zcat vs CamlZip

[Sam Steingold <sds@podval.org>]

I read through a huge *.gz file.
I have two versions of the code:

1. use Unix.open_process_in "zcat foo.gz".

2. use gzip.mli (1.2 2002/02/18) as comes with godi 3.09.

it turns out that the zcat version is 3(!) times as fast as the gzip.mli 
one:

Run time: 189.435840 sec
Self:     189.435840 sec
      sys: 183.447465 sec
     user: 5.988375 sec
Children: 0.000000 sec
      sys: 0.000000 sec
     user: 0.000000 sec
GC:     minor: 169778
         major: 478
   compactions: 3
Allocated:  5510457762.0 words
Wall clock:  206 sec (00:03:26)

vs

Run time: 58.471655 sec
Self:     54.855429 sec
      sys: 48.527033 sec
     user: 6.328396 sec
Children: 3.616226 sec
      sys: 3.168198 sec
     user: 0.448028 sec
GC:     minor: 43174
         major: 229
   compactions: 5
Allocated:  1401290543.0 words
Wall clock:  78 sec (00:01:18)

since gzip.mli lacks input_line function, I had to roll my own:

let buf = Buffer.create 1024
let gz_input_line gz_in char_counter line_counter =
   Buffer.clear buf;
   let finish () = incr line_counter; Buffer.contents buf in
   let rec loop () =
     let ch = Gzip.input_char gz_in in
     char_counter := Int64.succ !char_counter;
     if ch = '\n' then finish () else ( Buffer.add_char buf ch; loop (); 
) in
   try loop ()
   with End_of_file ->
     if Buffer.length buf = 0 then raise End_of_file else finish ()

is there something wrong with my gz_input_line?
is this a know performance issue with the CamlZip library?

thanks.
Sam.