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Add more tests for pow and fix a corner case for huge exponent where the result is always zero or infinite unless x is one.

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This commit is contained in:
Rasmus Munk Larsen
2021-02-05 16:58:49 -08:00
parent abcde69a79
commit 6e3b795f81
2 changed files with 32 additions and 10 deletions
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17
Eigen/src/Core/arch/Default/GenericPacketMathFunctions.h
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@@ -929,6 +929,11 @@ Packet generic_pow(const Packet& x, const Packet& y) {
Packet y_is_pos = pandnot(ptrue(y), por(y_is_zero, y_is_neg));
Packet y_is_nan = pandnot(ptrue(y), pcmp_eq(y, y));
Packet abs_y_is_inf = pcmp_eq(pabs(y), cst_pos_inf);
// |y| is so large that (1+eps)^y over- or underflows.
EIGEN_CONSTEXPR Scalar huge_exponent =
(std::numeric_limits<Scalar>::digits * Scalar(EIGEN_LOG2E)) /
std::numeric_limits<Scalar>::epsilon();
Packet abs_y_is_huge = pcmp_lt(pset1<Packet>(huge_exponent), pabs(y));
// Predicates for whether y is integer and/or even.
Packet y_is_int = pcmp_eq(pfloor(y), y);
@@ -937,14 +942,16 @@ Packet generic_pow(const Packet& x, const Packet& y) {
// Predicates encoding special cases for the value of pow(x,y)
Packet invalid_negative_x = pandnot(pandnot(pandnot(x_is_neg, abs_x_is_inf), y_is_int), abs_y_is_inf);
Packet pow_is_one = por(por(x_is_one, y_is_zero),
pand(x_is_neg_one,
por(abs_y_is_inf, pandnot(y_is_even, invalid_negative_x))));
Packet pow_is_nan = por(invalid_negative_x, por(x_is_nan, y_is_nan));
Packet pow_is_one = por(por(y_is_zero, x_is_one), pand(x_is_neg_one, abs_y_is_inf));
Packet pow_is_zero = por(por(por(pand(x_is_zero, y_is_pos), pand(abs_x_is_inf, y_is_neg)),
pand(pand(abs_x_is_lt_one, abs_y_is_inf), y_is_pos)),
pand(pand(abs_x_is_gt_one, abs_y_is_inf), y_is_neg));
pand(pand(abs_x_is_lt_one, abs_y_is_huge), y_is_pos)),
pand(pand(abs_x_is_gt_one, abs_y_is_huge), y_is_neg));
Packet pow_is_inf = por(por(por(pand(x_is_zero, y_is_neg), pand(abs_x_is_inf, y_is_pos)),
pand(pand(abs_x_is_lt_one, abs_y_is_inf), y_is_neg)),
pand(pand(abs_x_is_gt_one, abs_y_is_inf), y_is_pos));
pand(pand(abs_x_is_lt_one, abs_y_is_huge), y_is_neg)),
pand(pand(abs_x_is_gt_one, abs_y_is_huge), y_is_pos));
// General computation of pow(x,y) for positive x or negative x and integer y.
Packet negate_pow_abs = pandnot(x_is_neg, y_is_even);