(* readbmp reads a BMP bitmap file *)
fun get2(s,i)=ordof(s,i)+256*ordof(s,i+1);
fun get4(s,i)=get2(s,i)+256*256*get2(s,i+2);
fun pad4 x = ~4*(~x div 4)
fun ttt 0= 1|ttt 1= 2|ttt 2=  4|ttt 3=8|ttt 4=16
|   ttt 5=32|ttt 6=64|ttt 7=128|ttt 8=256;
fun bits(b,s,n)=chr((ord b div ttt(s*n)) mod (ttt n))
fun readbmp s = let
        val fh = open_in s
        val header = input(fh,54)
        val bitspp = get2(header,28)
        val colTab = input(fh,get4(header,10) - 54)
        val bitMap = input(fh,get4(header,34))
        val w = get4(header,18)
        val h = get4(header,22)
        val dy = pad4((bitspp * w) div 8)
	fun outrange(x,y)=x<0 orelse y<0 orelse x>=w orelse y>=h
	val r = 8 div bitspp
	fun col(x,y) = if outrange(x,y) then "\000" else
		bits(substring(bitMap,dy*y+(x div r),1),r-1-(x mod r),bitspp)
        in (w,h,colTab,col) end;