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Add rsqrt method to Float trait #343

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davll opened this issue Nov 9, 2017 · 4 comments
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Add rsqrt method to Float trait #343

davll opened this issue Nov 9, 2017 · 4 comments

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@davll
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davll commented Nov 9, 2017 •
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rsqrt is a widely used math function in game development, and is faster than combining the two functions: recip(sqrt(x)) thanks to x86 SSE instructions RSQRTSS, RSQRTPS, RSQRTSD, and RSQRTPD. Should we consider add rsqrt to Float trait?

  • x86/x86_64 SSE: _mm_rsqrt_ps (note that RSQRT instruction is approximate, less accurate than SQRT)
  • ARM Neon VRSQRTE
  • PowerPC Altivec: vec_rsqrte
@cuviper
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cuviper commented Nov 10, 2017

This should probably be proposed for the standard library first. So far we don't have any arch-specific code -- I'd rather just have num's impl Float for f64 forward to an optimized/intrinsic call in std.

@clarfonthey
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I agree; it makes sense to offer this in libstd.

@davll
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davll commented Nov 10, 2017

Reasonable, I'll propose it in rust-lang/rust.
I'll keep the issue open as reminder.

@cuviper cuviper mentioned this issue Dec 19, 2017
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cuviper commented Dec 19, 2017

This issue was moved to rust-num/num-traits#1

@cuviper cuviper closed this as completed Dec 19, 2017
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@cuviper @davll @clarfonthey