Convert ByteArray to integer and real values

Question

during the import of a complex file format I handle ByteArray or lists of byte values. While I can easy transform them from one type to each other:

ba=ByteArray[{1,2,3,4,5,6}];
Normal[ba]

I have problems taking specific bytes of my list and converting them according a given number format e.g. Integer8, Integer32 or Real32.

Normal@ba[[1;;2]] (*Shall interpretet as Integer16*)
Normal@ba[[3;;6]] (*Shall interpretet as Real32*)

Is there an internal and elegant way to do so?

I wrote a workaround for Integer numbers like below but I would guess an internal solution will be way more efficient ...

ByteToInteger[byteArray_,LSBStart_:True,bitSize_:16,signed_:False] :=
    Module[{i,array=byteArray,value=0}, 

        (*Reverse for LSB*)
        If[LSBStart==False,
           array=Reverse[array];
        ];
        
        array=PadLeft[array,bitSize]

        
        (*calculate Unsigned value*)
        value=array[[1]];
        For[i=2,i<=Length@array,i++,
            value=value+array[[i]]*256^(i-1)
        ];
        
        (*adapt to signed if needed*)
        If[signed==True&&value>=2^(bitSize-1),
            value=-(2^bitSize-(value-2^(bitSize-1)))
        ];
        
        value  
    ]

I am open to any suggestions ...

Answer 1

ImportByteArray does what you need:

ba = ByteArray[{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12}];

ImportByteArray[ba[[1 ;; 4]], "Integer32"]
(*    {67305985}    *)

ImportByteArray[ba[[5 ;; 12]], "UnsignedInteger64"]
(*    {867798387104613893}    *)

Here's a list of availably types for import:

• "Bit" — individual binary bits (Import, Export only)
• "Byte" — 8-bit unsigned integer
• "Integer8", "Integer16", ... — 8-, 16-, 24- 32-, 64-, 128-bit signed integers
• "UnsignedInteger8", ... — 8-, 16-, 24-, 32-, 64-, 128-bit unsigned integers
• "Real32", "Real64", "Real128" — IEEE single‐, double‐, quad-precision real numbers
• "Complex64", "Complex128", "Complex256" — IEEE complex numbers
• "Character8", "Character16" — 8- and 16-bit (Unicode) characters
• "TerminatedString" — null-terminated string