A very common issue we all face is comparing cases or scenarios of models we
run. It would be usefull to classify models based upon a set of
assumptions they may use. Yet storing each 100's of assumption values in
each case could be very daunting and consume huge amounts of space.

One solution is to create a range of input parameters that infrequently
change, then calculate a single hash value that represents the range.
When you run the model, you store the results, the frequently changing input
assumptions, and the hash value of the all the other assumptions.

You check the hash value against the database. If you find a match you know
you already stored all the infrequently changing assumption. If no match,
you stort the hash and all its corresponding inputs only once. Now with
the hash, it is easy to compare and contrast all the models with similar
sets of assumptions.

Question: Is there an easy way convert a range of cells into a Long
Integer hash value?

Stephen Bullen posted a very helpful hash algorithm that returns a hash that
is a 30 character string. (Thank you, Stephen!!!)
From: Stephen Bullen )
'Subject: Hash (MD5) in Excel
'Newsgroups: microsoft.public.Excel.programming Date: 2004-02-05
12:50:20 PST

I made a small change:
For Each oCell In rngData.Cells
If Not IsEmpty(oCell.Value) Then
vValue = oCell.Value
Else
'rasey 040608
vValue = oCell.Column * 256 + oCell.Row 'rasey
040608
End If
lResult = CryptHashData(hHash, VarPtr(vValue),
LenB(vValue), 0&)

Stephen skipped Empty cells, but I record a unique value for each empty cell
so that the position of assumption values is important to the hash instead
of simply the order of values.

While Stephen's original function returns a 30 character string, only the
first 16 are non-blank.

I am not after high security, just a simple quick index of assumptions of a
model run millions of times on a couple hundred assumptions. 16byte keys
are overkill for me.

Before I build by database using 16 byte string Primary Keys, I want to ask:
Is there an argument of CryptCreateHash or CryptGetHashParam that will
return a Long Integer instead of a string?

Thanks to all in advance.
And special thanks to Stephen Bullen for getting me 99.9% of the way.

Stephen Rasey
WiserWays
Houston, TX

For convenience, I am reposting Stephen Bullen's code from the 2004-02-05
post below:
Option Explicit



Declare Function CryptAcquireContext Lib "advapi32" Alias
"CryptAcquireContextA" (ByRef hProv As Long, ByVal sContainer As String, _

ByVal sProvider As String, ByVal lProvType As Long, ByVal lFlags As
Long) As Long



Declare Function CryptCreateHash Lib "advapi32" (ByVal hProv As Long, ByVal
lALG_ID As Long, _

ByVal hKey As Long, ByVal
lFlags As Long, ByRef hHash As Long) As Long



Declare Function CryptHashData Lib "advapi32" (ByVal hHash As Long, ByVal
lDataPtr As Long, ByVal lLen As Long, ByVal lFlags As Long) As

Long



Declare Function CryptGetHashParam Lib "advapi32" (ByVal hHash As Long,
ByVal lParam As Long, ByVal sBuffer As String, _

ByRef lLen As Long, ByVal
lFlags As Long) As Long



Declare Function CryptDestroyHash Lib "advapi32" (ByVal hHash As Long) As
Long



Declare Function CryptReleaseContext Lib "advapi32" (ByVal hProv As Long,
ByVal lFlags As Long) As Long



Const MS_DEF_PROV = "Microsoft Base Cryptographic Provider v1.0"

Const PROV_RSA_FULL As Long = 1

Const CRYPT_NEWKEYSET As Long = 8

Const CALG_MD5 As Long = 32771

Const HP_HASHVAL As Long = 2



Public Function GetMD5Hash(rngData As Range) As String



Dim hProv As Long

Dim hHash As Long

Dim lLen As Long

Dim oCell As Range

Dim baData() As Byte

Dim sBuffer As String

Dim vValue As Variant

Dim lResult As Long



'Get/create a cryptography context

CryptAcquireContext hProv, vbNullString, MS_DEF_PROV, PROV_RSA_FULL, 0

If hProv = 0 Then

CryptAcquireContext hProv, vbNullString, MS_DEF_PROV, PROV_RSA_FULL,
CRYPT_NEWKEYSET

End If



'If we got one...

If hProv < 0 Then



'Create an MD5 Hash

CryptCreateHash hProv, CALG_MD5, 0, 0, hHash



'If that was OK...

If hHash < 0 Then



'Fill it with the contents of the range

For Each oCell In rngData.Cells

If Not IsEmpty(oCell.Value) Then

vValue = oCell.Value

lResult = CryptHashData(hHash, VarPtr(vValue),
LenB(vValue), 0&)

End If

Next



'Create a buffer to store the hash value

sBuffer = Space(30)

lLen = 30



'Get the hash value

CryptGetHashParam hHash, HP_HASHVAL, sBuffer, lLen, 0



'Return the hash value

GetMD5Hash = Left$(sBuffer, lLen)



'Tidy up

CryptDestroyHash hHash

End If



'Tidy up

CryptReleaseContext hProv, 0

End If



End Function