public static int ge_frombytes_negate_vartime(out GroupElementP3 h, byte[] data, int offset)
{
FieldElement u, v, v3, vxx, check;
FieldOperations.fe_frombytes(out h.Y, data, offset);
FieldOperations.fe_1(out h.Z);
FieldOperations.fe_sq(out u, ref h.Y);
FieldOperations.fe_mul(out v, ref u, ref LookupTables.d);
FieldOperations.fe_sub(out u, ref u, ref h.Z); /* u = y^2-1 */
FieldOperations.fe_add(out v, ref v, ref h.Z); /* v = dy^2+1 */
FieldOperations.fe_sq(out v3, ref v);
FieldOperations.fe_mul(out v3, ref v3, ref v); /* v3 = v^3 */
FieldOperations.fe_sq(out h.X, ref v3);
FieldOperations.fe_mul(out h.X, ref h.X, ref v);
FieldOperations.fe_mul(out h.X, ref h.X, ref u); /* x = uv^7 */
FieldOperations.fe_pow22523(out h.X, ref h.X); /* x = (uv^7)^((q-5)/8) */
FieldOperations.fe_mul(out h.X, ref h.X, ref v3);
FieldOperations.fe_mul(out h.X, ref h.X, ref u); /* x = uv^3(uv^7)^((q-5)/8) */
FieldOperations.fe_sq(out vxx, ref h.X);
FieldOperations.fe_mul(out vxx, ref vxx, ref v);
FieldOperations.fe_sub(out check, ref vxx, ref u); /* vx^2-u */
if (FieldOperations.fe_isnonzero(ref check) != 0)
{
FieldOperations.fe_add(out check, ref vxx, ref u); /* vx^2+u */
if (FieldOperations.fe_isnonzero(ref check) != 0)
{
h = default(GroupElementP3);
return(-1);
}
FieldOperations.fe_mul(out h.X, ref h.X, ref LookupTables.sqrtm1);
}
if (FieldOperations.fe_isnegative(ref h.X) == (data[offset + 31] >> 7))
{
FieldOperations.fe_neg(out h.X, ref h.X);
}
FieldOperations.fe_mul(out h.T, ref h.X, ref h.Y);
return(0);
}
static void select(out GroupElementPreComp t, int pos, sbyte b)
{
GroupElementPreComp minust;
var bnegative = negative(b);
var babs = (byte)(b - (((-bnegative) & b) << 1));
ge_precomp_0(out t);
var table = LookupTables.Base[pos];
cmov(ref t, ref table[0], equal(babs, 1));
cmov(ref t, ref table[1], equal(babs, 2));
cmov(ref t, ref table[2], equal(babs, 3));
cmov(ref t, ref table[3], equal(babs, 4));
cmov(ref t, ref table[4], equal(babs, 5));
cmov(ref t, ref table[5], equal(babs, 6));
cmov(ref t, ref table[6], equal(babs, 7));
cmov(ref t, ref table[7], equal(babs, 8));
minust.yplusx = t.yminusx;
minust.yminusx = t.yplusx;
FieldOperations.fe_neg(out minust.xy2d, ref t.xy2d);
cmov(ref t, ref minust, bnegative);
}
