Adding fmaddsub#1136
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serge-sans-paille merged 1 commit intoxtensor-stack:masterfrom Jul 2, 2025
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| static constexpr bool get(unsigned const i, unsigned) noexcept { return (i & 1u) == 0; } | ||
| }; | ||
| const auto mask = make_batch_bool_constant<T, even_lane, A>(); | ||
| return fma(x, y, select(mask, neg(z), z)); |
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Is select a better option compared to a multiply?
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I think multiply is overly complicated. If we extend batch_constant to double (remove bitwise operators) then it might be worth it.
struct imag_neg {
static constexpr int get(const unsigned i, unsigned) noexcept { return (i & 1u) ? 1.0 : -1.0; }
};
// Generator first, then arch
const auto mask = xsimd::batch_cast<double>(xsimd::make_batch_constant<xsimd::as_integer_t<double>, imag_neg, arch>().as_batch());Also, I do not see a big difference on my machine:
(swizzle/multiply vs swizzle/select)
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thanks for going all the way down to the experiment!
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Hi all,
I have added support and tests for fmaddsub since it is useful in my scientific computations.
I tested it on x86 but I do not have access to arm/neon.
I proposed fmas but I have no strong opinion on the name of the function I picked something that seems to fit the style.
Let me know what you think and if/how we can get the new API included!
Thanks,
Marco