module NHC.Binary
  ( getBitsF
  ) where

import NHC.GreenCard
import BinPtr    ({-type-}BinPtr(..))
import BinHandle ({-type-}BinHandle(..))

%-#include "cLowBinary.h"
%-#include <stdlib.h>
%-#include <stdio.h>

getBitsF :: BinHandle -> Int -> BinPtr -> (Int, BinPtr)
getBitsF bh w p = (getBitsFAux bh w p, toEnum (w + fromEnum p))

%fun getBitsFAux :: BinHandle -> Int -> BinPtr -> Int
%call (binHandle bh) (int width) (binPtr p)
%code
%  if (bh->mode != RO) {
%    fprintf(stderr,"Binary.getBitsF: BinHandle is not read-only.");
%    exit(1);
%  }
%  bh->cptr = p - forceCacheTo(bh,p)*8;
%  value = 0;
%  while (width > 0) {
%    int byte  = bh->cptr / 8;
%    int avail = 8 - (bh->cptr % 8);
%    if (width >= avail) {
%      value = (value<<avail)
%            | rhs(avail,bh->cache[byte]);
%      bh->cptr += avail;
%      width    -= avail;
%      if ((byte+1) == CACHESIZE) nextcache(bh);
%    } else {
%      value = (value<<width)
%            | (rhs(avail,bh->cache[byte]) >> (avail-width));
%      bh->cptr += width;
%      width     = 0;
%    }
%  }
%result (declare "unsigned" value in (int value))