f1(2^b)
zn_array_pack (v1, op1, n1, 1, b, 0, 0);
// compute h(2^b) = f1(2^b)^2
ZNP_mpn_mul (v3, v1, k1, v1, k1);
}
// unpack coefficients of h, and reduce mod m
ZNP_FASTALLOC (z, ulong, 6624, n3 * w);
zn_array_unpack_SAFE (z, v3, n3, b, 0, k1 + k2);
array_reduce (res, 1, z, n3, w, redc, mod);
ZNP_FASTFREE (z);
ZNP_FASTFREE (limbs);
}
/*
Multiplication/squaring using Kronecker substitution at 2^b and 2^(-b).
Note: this routine does not appear to be competitive in practice with the
other KS routines. It's here just for fun.
*/
void
zn_array_mul_KS3 (ulong* res,
const ulong* op1, size_t n1,
const ulong* op2, size_t n2,
int redc, const zn_mod_t mod)
{
ZNP_ASSERT (n2 >= 1);
ZNP_ASSERT (n1 >= n2);
ZNP_ASSERT (n1 <= ULONG_MAX);
ZNP_ASSERT ((mod->m & 1) || !redc);
int sqr = (op1 == op2 && n1 == n2);
// length of h
size_t n3 = n1 + n2 - 1;
// bits in each output coefficient
unsigned bits = 2 * mod->bits + ceil_lg (n2);
// we're evaluating at x = B and 1/B, where B = 2^b, and b = ceil(bits / 2)
unsigned b = (bits + 1) / 2;
// number of ulongs required to store each base-B digit
unsigned w = CEIL_DIV (b, ULONG_BITS);
ZNP_ASSERT (w <= 2);
// limbs needed to store f1(B) and B^(n1-1) * f1(1/B), ditto for f2
size_t k1 = CEIL_DIV (n1 * b, GMP_NUMB_BITS);
size_t k2 = CEIL_DIV (n2 * b, GMP_NUMB_BITS);
// allocate space
ZNP_FASTALLOC (limbs, mp_limb_t, 6624, 2 * (k1 + k2));
mp_limb_t* v1 = limbs; // k1 limbs
mp_limb_t* v2 = v1 + k1; // k2 limbs
mp_limb_t* v3 = v2 + k2; // k1 + k2 limbs
ZNP_FASTALLOC (z, ulong, 6624, 2 * w * (n3 + 1));
// "n" = normal order, "r" = reciprocal order
ulong* zn = z;
ulong* zr = z + w * (n3 + 1);
if (!sqr)
{
// multiplication version
// evaluate f1(B) and f2(B)
zn_array_pack (v1, op1, n1, 1, b, 0, k1);
zn_array_pack (v2, op2, n2, 1, b, 0, k2);
// compute h(B) = f1(B) * f2(B)
ZNP_mpn_mul (v3, v1, k1, v2, k2);
}
else
{
// squaring version
// evaluate f1(B)
zn_array_pack (v1, op1, n1, 1, b, 0, k1);
// compute h(B) = f1(B)^2
ZNP_mpn_mul (v3, v1, k1, v1, k1);
}
// decompose h(B) into base-B digits
zn_array_unpack_SAFE (zn, v3, n3 + 1, b, 0, k1 + k2);
if (!sqr)
{
// multiplication version
// evaluate B^(n1-1) * f1(1/B) and B^(n2-1) * f2(1/B)
zn_array_pack (v1, op1 + n1 - 1, n1, -1, b, 0, k1);
zn_array_pack (v2, op2 + n2 - 1, n2, -1, b, 0, k2);
// compute B^(n1+n2-2) * h(1/B) =
// (B^(n1-1) * f1(1/B)) * (B^(n2-1) * f2(1/B))
ZNP_mpn_mul (v3, v1, k1, v2, k2);
}
else
{
// squaring version
// evaluate B^(n1-1) * f1(1/B)
zn_array_pack (v1, op1 + n1 - 1, n1, -1, b, 0, k1);
// compute B^(2*n1-2) * h(1/B) = (B^(n1-1) * f1(1/B))^2
ZNP_mpn_mul (v3, v1, k1, v1, k1);
}
// decompose h(1/B) into base-B digits
zn_array_unpack_SAFE (zr, v3, n3 + 1, b, 0, k1 + k2);
// recover h(x) from h(B) and h(1/B)
// (note: need to check that the high digit of each output coefficient
// is < B - 1; this follows from an estimate in section 3.2 of [Har07].)
zn_array_recover_reduce (res, 1, zn, zr, n3, b, redc, mod);
ZNP_FASTFREE(z);
ZNP_FASTFREE(limbs);
}
/*
Multiplication/squaring using Kronecker substitution at 2^b and -2^b.
*/
void
zn_array_mul_KS2 (ulong* res,
const ulong* op1, size_t n1,
const ulong* op2, size_t n2,
int redc, const zn_mod_t mod)
{
ZNP_ASSERT (n2 >= 1);
ZNP_ASSERT (n1 >= n2);
ZNP_ASSERT (n1 <= ULONG_MAX);
ZNP_ASSERT ((mod->m & 1) || !redc);
if (n2 == 1)
{
// code below needs n2 > 1, so fall back on scalar multiplication
_zn_array_scalar_mul (res, op1, n1, op2[0], redc, mod);
return;
}
int sqr = (op1 == op2 && n1 == n2);
// bits in each output coefficient
unsigned bits = 2 * mod->bits + ceil_lg (n2);
// we're evaluating at x = B and -B, where B = 2^b, and b = ceil(bits / 2)
unsigned b = (bits + 1) / 2;
// number of ulongs required to store each output coefficient
unsigned w = CEIL_DIV (2 * b, ULONG_BITS);
ZNP_ASSERT (w <= 3);
// Write f1(x) = f1e(x^2) + x * f1o(x^2)
// f2(x) = f2e(x^2) + x * f2o(x^2)
// h(x) = he(x^2) + x * ho(x^2)
// "e" = even, "o" = odd
size_t n1o = n1 / 2;
size_t n1e = n1 - n1o;
size_t n2o = n2 / 2;
size_t n2e = n2 - n2o;
size_t n3 = n1 + n2 - 1; // length of h
size_t n3o = n3 / 2;
size_t n3e = n3 - n3o;
// f1(B) and |f1(-B)| are at most ((n1 - 1) * b + mod->bits) bits long.
// However, when evaluating f1e(B^2) and B * f1o(B^2) the bitpacking
// routine needs room for the last chunk of 2b bits. Therefore we need to
// allow room for (n1 + 1) * b bits. Ditto for f2.
size_t k1 = CEIL_DIV ((n1 + 1) * b, GMP_NUMB_BITS);
size_t k2 = CEIL_DIV ((n2 + 1) * b, GMP_NUMB_BITS);
size_t k3 = k1 + k2;
// allocate space
ZNP_FASTALLOC (limbs, mp_limb_t, 6624, 3 * k3);
mp_limb_t* v1_buf0 = limbs; // k1 limbs
mp_limb_t* v2_buf0 = v1_buf0 + k1; // k2 limbs
mp_limb_t* v1_buf1 = v2_buf0 + k2; // k1 limbs
mp_limb_t* v2_buf1 = v1_buf1 + k1; // k2 limbs
mp_limb_t* v1_buf2 = v2_buf1 + k2; // k1 limbs
mp_limb_t* v2_buf2 = v1_buf2 + k1; // k2 limbs
// arrange overlapping buffers to minimise memory use
// "p" = plus, "m" = minus
mp_limb_t* v1e = v1_buf0;
mp_limb_t* v2e = v2_buf0;
mp_limb_t* v1o = v1_buf1;
mp_limb_t* v2o = v2_buf1;
mp_limb_t* v1p = v1_buf2;
mp_limb_t* v2p = v2_buf2;
mp_limb_t* v1m = v1_buf0;
mp_limb_t* v2m = v2_buf0;
mp_limb_t* v3m = v1_buf1;
mp_limb_t* v3p = v1_buf0;
mp_limb_t* v3e = v1_buf2;
mp_limb_t* v3o = v1_buf0;
ZNP_FASTALLOC (z, ulong, 6624, w * n3e);
int v3m_neg;
if (!sqr)
{
// multiplication version
// evaluate f1e(B^2) and B * f1o(B^2)
zn_array_pack (v1e, op1, n1e, 2, 2 * b, 0, k1);
zn_array_pack (v1o, op1 + 1, n1o, 2, 2 * b, b, k1);
// evaluate f2e(B^2) and B * f2o(B^2)
zn_array_pack (v2e, op2, n2e, 2, 2 * b, 0, k2);
zn_array_pack (v2o, op2 + 1, n2o, 2, 2 * b, b, k2);
// compute f1(B) = f1e(B^2) + B * f1o(B^2)
// and f2(B) = f2e(B^2) + B * f2o(B^2)
ZNP_ASSERT_NOCARRY (mpn_add_n (v1p, v1e, v1o, k1));
ZNP_ASSERT_NOCARRY (mpn_add_n (v2p, v2e, v2o, k2));
// compute |f1(-B)| = |f1e(B^2) - B * f1o(B^2)|
// and |f2(-B)| = |f2e(B^2) - B * f2o(B^2)|
v3m_neg = signed_mpn_sub_n (v1m, v1e, v1o, k1);
v3m_neg ^= signed_mpn_sub_n (v2m, v2e, v2o, k2);
// compute h(B) = f1(B) * f2(B)
// compute |h(-B)| = |f1(-B)| * |f2(-B)|
// v3m_neg is set if h(-B) is negative
ZNP_mpn_mul (v3m, v1m, k1, v2m, k2);
ZNP_mpn_mul (v3p, v1p, k1, v2p, k2);
}
else
{
// squaring version
// evaluate f1e(B^2) and B * f1o(B^2)
zn_array_pack (v1e, op1, n1e, 2, 2 * b, 0, k1);
zn_array_pack (v1o, op1 + 1, n1o, 2, 2 * b, b, k1);
// compute f1(B) = f1e(B^2) + B * f1o(B^2)
ZNP_ASSERT_NOCARRY (mpn_add_n (v1p, v1e, v1o, k1));
// compute |f1(-B)| = |f1e(B^2) - B * f1o(B^2)|
signed_mpn_sub_n (v1m, v1e, v1o, k1);
// compute h(B) = f1(B)^2
// compute h(-B) = f1(-B)^2
// v3m_neg is cleared (since f1(-B)^2 is never negative)
ZNP_mpn_mul (v3m, v1m, k1, v1m, k1);
ZNP_mpn_mul (v3p, v1p, k1, v1p, k1);
v3m_neg = 0;
}
// he(B^2) and B * ho(B^2) are both at most b * (n3 + 1) bits long (since
// the coefficients don't overlap). The buffers used below are at least
// b * (n1 + n2 + 2) = b * (n3 + 3) bits long. So we definitely have
// enough room for 2 * he(B^2) and 2 * B * ho(B^2).
// compute 2 * he(B^2) = h(B) + h(-B)
ZNP_ASSERT_NOCARRY (v3m_neg ? mpn_sub_n (v3e, v3p, v3m, k3)
: mpn_add_n (v3e, v3p, v3m, k3));
// unpack coefficients of he, and reduce mod m
zn_array_unpack_SAFE (z, v3e, n3e, 2 * b, 1, k3);
array_reduce (res, 2, z, n3e, w, redc, mod);
// compute 2 * b * ho(B^2) = h(B) - h(-B)
ZNP_ASSERT_NOCARRY (v3m_neg ? mpn_add_n (v3o, v3p, v3m, k3)
: mpn_sub_n (v3o, v3p, v3m, k3));
// unpack coefficients of ho, and reduce mod m
zn_array_unpack_SAFE (z, v3o, n3o, 2 * b, b + 1, k3);
array_reduce (res + 1, 2, z, n3o, w, redc, mod);
ZNP_FASTFREE (z);
ZNP_FASTFREE (limbs);
}
void
virtual_pmfvec_ifft (virtual_pmfvec_t vec, ulong n, int fwd, ulong t)
{
ZNP_ASSERT (vec->lgK <= vec->lgM + 1);
ZNP_ASSERT (t * vec->K < 2 * vec->M);
ZNP_ASSERT (n + fwd <= vec->K);
if (vec->lgK == 0)
return;
vec->lgK--;
vec->K >>= 1;
const zn_mod_struct* mod = vec->mod;
virtual_pmf_t* data = vec->data;
ulong M = vec->M;
ulong K = vec->K;
ulong s, r = M >> vec->lgK;
long i;
if (n + fwd <= K)
{
for (i = K - 1; i >= (long) n; i--)
{
virtual_pmf_add (data[i], data[i + K]);
virtual_pmf_divby2 (data[i]);
}
virtual_pmfvec_ifft (vec, n, fwd, t << 1);
for (; i >= 0; i--)
{
virtual_pmf_add (data[i], data[i]);
virtual_pmf_sub (data[i], data[i + K]);
}
}
else
{
virtual_pmfvec_ifft (vec, K, 0, t << 1);
for (i = K - 1, s = t + r * i; i >= (long)(n - K); i--, s -= r)
{
virtual_pmf_sub (data[i + K], data[i]);
virtual_pmf_sub (data[i], data[i + K]);
virtual_pmf_rotate (data[i + K], M + s);
}
vec->data += K;
virtual_pmfvec_ifft (vec, n - K, fwd, t << 1);
vec->data -= K;
for (; i >= 0; i--, s -= r)
{
virtual_pmf_rotate (data[i + K], M - s);
virtual_pmf_bfly (data[i + K], data[i]);
}
}
vec->K <<= 1;
vec->lgK++;
}
void
zn_array_mul_fft_dft (ulong* res,
const ulong* op1, size_t n1,
const ulong* op2, size_t n2,
unsigned lgT, const zn_mod_t mod)
{
ZNP_ASSERT (mod->m & 1);
ZNP_ASSERT (n2 >= 1);
ZNP_ASSERT (n1 >= n2);
if (lgT == 0)
{
// no layers of DFT; just call usual FFT routine
int sqr = (op1 == op2) && (n1 == n2);
ulong x = zn_array_mul_fft_fudge (n1, n2, sqr, mod);
zn_array_mul_fft (res, op1, n1, op2, n2, x, mod);
return;
}
unsigned lgM, lgK;
// number of pmf_t coefficients for each input poly
ulong m1, m2;
// figure out how big the transform needs to be
mul_fft_params (&lgK, &lgM, &m1, &m2, n1, n2);
// number of pmf_t coefficients for output poly
ulong m = m1 + m2 - 1;
ulong M = 1UL << lgM;
ulong K = 1UL << lgK;
ptrdiff_t skip = M + 1;
size_t n3 = n1 + n2 - 1;
// Split up transform into length K = U * T, i.e. U columns and T rows.
if (lgT >= lgK)
lgT = lgK;
unsigned lgU = lgK - lgT;
ulong U = 1UL << lgU;
ulong T = 1UL << lgT;
// space for two input rows, and one partial row
pmfvec_t in1, in2, part;
pmfvec_init (in1, lgU, skip, lgM, mod);
pmfvec_init (in2, lgU, skip, lgM, mod);
pmfvec_init (part, lgU, skip, lgM, mod);
// the virtual pmfvec_t that we use for the column DFTs
virtual_pmfvec_t col;
virtual_pmfvec_init (col, lgT, lgM, mod);
// zero the output
zn_array_zero (res, n3);
long i, j, k;
int which;
// Write m = U * mT + mU, where 0 <= mU < U
ulong mU = m & (U - 1);
ulong mT = m >> lgU;
// for each row (beginning with the last partial row if it exists)....
for (i = mT - (mU == 0); i >= 0; i--)
{
ulong i_rev = bit_reverse (i, lgT);
// for each input array....
for (which = 0; which < 2; which++)
{
pmfvec_struct* in = which ? in2 : in1;
const ulong* op = which ? op2 : op1;
size_t n = which ? n2 : n1;
pmf_t p = in->data;
for (j = 0; j < U; j++, p += in->skip)
{
// compute the i-th row of the j-th column as it would look after
// the column FFTs, using naive DFT
pmf_zero (p, M);
ulong r = i_rev << (lgM - lgT + 1);
for (k = 0; k < T; k++)
{
merge_chunk_to_pmf (p, op, n, (k * U + j) << (lgM - 1), M, mod);
pmf_rotate (p, -r);
}
pmf_rotate (p, (i_rev * j) << (lgM - lgK + 1));
}
// Now we've got the whole row; run FFT on the row
pmfvec_fft (in, (i == mT) ? mU : U, U, 0);
}
if (i == mT)
{
// pointwise multiply the two partial rows
pmfvec_mul (part, in1, in2, mU, i == 0);
// remove fudge factor
pmfvec_scalar_mul (part, mU, pmfvec_mul_fudge (lgM, 0, mod));
// zero remainder of the partial row; we will subsequently add
// in contributions from the vertical IFFTs when we process the other
// rows.
for (j = mU; j < U; j++)
pmf_zero (part->data + part->skip * j, M);
}
else
{
// pointwise multiply the two rows
pmfvec_mul (in1, in1, in2, U, i == 0);
// remove fudge factor
pmfvec_scalar_mul (in1, U, pmfvec_mul_fudge (lgM, 0, mod));
// horizontal IFFT this row
pmfvec_ifft (in1, U, 0, U, 0);
// simulate vertical IFFTs with DFTs
for (j = 0; j < U; j++)
{
virtual_pmfvec_reset (col);
virtual_pmf_import (col->data[i], in1->data + in1->skip * j);
virtual_pmfvec_ifft (col, mT + (j < mU), (j >= mU) && mU,
j << (lgM + 1 - lgK));
if ((j >= mU) && mU)
{
// add contribution to partial row (only for rightmost columns)
pmf_t src = virtual_pmf_export (col->data[mT]);
if (src)
pmf_add (part->data + part->skip * j, src, M, mod);
}
// add contributions to output
for (k = 0; k < mT + (j < mU); k++)
merge_chunk_from_pmf (res, n3,
virtual_pmf_export (col->data[k]),
(k * U + j) * M/2, M, mod);
}
}
}
// now finish off the partial row
if (mU)
{
// horizontal IFFT partial row
pmfvec_ifft (part, mU, 0, U, 0);
// simulate leftmost vertical IFFTs
for (j = 0; j < mU; j++)
{
virtual_pmfvec_reset (col);
virtual_pmf_import (col->data[mT], part->data + part->skip * j);
virtual_pmfvec_ifft (col, mT + 1, 0, j << (lgM + 1 - lgK));
// add contributions to output
for (k = 0; k <= mT; k++)
merge_chunk_from_pmf (res, n3,
virtual_pmf_export (col->data[k]),
(k * U + j) * M/2, M, mod);
}
}
// normalise result
zn_array_scalar_mul (res, res, n3, zn_mod_pow2 (-lgK, mod), mod);
virtual_pmfvec_clear (col);
pmfvec_clear (part);
pmfvec_clear (in2);
pmfvec_clear (in1);
}
void zn_array_mul_fft (ulong* res,
const ulong* op1, size_t n1,
const ulong* op2, size_t n2,
ulong x, const zn_mod_t mod)
{
ZNP_ASSERT (mod->m & 1);
ZNP_ASSERT (n2 >= 1);
ZNP_ASSERT (n1 >= n2);
unsigned lgK, lgM;
// number of pmf_t coefficients for each input poly
ulong m1, m2;
// figure out how big the transform needs to be
mul_fft_params (&lgK, &lgM, &m1, &m2, n1, n2);
// number of pmf_t coefficients for output poly
ulong m3 = m1 + m2 - 1;
ulong M = 1UL << lgM;
ulong K = 1UL << lgK;
ptrdiff_t skip = M + 1;
pmfvec_t vec1, vec2;
int sqr = (op1 == op2 && n1 == n2);
if (!sqr)
{
// multiplying two distinct inputs
// split inputs into pmf_t's and perform FFTs
pmfvec_init (vec1, lgK, skip, lgM, mod);
fft_split (vec1, op1, n1, 0, 1, 0);
pmfvec_fft (vec1, m3, m1, 0);
// note: we apply the fudge factor here, because the second input is
// shorter than both the first input and the output :-)
pmfvec_init (vec2, lgK, skip, lgM, mod);
fft_split (vec2, op2, n2, 0, x, 0);
pmfvec_fft (vec2, m3, m2, 0);
// pointwise multiplication
pmfvec_mul (vec1, vec1, vec2, m3, 1);
pmfvec_clear (vec2);
}
else
{
// squaring a single input
// split input into pmf_t's and perform FFTs
pmfvec_init (vec1, lgK, skip, lgM, mod);
fft_split (vec1, op1, n1, 0, 1, 0);
pmfvec_fft (vec1, m3, m1, 0);
// pointwise multiplication
pmfvec_mul (vec1, vec1, vec1, m3, 1);
}
// inverse FFT, and write output
pmfvec_ifft (vec1, m3, 0, m3, 0);
size_t n3 = n1 + n2 - 1;
fft_combine (res, n3, vec1, m3, 0);
pmfvec_clear (vec1);
// if we're squaring, then we haven't applied the fudge factor yet,
// so do it now
if (sqr)
zn_array_scalar_mul_or_copy (res, res, n3, x, mod);
}
