Cool, thanks for the info. So it seems as if there is no additional information in the encoding to say that it is a varint, just the raw bytes of it. I'll give it a shot.
-Jonathan On Monday, January 6, 2014 1:17:45 PM UTC-8, Ilia Mirkin wrote: > > On Mon, Jan 6, 2014 at 2:07 PM, <[email protected] <javascript:>> > wrote: > > Sorry if this has been covered before. I searched but couldn't find a > > complete answer (or at least what I thought was complete). > > > > When I write a varint to a coded output stream via > > coded_stream.WriteVarInt32([some value]) is it possible to just do a > quick > > calculation to find the number of bytes that would be written to the > stream > > in that scenario just based on the value of the integer passed in? > > > > Is there any additional overhead to indicate that it is a varint when > > encoded to the stream or is the varint size just the same calculation as > > dictated in the language docs (here > > > https://developers.google.com/protocol-buffers/docs/encoding?hl=zh-CN#varints). > > > > Obviously one easy way to find the size out be to create a coded output > > stream, write the varint to it and then find the byte size difference. > I'm > > just wondering if there is a better/faster way than having to construct > and > > delete a coded output stream for a calculation. > > Find the highest bit set on your integer, divide by 7 and round up > (i.e. + 6 / 7) -- that should be the number of bytes it takes to > encode the varint. On x86, there is a bsr instruction which computes > ilog2 (with gcc you could do e.g. 32 - __builtin_clz(var)). > > -ilia > -- You received this message because you are subscribed to the Google Groups "Protocol Buffers" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/protobuf. For more options, visit https://groups.google.com/groups/opt_out.
