How can I convert hexadecimal fraction to decimal in PowerShell? - powershell

Question

Is there a way to convert hexadecimal fractions (i.e.: numbers with values <1.0, represented in hex) into their decimal equivalents in PowerShell?
Examples:
Hex Dec
0.0858b9da24fb4cac = 0.032603851087498366
0.8c3115559ab0c10b = 0.5476239522928976
Guides I've found for general HEX/DEC conversion say to use [Convert], which is fine for whole numbers, but it seems to completely fail when I throw a decimal point in the string.
Note: Examples were taken from data on another site, where these calculations are routinely done. I haven't fully verified their accuracy - there may be some error in the last few digits. Fortunately, I won't be using that much precision anyway.

Answer 1

I don't know of a builtin .Net way to do it. I wrote this brute-force converter, but your values don't seem to exactly match up with .Net type precision - [double] (64bit) is too low precision, and [decimal] (128bit) is more.
Your examples come out like so:
0.0858b9da24fb4cac = 0.032603851087498366
= 0.0326038510874983682928164128
0.8c3115559ab0c10b = 0.5476239522928976
= 0.5476239522928976344718082711
Code:
<#
.Synopsis
Converts strings containing hexadecimal numbers with fractional components
into base-10 [decimal] numbers.
.EXAMPLE
PS C:\> ConvertFrom-HexFraction '0.0858b9da24fb4cac'
0.0326038510874983682928164128
.Example
PS C:\> '0.0858b9da24fb4cac', '0.8c3115559ab0c10b' | ConvertFrom-HexFraction
0.0326038510874983682928164128
0.5476239522928976344718082711
#>
function ConvertFrom-HexFraction
{
[CmdletBinding()]
[OutputType([decimal])]
Param
(
[Parameter(Mandatory=$true,
ValueFromPipeline=$true)]
[string]$hexValue
)
Process
{
# strip leading hex indicator, setup result placeholder of desired type.
$hexValue = $hexValue -replace '^(0x|&h)'
$result = [decimal]0
# Loop over the digits (hexits?) in the string, skip the (hexa)decimal point '.'
# and calculate (value * base ^ columnNum) for each.
$i = $hexValue.IndexOf('.') - 1
[char[]]$hexValue | Where { $_ -ne '.' } | ForEach {
$result += [convert]::ToInt32($_, 16) * [Math]::Pow(16, $i--)
}
$result #output the result
}
}
ConvertFrom-HexFraction '0.0'
ConvertFrom-HexFraction 'a.a'
ConvertFrom-HexFraction '0.0858b9da24fb4cac'
ConvertFrom-HexFraction '0.8c3115559ab0c10b'
'0.0858b9da24fb4cac', '0.8c3115559ab0c10b' | ConvertFrom-HexFraction

Answer 2

Ok, this one caught my interest. I didn't even know that hexadecimal fractions were a thing, so I went and looked it up. Converting them isn't covered in the [math] or [convert] libraries that I can see, so we'll have to write up a function that takes care of it for us. I wrote this up, and it's relatively accurate, but you have to consider that a fraction as small as you have it there's going to be some rounding... I mean really, for your first example even you rounded. The last digit alone is something like 6.50521303491303E-19 (which is 12*(16^-16)).
So, that function looks like:
Function HexToInt([string]$TextIn){
$Pre,$Post = $TextIn.split('.')
$PostConverted = For($i=1;$i -le $Post.Length;$i++){
[convert]::ToInt32($Post[($i-1)],16) * [math]::pow(16,($i*-1))
}
$PostSum = $PostConverted | Measure-Object -Sum |% Sum
$Int = [convert]::ToInt64($Pre,16)
$Int+$PostSum
}
That should convert your fractions for you.