AVX swizzle broadcast and swap optimization #1213
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| constexpr batch_bool_constant<uint32_t, A, (V0 >= 4), (V1 >= 4), (V2 >= 4), (V3 >= 4), (V4 >= 4), (V5 >= 4), (V6 >= 4), (V7 >= 4)> lane_mask {}; | ||
| // select lane by the mask index divided by 4 | ||
| constexpr auto lane = batch_constant<uint32_t, A, 0, 0, 0, 0, 1, 1, 1, 1> {}; | ||
| constexpr int lane_idx = ((mask / make_batch_constant<uint32_t, 4, A>()) != lane).mask(); |
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I have difficulties seeing how the former lane_mask = V_i >= 4 is equivalent to V_i / 4 != lane[i].
Why isn't that just lane_mask >= make_batch_constant<uint32_t, 4, A>() ?
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Because r0 and r1 do not contain the same values as before:
- before:
r0contains items from low in both lanes andr1contains items from high in both lanes - after: each
r0lane contains items from its lane while eachr1lane contains items from the other lane.
For instance, before a 0 in the second lane must be selected from r0 (low values) while after it must be selected from r1 (other lane).
Contributor
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Because
r0andr1do not contain the same values as before:* before: `r0` contains items from low in both lanes and `r1` contains items from high in both lanes * after: each `r0` lane contains items from its lane while each `r1` lane contains items from the other lane.For instance, before a
0in the second lane must be selected fromr0(low values) while after it must be selected fromr1(other lane).
and this saves a few permute, perfect!
| constexpr batch_bool_constant<uint64_t, A, (V0 >= 2), (V1 >= 2), (V2 >= 2), (V3 >= 2)> blend_mask; | ||
| // select lane by the mask index divided by 2 | ||
| constexpr auto lane = batch_constant<uint64_t, A, 0, 0, 1, 1> {}; | ||
| constexpr int lane_idx = ((mask / make_batch_constant<uint64_t, 2, A>()) != lane).mask(); |
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Similar optimizations to #1201 but for AVX