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Unify SSE and AVX implementation of pexp

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This commit is contained in:
Gael Guennebaud
2018-11-26 16:36:19 +01:00
parent c2f35b1b47
commit cf8b85d5c5
6 changed files with 126 additions and 122 deletions
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65
Eigen/src/Core/arch/Default/GenericPacketMathFunctions.h
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@@ -9,7 +9,7 @@
// Public License v. 2.0. If a copy of the MPL was not distributed
// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
/* The log function of this file initially comes from
/* The exp and log functions of this file initially come from
* Julien Pommier's sse math library: http://gruntthepeon.free.fr/ssemath/
*/
@@ -25,12 +25,12 @@ namespace internal {
template <typename Packet>
EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS
EIGEN_UNUSED
Packet plog_float(const Packet _x) {
Packet plog_float(const Packet _x)
{
Packet x = _x;
const Packet cst_1 = pset1<Packet>(1.0f);
const Packet cst_half = pset1<Packet>(0.5f);
//const Packet cst_126f = pset1<Packet>(126.0f);
// The smallest non denormalized float number.
const Packet cst_min_norm_pos = pset1frombits<Packet>( 0x00800000u);
const Packet cst_minus_inf = pset1frombits<Packet>( 0xff800000u);
@@ -101,5 +101,64 @@ Packet plog_float(const Packet _x) {
return pselect(iszero_mask, cst_minus_inf, por(x, invalid_mask));
}
// Exponential function. Works by writing "x = m*log(2) + r" where
// "m = floor(x/log(2)+1/2)" and "r" is the remainder. The result is then
// "exp(x) = 2^m*exp(r)" where exp(r) is in the range [-1,1).
template <typename Packet>
EIGEN_DEFINE_FUNCTION_ALLOWING_MULTIPLE_DEFINITIONS
EIGEN_UNUSED
Packet pexp_float(const Packet _x)
{
const Packet cst_1 = pset1<Packet>(1.0f);
const Packet cst_half = pset1<Packet>(0.5f);
const Packet cst_exp_hi = pset1<Packet>( 88.3762626647950f);
const Packet cst_exp_lo = pset1<Packet>(-88.3762626647949f);
const Packet cst_cephes_LOG2EF = pset1<Packet>(1.44269504088896341f);
const Packet cst_cephes_exp_p0 = pset1<Packet>(1.9875691500E-4f);
const Packet cst_cephes_exp_p1 = pset1<Packet>(1.3981999507E-3f);
const Packet cst_cephes_exp_p2 = pset1<Packet>(8.3334519073E-3f);
const Packet cst_cephes_exp_p3 = pset1<Packet>(4.1665795894E-2f);
const Packet cst_cephes_exp_p4 = pset1<Packet>(1.6666665459E-1f);
const Packet cst_cephes_exp_p5 = pset1<Packet>(5.0000001201E-1f);
// Clamp x.
Packet x = pmax(pmin(_x, cst_exp_hi), cst_exp_lo);
// Express exp(x) as exp(m*ln(2) + r), start by extracting
// m = floor(x/ln(2) + 0.5).
Packet m = pfloor(pmadd(x, cst_cephes_LOG2EF, cst_half));
// Get r = x - m*ln(2). If no FMA instructions are available, m*ln(2) is
// subtracted out in two parts, m*C1+m*C2 = m*ln(2), to avoid accumulating
// truncation errors.
Packet r;
#ifdef EIGEN_HAS_SINGLE_INSTRUCTION_MADD
const Packet cst_nln2 = pset1<Packet>(-0.6931471805599453f);
r = pmadd(m, cst_nln2, x);
#else
const Packet cst_cephes_exp_C1 = pset1<Packet>(0.693359375f);
const Packet cst_cephes_exp_C2 = pset1<Packet>(-2.12194440e-4f);
r = psub(x, pmul(m, cst_cephes_exp_C1));
r = psub(r, pmul(m, cst_cephes_exp_C2));
#endif
Packet r2 = pmul(r, r);
// TODO(gonnet): Split into odd/even polynomials and try to exploit
// instruction-level parallelism.
Packet y = cst_cephes_exp_p0;
y = pmadd(y, r, cst_cephes_exp_p1);
y = pmadd(y, r, cst_cephes_exp_p2);
y = pmadd(y, r, cst_cephes_exp_p3);
y = pmadd(y, r, cst_cephes_exp_p4);
y = pmadd(y, r, cst_cephes_exp_p5);
y = pmadd(y, r2, r);
y = padd(y, cst_1);
// Return 2^m * exp(r).
return pmax(pldexp(y,m), _x);
}
} // end namespace internal
} // end namespace Eigen