# PsMWC32.ps1
# PowerShell script to generate psuedo random numbers using
# a 32-bit Multiply With Carry Generator.
#
# ----------------------------------------------------------------------
# Copyright (c) 2021 Richard L. Mueller
# Hilltop Lab web site - http://www.rlmueller.net
# Version 1.0 - December 6, 2021
#
# You have a royalty-free right to use, modify, reproduce, and
# distribute this script file in any way you find useful, provided that
# you agree that the copyright owner above has no warranty, obligations,
# or liability for such use.

Param (
    [Int32]$Count,
    [Int64]$Seed,
    [Int64]$Carry
)

Function Syntax ($ErrNum)
{
    # Subroutine to display error messages and syntax help.

    Switch ($ErrNum)
    {
        1 {Write-Host "Error, too many arguments." -ForegroundColor Red -backgroundColor Black}
        2 {Write-Host "Error, seed must be greater than or equal to 0." -ForegroundColor Red -backgroundColor Black}
        3 {Write-Host "Error, seed must be less than 2^32 (4,294,967,296)" -ForegroundColor Red -backgroundColor Black}
        4 {Write-Host "Error, count must be positive." -ForegroundColor Red -backgroundColor Black}
        5 {Write-Host "Error, carry must be greater than or equal to 0." -ForegroundColor Red -backgroundColor Black}
        6 {Write-Host "Error, carry must be less than 2^32 (4,294,967,296)." -ForegroundColor Red -backgroundColor Black}
        7 {Write-Host "Error, carry cannot be A - 1 = 4,164,903,689." -ForegroundColor Red -backgroundColor Black}
    }
    Write-Host "-----"
    Write-Host "PsMWC32.ps1 - PowerShell program to generate random numbers."
    Write-Host "Syntax:"
    Write-Host "    PowerShell .\PsMWC32.ps1 <count> <seed> <carry>"
    Write-Host "where:"
    Write-Host "    <count> is number of random integers to display (optional)."
    Write-Host "        Count must be a positive integer, with no commas."
    Write-Host "        Default value is 10."
    Write-Host "    <seed> is a seed value (optional)."
    Write-Host "        Seed must be an integer greater than or equal to 0"
    Write-Host "        and less than 2^32 (no commas). Default value is based"
    Write-Host "        on the system timer."
    Write-Host "    <carry> a carry value (optional)."
    Write-Host "        Carry must be an integer greater than or equal to 0"
    Write-Host "        and less than 2^32 (no commas). Default value is 2,634,046,488"
    Write-Host "Program outputs psuedo random integers greater than or equal"
    Write-Host "to 0 and less than 2^32 (4,294,967,296)."
    Write-Host "Copyright(c) 2021 Richard L. Mueller"
    Write-Host "Version 1.0 - December 6, 2021"

    Return $True
}

# Use default if parmeter not specified.
# Default count is 10.
If ($Count -eq 0) {$Count = 10}
# Default Seed is based on the system time since midnight in seconds.
If ($Seed -eq 0)
{
    $D1 = [Int16](Get-Date -Format HH)
    $D2 = [Int16](Get-Date -Format mm)
    $D3 = [Int16](Get-Date -Format ss)
    $D4 = $D3 + (60 * ($D2 + (60 * $D1)))
    $D5 = $D4 * 4294967296
    $Seed = [System.Math]::Truncate($D5 / (24 * 60 * 60))
}
# The default initial carry is based on the system date and time.
If ($Carry -eq 0)
{
    $D1 = [Int16](Get-Date -Format MM)
    $D2 = [Int16](Get-Date -Format dd)
    $D3 = [Int16](Get-Date -Format yy)
    $D4 = [Int16](Get-Date -Format HH)
    $D5 = [Int16](Get-Date -Format mm)
    $D6 = [Int16](Get-Date -Format ss)
    $D7 = ($D6 + (60 * $D5) + (3600 * $D4)) / (24 * 3600)
    $D8 = $D2 + ($D1 * 30) + ($D3 * 365) + 36505
    $D9 = [System.Math]::Truncate(($D7 + $D8) * 100000000000)
    $D10 = [System.Math]::Truncate($D9 / 4294967296)
    $Carry = $D9 - (4294967296 * $D10)
}

# Validate arguments.
If ($Args.Count -gt 0) {If (Syntax 1) {Exit}}
If ($Seed -lt 0) {If (Syntax 2) {Exit}}
If (($Seed - 4294967296) -gt 0) {If (Syntax 3) {Exit}}
If ($Count -lt 0) {If (Syntax 4) {Exit}}
If ($Carry -lt 0) {If (Syntax 5) {Exit}}
If (($Carry - 4294967296) -gt 0) {If (Syntax 6) {Exit}}
# Carry cannot be 0 or A - 1 = 4,164,903,689.
If ($Carry -eq 4164903689) {If (Syntax 7) {Exit}}

# Output the initial seed and carry values.
"Initial Seed = " + '{0:n0}' -f $Seed + "  Initial Carry = " + '{0:n0}' -f $Carry

# Display number of integers requested from the psuedo random number generator.
"$Count psuedo random integers:"
" "

Function MWC ([Int64]$X, [Int64]$C)
{
    # Constants.
    # $A = 4,164,903,690
    # $M = 4,294,967,296
    # $H = 65,536
    $A_hi = 63551
    $A_lo = 25354
    [Int64]$M = 4294967296
    $H = 65536

    $X_hi = [System.Math]::Truncate($X / $H)
    $X_lo = $X - ($X_hi * $H)
    $C_hi = [System.Math]::Truncate($C / $H)
    $C_lo = $C - ($C_hi * $H)
    # $A = (($A_hi * $H) + $A_lo)
    # $X = (($X_hi * $H) + $X_lo)
    # $C = (($C_hi * $H) + $C_lo)

    [Int64]$F1 = $A_hi * $X_hi
    [Int64]$F2 = ($A_hi * $X_lo) + ($A_lo * $X_hi) + $C_hi
    [Int64]$F3 = ($A_lo * $X_lo) + $C_lo

    [Int64]$T1 = [System.Math]::Truncate($F2 / $H)
    [Int64]$T2 = $M * $T1

    [Int64]$Xn = ((($F2 * $H) % $M) + $F3) % $M
    [Int64]$Cn = [System.Math]::Truncate(($F2 / $H) + $F1)

    Return @($Xn, $Cn)
}

For ($k = 1;$k -le $Count;$k = $k + 1)
{
    [Int64]$M = 4294967296
    $New = MWC $Seed $Carry
    $Seed = $New[0]
    $Carry = $New[1]

    # Output seed from this iteration.
    '{0:n0}' -f $Seed
    # Alternate output statement for research.
    # " $k : Seed = " + '{0:n0}' -f $Seed + ", Carry = " + '{0:n0}' -f $Carry
    # Alternate output statement for normalized real numbers, greater or equal to 0 and less than 1.
    # '{0:n15}' -f ($Seed / $M)

}