OK thanks for that.

I think I found how to call `PDEP`

and `PEXT`

explicitly:

```
pdep(x::UInt32, y::UInt32) = ccall("llvm.x86.bmi.pdep.32", llvmcall, UInt32, (UInt32, UInt32), x, y)
pdep(x::UInt64, y::UInt64) = ccall("llvm.x86.bmi.pdep.64", llvmcall, UInt64, (UInt64, UInt64), x, y)
pext(x::UInt32, y::UInt32) = ccall("llvm.x86.bmi.pext.32", llvmcall, UInt32, (UInt32, UInt32), x, y)
pext(x::UInt64, y::UInt64) = ccall("llvm.x86.bmi.pext.64", llvmcall, UInt64, (UInt64, UInt64), x, y)
```

**Firstly, is this the right way?**

I modelled this on `pow_fast`

found in `fastmath.jl`

:

```
pow_fast(x::Float32, y::Integer) = ccall("llvm.powi.f32", llvmcall, Float32, (Float32, Int32), x, y)
pow_fast(x::Float64, y::Integer) = ccall("llvm.powi.f64", llvmcall, Float64, (Float64, Int32), x, y)
```

**Secondly, how can determine if a Julia build / hardware supports this instruction?**

Presumably attempting to execute these instructions on a non-supporting system will crash.

So I’d like to define some functions using these instructions only if supported, and use an alternative implementation otherwise.

```
if `PDEP` instruction supported
pdep(x::UInt32, y::UInt32) = ccall("llvm.x86.bmi.pdep.32", llvmcall, UInt32, (UInt32, UInt32), x, y)
pdep(x::UInt64, y::UInt64) = ccall("llvm.x86.bmi.pdep.64", llvmcall, UInt64, (UInt64, UInt64), x, y)
f(x,y) = pdep(x,y) ...
else
f(x,y) = # some other implementation
end
```