void fb_rdc_basic(fb_t c, dv_t a) {
int j, k;
dig_t *tmpa;
dv_t r;
dv_null(r);
TRY {
dv_new(r);
tmpa = a + FB_DIGS;
/* First reduce the high part. */
for (int i = fb_bits(tmpa) - 1; i >= 0; i--) {
if (fb_get_bit(tmpa, i)) {
SPLIT(k, j, i - FB_BITS, FB_DIG_LOG);
if (k <= 0) {
fb_addd_low(tmpa + j, tmpa + j, fb_poly_get(), FB_DIGS);
} else {
r[FB_DIGS] = fb_lshb_low(r, fb_poly_get(), k);
fb_addd_low(tmpa + j, tmpa + j, r, FB_DIGS + 1);
}
}
}
for (int i = fb_bits(a) - 1; i >= FB_BITS; i--) {
if (fb_get_bit(a, i)) {
SPLIT(k, j, i - FB_BITS, FB_DIG_LOG);
if (k == 0) {
fb_addd_low(a + j, a + j, fb_poly_get(), FB_DIGS);
} else {
r[FB_DIGS] = fb_lshb_low(r, fb_poly_get(), k);
fb_addd_low(a + j, a + j, r, FB_DIGS + 1);
}
}
}
fb_copy(c, a);
}
CATCH_ANY {
THROW(ERR_CAUGHT);
}
FINALLY {
fb_free(r);
}
}
void fb_invn_low(dig_t *c, const dig_t *a) {
int j, d, lu, lv, lt, l1, l2, bu, bv;
align dig_t _u[2 * FB_DIGS], _v[2 * FB_DIGS];
align dig_t _g1[2 * FB_DIGS], _g2[2 * FB_DIGS];
dig_t *t = NULL, *u = NULL, *v = NULL, *g1 = NULL, *g2 = NULL, carry;
dv_zero(_g1, FB_DIGS + 1);
dv_zero(_g2, FB_DIGS + 1);
u = _u;
v = _v;
g1 = _g1;
g2 = _g2;
/* u = a, v = f, g1 = 1, g2 = 0. */
dv_copy(u, a, FB_DIGS);
dv_copy(v, fb_poly_get(), FB_DIGS);
g1[0] = 1;
lu = lv = FB_DIGS;
l1 = l2 = 1;
bu = fb_bits(u);
bv = FB_BITS + 1;
j = bu - bv;
/* While (u != 1). */
while (1) {
/* If j < 0 then swap(u, v), swap(g1, g2), j = -j. */
if (j < 0) {
t = u;
u = v;
v = t;
lt = lu;
lu = lv;
lv = lt;
t = g1;
g1 = g2;
g2 = t;
lt = l1;
l1 = l2;
l2 = lt;
j = -j;
}
SPLIT(j, d, j, FB_DIG_LOG);
/* u = u + v * z^j. */
if (j > 0) {
carry = fb_lsha_low(u + d, v, j, lv);
u[d + lv] ^= carry;
} else {
fb_addd_low(u + d, u + d, v, lv);
}
/* g1 = g1 + g2 * z^j. */
if (j > 0) {
carry = fb_lsha_low(g1 + d, g2, j, l2);
l1 = (l2 + d >= l1 ? l2 + d : l1);
if (carry) {
g1[d + l2] ^= carry;
l1 = (l2 + d >= l1 ? l1 + 1 : l1);
}
} else {
fb_addd_low(g1 + d, g1 + d, g2, l2);
l1 = (l2 + d > l1 ? l2 + d : l1);
}
while (u[lu - 1] == 0)
lu--;
while (v[lv - 1] == 0)
lv--;
if (lu == 1 && u[0] == 1)
break;
/* j = deg(u) - deg(v). */
lt = util_bits_dig(u[lu - 1]) - util_bits_dig(v[lv - 1]);
j = ((lu - lv) << FB_DIG_LOG) + lt;
}
/* Return g1. */
fb_copy(c, g1);
}