template<int m> static inline Vector<ExactInt,m> to_exact(const Vector<Quantized,m>& x) {
Vector<ExactInt,m> r;
for (int i=0;i<m;i++) {
r[i] = ExactInt(x[i]);
assert(r[i]==x[i]); // Make sure the input is actually quantized
}
return r;
}
// Our fixed deterministic pseudorandom perturbation sequence. We limit ourselves to 32 bits so that we can pull four values out of a uint128_t.
template<int m> inline Vector<ExactInt,m> perturbation(const int level, const int i) {
static_assert(m<=4,"");
const int bits = min(exact::log_bound+1,128/4);
const auto limit = ExactInt(1)<<(bits-1);
const uint128_t noise = threefry(level,i);
Vector<ExactInt,m> result;
for (int a=0;a<m;a++)
result[a] = (cast_uint128<ExactInt>(noise>>32*a)&(2*limit-1))-limit;
return result;
}
static void predicate_tests() {
IntervalScope scope;
typedef Vector<double,2> TV2;
typedef Vector<Quantized,2> QV2;
// Compare triangle_oriented and incircle against approximate floating point versions
struct F {
static inline double triangle_oriented(const TV2 p0, const TV2 p1, const TV2 p2) {
return edet(p1-p0,p2-p0);
};
static inline double incircle(const TV2 p0, const TV2 p1, const TV2 p2, const TV2 p3) {
const auto d0 = p0-p3, d1 = p1-p3, d2 = p2-p3;
return edet(ROW(d0),ROW(d1),ROW(d2));
}
};
const auto random = new_<Random>(9817241);
for (int step=0;step<100;step++) {
#define MAKE(i) \
const auto p##i = tuple(i,QV2(random->uniform<Vector<ExactInt,2>>(-exact::bound,exact::bound))); \
const TV2 x##i(p##i.y);
MAKE(0) MAKE(1) MAKE(2) MAKE(3)
GEODE_ASSERT(triangle_oriented(p0,p1,p2)==(F::triangle_oriented(x0,x1,x2)>0));
GEODE_ASSERT(incircle(p0,p1,p2,p3)==(F::incircle(x0,x1,x2,x3)>0));
}
// Test behavior for large numbers, using the scale invariance and antisymmetry of incircle.
for (const int i : range(exact::log_bound)) {
const auto bound = ExactInt(1)<<i;
const auto p0 = tuple(0,QV2(-bound,-bound)), // Four points on a circle of radius sqrt(2)*bound
p1 = tuple(1,QV2( bound,-bound)),
p2 = tuple(2,QV2( bound, bound)),
p3 = tuple(3,QV2(-bound, bound));
GEODE_ASSERT(!incircle(p0,p1,p2,p3));
GEODE_ASSERT( incircle(p0,p1,p3,p2));
}
}
// Cast num/den to an int, rounding towards nearest. All inputs are destroyed. Take a sqrt if desired.
// The values array must consist of r numerators followed by one denominator.
void snap_divs(RawArray<Quantized> result, RawArray<mp_limb_t,2> values, const bool take_sqrt) {
assert(result.size()+1==values.m);
// For division, we seek x s.t.
// x-1/2 <= num/den <= x+1/2
// 2x-1 <= 2num/den <= 2x+1
// 2x-1 <= floor(2num/den) <= 2x+1
// 2x <= 1+floor(2num/den) <= 2x+2
// x <= (1+floor(2num/den))//2 <= x+1
// x = (1+floor(2num/den))//2
// In the sqrt case, we seek a nonnegative integer x s.t.
// x-1/2 <= sqrt(num/den) < x+1/2
// 2x-1 <= sqrt(4num/den) < 2x+1
// Now the leftmost and rightmost expressions are integral, so we can take floors to get
// 2x-1 <= floor(sqrt(4num/den)) < 2x+1
// Since sqrt is monotonic and maps integers to integers, floor(sqrt(floor(x))) = floor(sqrt(x)), so
// 2x-1 <= floor(sqrt(floor(4num/den))) < 2x+1
// 2x <= 1+floor(sqrt(floor(4num/den))) < 2x+2
// x <= (1+floor(sqrt(floor(4num/den))))//2 < x+1
// x = (1+floor(sqrt(floor(4num/den))))//2
// Thus, both cases look like
// x = (1+f(2**k*num/den))//2
// where k = 1 or 2 and f is some truncating integer op (division or division+sqrt).
// Adjust denominator to be positive
const auto raw_den = values[result.size()];
const bool den_negative = mp_limb_signed_t(raw_den.back())<0;
if (den_negative)
mpn_neg(raw_den.data(),raw_den.data(),raw_den.size());
const auto den = trim(raw_den);
assert(den.size()); // Zero should be prevented by the caller
// Prepare for divisions
const auto q = GEODE_RAW_ALLOCA(values.n-den.size()+1,mp_limb_t),
r = GEODE_RAW_ALLOCA(den.size(),mp_limb_t);
// Compute each component of the result
for (int i=0;i<result.size();i++) {
// Adjust numerator to be positive
const auto num = values[i];
const bool num_negative = mp_limb_signed_t(num.back())<0;
if (take_sqrt && num_negative!=den_negative && !num.contains_only(0))
throw RuntimeError("perturbed_ratio: negative value in square root");
if (num_negative)
mpn_neg(num.data(),num.data(),num.size());
// Add enough bits to allow round-to-nearest computation after performing truncating operations
mpn_lshift(num.data(),num.data(),num.size(),take_sqrt?2:1);
// Perform division
mpn_tdiv_qr(q.data(),r.data(),0,num.data(),num.size(),den.data(),den.size());
const auto trim_q = trim(q);
if (!trim_q.size()) {
result[i] = 0;
continue;
}
// Take sqrt if desired, reusing the num buffer
const auto s = take_sqrt ? sqrt_helper(num,trim_q) : trim_q;
// Verify that result lies in [-exact::bound,exact::bound];
const int ratio = sizeof(ExactInt)/sizeof(mp_limb_t);
static_assert(ratio<=2,"");
if (s.size() > ratio)
goto overflow;
const auto nn = ratio==2 && s.size()==2 ? s[0]|ExactInt(s[1])<<8*sizeof(mp_limb_t) : s[0],
n = (1+nn)/2;
if (uint64_t(n) > uint64_t(exact::bound))
goto overflow;
// Done!
result[i] = (num_negative==den_negative?1:-1)*Quantized(n);
}
return;
overflow:
throw OverflowError("perturbed_ratio: overflow in l'Hopital expansion");
}
