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copybara-service merged 1 commit into from
Jul 14, 2026
+12 −10
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Specify types to masks example easier to read #3213

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22 changes: 12 additions & 10 deletions hwy/examples/masks_and_logic.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -82,13 +82,15 @@ void RenderLineSIMD(size_t y, size_t width, int32_t* HWY_RESTRICT line_buf) {
const hn::ScalableTag<float> df;
const hn::RebindToSigned<decltype(df)> di; // int32_t tag

using MF = hn::Mask<decltype(df)>;
using MI = hn::Mask<decltype(di)>;
using VF = hn::Vec<decltype(df)>;
using VI = hn::Vec<decltype(di)>;

HWY_LANES_CONSTEXPR size_t N = hn::Lanes(df);

// Lambda for box mask
auto make_box_mask = [&](VF v_x, float y_val, Box b) HWY_ATTR {
auto make_box_mask = [&](VF v_x, float y_val, Box b) HWY_ATTR -> MF {
// Use AbsDiff to compute absolute difference.
VF v_bdx = hn::AbsDiff(v_x, hn::Set(df, b.cx));
VF v_bdy = hn::Set(df, std::abs(y_val - b.cy));
Expand All @@ -105,20 +107,20 @@ void RenderLineSIMD(size_t y, size_t width, int32_t* HWY_RESTRICT line_buf) {
// We can pass the start value directly to Iota.
VF v_x = hn::Iota(df, static_cast<float>(x));

auto mask1 = make_box_mask(v_x, static_cast<float>(y), kBox1);
auto mask2 = make_box_mask(v_x, static_cast<float>(y), kBox2);
MF mask1 = make_box_mask(v_x, static_cast<float>(y), kBox1);
MF mask2 = make_box_mask(v_x, static_cast<float>(y), kBox2);

// Combine masks using boolean operations.
// AndNot(a, b) means 'b AND NOT a'.
auto mask_both = hn::And(mask1, mask2);
auto mask1_only = hn::AndNot(mask2, mask1);
auto mask2_only = hn::AndNot(mask1, mask2);
MF mask_both = hn::And(mask1, mask2);
MF mask1_only = hn::AndNot(mask2, mask1);
MF mask2_only = hn::AndNot(mask1, mask2);

// Masks generated from floats cannot be directly used to select integers.
// RebindMask converts the mask representation to match the integer tag di.
auto imask_both = hn::RebindMask(di, mask_both);
auto imask1_only = hn::RebindMask(di, mask1_only);
auto imask2_only = hn::RebindMask(di, mask2_only);
MI imask_both = hn::RebindMask(di, mask_both);
MI imask1_only = hn::RebindMask(di, mask1_only);
MI imask2_only = hn::RebindMask(di, mask2_only);

// Chaining IfThenElse allows simulating nested if-else logic.
// The execution order is effectively reverse of chain order, or we can
Expand Down Expand Up @@ -158,7 +160,7 @@ static void CallRenderArtSIMD(size_t width, size_t height,

static void RenderArtScalar(size_t width, size_t height,
int32_t* HWY_RESTRICT buf) {
auto check_box = [](float x_val, float y_val, Box b) {
auto check_box = [](float x_val, float y_val, Box b) -> bool {
return std::abs(x_val - b.cx) < b.w && std::abs(y_val - b.cy) < b.h;
};

Expand Down
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