Fastest algorithm to print all 16 bit binary numbers in Powershell?

tl; dr The following approach, using caching and array lookup, is faster, but may not be possible due to other bottlenecks.

Here's a version using caching. However, Measure-Command

there is no significant improvement (3.5 vs. 3.8 seconds elapsed) - I expected to see a much larger difference.

$l = @(0) * 256

0..255 | % {
    $l[$_] = "{0:D8}" -f [int64][convert]::ToString($_,2)
}

0 .. 65535 | % {
    $l[$_ / 256 ] + $l[$_ -band 255]   # no -shr in PS before 3.0
}

      

        
        
        
      

    

There are two "slow" parts to this problem. One is that the use is %{}

slower compared to a simple loop. Using the above modified to the next (which is not very useful) exits in 0.3 seconds.

For ($i = 0; $i -lt 65535; $i = $i + 1) {
    $line = $l[$i / 256 ] + $l[$i -band 255]
}

      

        
        
        
      

    

Whereas a similarly modified and equally useless version of the original completes in 0.5 seconds. This is slightly slower than the proposed cache version, although the proposed approach does not ultimately impact the bottleneck or wall clock.

For ($i = 0; $i -lt 65535; $i = $i + 1) {
    $line = "{0:D16}" -f [int64][convert]::ToString($i,2)
}

      

        
        
        
      

    

Using manual data collection with a given array is also much faster than %{}

and for my version it runs in 0.5 seconds - it will be slightly slower for the original approach, say 0.8 seconds.

$r = @("") * 65536
# ..
For ($i = 0; $i -lt 65535; $i = $i + 1) {
    $r[$i] = $l[$i / 256 ] + $l[$i -band 255]
}

      

        
        
        
      

    

Second, actually materializing with help is Write-Output

very slow and slower than collecting results with %{}

. Using Write-Output

or Write | Output-File ..

results in times longer than 8 seconds.

$r = @("") * 65536
$l = @(0) * 256

For ($i = 0; $i -lt 256; $i = $i + 1) {
    $l[$i] = "{0:D8}" -f [int64][convert]::ToString($i, 2)
}

For ($i = 0; $i -lt 65535; $i = $i + 1) {
    $r[$i] = $l[$i / 256 ] + $l[$i -band 255]
}

# to here in about 0.5 seconds
Write $r | Out-File results.txt

# almost another 8 seconds to get here