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Use Lookup8 and detail::IsFull(d) in FastSigmoid 

Fix targeted for scalable architectures

PiperOrigin-RevId: 888633434
This commit is contained in:
Nikhil Dev Goyal 2026-03-24 06:36:37 -07:00 committed by Copybara-Service
parent 8a5e37eeb7
commit 259b757aef
1 changed files with 8 additions and 18 deletions
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26
ops/fast_ops-inl.h
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@ -76,7 +76,8 @@ HWY_INLINE hn::Vec<D> FastSigmoid(D d, hn::Vec<D> val) {
hn::Vec<D> b, c, d_coef;
if constexpr ((kLanes >= 4 && !HWY_HAVE_SCALABLE) ||
(HWY_HAVE_SCALABLE && sizeof(T) == 4)) {
(HWY_HAVE_SCALABLE && sizeof(T) == 4 &&
hn::detail::IsFull(d))) {
// Coefficients for P(y/2) ~ index using CF algo
const auto k0 = hn::Set(d, static_cast<T>(-0.1145426548151546));
const auto k1 = hn::Set(d, static_cast<T>(3.4556654973457404));
@ -118,23 +119,12 @@ HWY_INLINE hn::Vec<D> FastSigmoid(D d, hn::Vec<D> val) {
static_cast<T>(1.1565092321921886), static_cast<T>(-0.7540678688218365),
static_cast<T>(-3.767209600467866), static_cast<T>(-9.357047249878605)};
if constexpr (kLanes >= 8 && !HWY_HAVE_SCALABLE) {
auto idx = hn::IndicesFromVec(d, idx_i);
hn::CappedTag<T, 8> d8;
b = hn::TableLookupLanes(hn::ResizeBitCast(d, hn::Load(d8, arr_b)), idx);
c = hn::TableLookupLanes(hn::ResizeBitCast(d, hn::Load(d8, arr_c)), idx);
d_coef =
hn::TableLookupLanes(hn::ResizeBitCast(d, hn::Load(d8, arr_d)), idx);
} else {
auto idx = hn::IndicesFromVec(d, idx_i);
hn::FixedTag<T, 4> d4;
b = hn::TwoTablesLookupLanes(d, hn::Load(d4, arr_b),
hn::Load(d4, arr_b + 4), idx);
c = hn::TwoTablesLookupLanes(d, hn::Load(d4, arr_c),
hn::Load(d4, arr_c + 4), idx);
d_coef = hn::TwoTablesLookupLanes(d, hn::Load(d4, arr_d),
hn::Load(d4, arr_d + 4), idx);
}
// Since Lookup8 is available for HWY_MIN_BYTES / sizeof(T) >= 4, this
// condition covers all cases we encounter inside the top level if block
// inside FastSigmoid
b = hn::Lookup8(d, arr_b, idx_i);
c = hn::Lookup8(d, arr_c, idx_i);
d_coef = hn::Lookup8(d, arr_d, idx_i);
} else {
// --- FALLBACK PATH: Blend Chain ---
// Thresholds for intervals