ElfHash c translation

[Brad McLane]

I am struggling with the translation of the ElfHash() function from c to PB.

Here's the c code:

unsigned long ElfHash(const unsigned char *key)
{
  unsigned long h = 0;
  while (*key) {
    h = (h << 4) + *key++;
    unsigned long g = h & 0xF0000000L;
    if (g) h ^= g >> 24;
    h &= ~g;
  }
  return h;
}

Now I know why I've always found excuses not to code in c: Too many cryptic operators!

Here's my best hack at a PB translation:

Function ElfHash(sKey As String) As Long
Local h As Long
Local g As Long
Local i As Long
Local b As Byte
Local lpsKey As Long
Local lLen As Long
h = 0


lpsKey = StrPtr(sKey)


For i = 0 To Len(sKey)
  Shift Left h, 4
  Incr lpsKey
  b = Peek(lpsKey)
  h = h + b
  g = h And &HF0000000&
  If IsTrue(g) Then
     Shift Right g, 24
     h = h Xor g
  End If
  h = h And -g

Next

Function = h

End Function

Function PbMain()

     Print Str$(ElfHash("test"))

End Function

The PB code runs but it always returns zero.

Anyone have any suggestions?


Brad



------------------

[Dave Navarro]

Originally posted by Brad McLane:

unsigned long ElfHash(const unsigned char *key)
{
  unsigned long h = 0;
  while (*key) {
    h = (h << 4) + *key++;
    unsigned long g = h & 0xF0000000L;
    if (g) h ^= g >> 24;
    h &= ~g;
  }
  return h;
}

Here's my translation...

FUNCTION ElfHash(sKey AS STRING) AS LONG
 
  LOCAL key AS BYTE PTR
  LOCAL h AS DWORD
  LOCAL g AS DWORD
 
  key = STRPTR(sKey)
 
  h = 0
  WHILE @key
    SHIFT LEFT h, 4
    h = h + @key
    key = key + 1
    g = h AND &HF0000000???
    IF g THEN
      SHIFT RIGHT g, 24
      h = h XOR g  'h ^= g
    END IF
    h = h AND (NOT g)  'h &= ~g;
  WEND
 
  FUNCTION = h
 
END FUNCTION

--Dave

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[Brad McLane]

That one works much better.

Thanks Dave!

------------------

[Wayne Diamond]

Dave,
Your port produces incorrect results, and unfortunately it has gone unnoticed for one and a half years
But better late than never! Here's a fixed one:

FUNCTION Elf32(sKey AS STRING) AS LONG
  LOCAL key AS BYTE PTR
  LOCAL h AS LONG
  LOCAL g AS LONG
  LOCAL i AS LONG
  key = STRPTR(sKey)
  h = 0
  WHILE @key
    SHIFT LEFT h, 4
    h = h + @key
    key = key + 1
    g = h AND &HF0000000???
    IF g THEN
      i = g
      SHIFT RIGHT i, 24
      h = h XOR i
    END IF
    h = h AND (NOT g)
  WEND
  FUNCTION = h
END FUNCTION

And here's my inline port:

FUNCTION Elf32(sKey AS STRING) AS DWORD
#REGISTER NONE
LOCAL lLen AS DWORD, ptrStr AS DWORD, H AS DWORD
lLen = LEN(sKey)
ptrStr = STRPTR(sKey)
       ! xor ebx, ebx      ; ebx = result holder (H)
       ! mov edx, lLen     ; edx = Length
       ! mov ecx, ptrStr   ; ecx = Ptr to string
       ! xor esi, esi
    Elf1:
       ! xor eax, eax
       ! shl ebx, 4
       ! mov al, [ecx]
       ! add ebx, eax
       ! inc ecx
       ! mov eax, ebx
       ! and eax, &HF0000000???
       ! cmp eax, 0
       ! je Elf2
       ! mov esi, eax
       ! shr esi,24
       ! xor ebx, esi
    Elf2:
       ! not eax
       ! and ebx,eax
       ! dec edx
       ! cmp edx, 0
       ! jne Elf1
       ! mov H,ebx
    FUNCTION = H
END FUNCTION

See also http://www.wanet.com.au/~diamond/pbc...lgorithm=elf32


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The PowerBASIC Crypto Archives

[This message has been edited by Wayne Diamond (edited July 24, 2002).]