Where would we be without people like you on this list! Many thanks Rob. It works!
Regards, Ross. -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Rob Kennedy Sent: Monday, 14 January 2008 6:55 a.m. To: Borland's Delphi Discussion List Subject: Re: non-standard bit numbers Ross Levis wrote: > I hope someone can help me!! I need to read the header of a binary audio > file (FLAC) which uses non-standard portions of bits for numeric fields. It > also uses Big Endian. I have a function to convert normal 16 & 32 bit > integers from little to big endian, but bit divisions in numbers is beyond > me. > > Here is the structure in bits. > > <20> SampleRate > <3> Channels > <5> BitsPerSample > <36> TotalSamples > > This adds up to 64 bits (8 bytes). Given an array [1..8] of byte, can > someone please help me obtain the value of these 4 fields. The layout of your array is like this: ssssssss ssssssss sssscccb bbbbtttt tttttttt tttttttt tttttttt tttttttt Put a comment like that in your source code and refer to it. SampleRate is 20 bits. Divided by eight bits per byte gives two full bytes plus half the next. SampleRate := (Data[1] shl 12) // make room for Data[2..3] or (Data[2] shl 4) // make room for Data[3] or (Data[3] shr 4); // eliminate cccb That grabs the upper four bits of Data[3] and shifts them into the first four positions, which are where they need to be in SampleRate. Doing that implicitly throws away the first four bits. Channels := (Data[3] shr 1) // eliminate b and $7; // select only the first three bits. // $7 = (2^3) - 1 BitsPerSample := ((Data[3] and $1) // select only the first bit shl 4) // make room for Data[4] or (Data[4] shr 4); // eliminate tttt TotalSamples := (Int64(Data[4] and $f) // select the first four bits // $f = (2^4) - 1 shl 32) // make room for Data[5..8] or (Data[5] shl 24) // make room for Data[6..8] or (Data[6] shl 16) // make room for Data[7..8] or (Data[7] shl 8) // make room for Data[8] or Data[8]; TotalSamples needs to be an Int64, but the rest can all be Integer. -- Rob _______________________________________________ Delphi mailing list -> [email protected] http://lists.elists.org/cgi-bin/mailman/listinfo/delphi
