endianstream.nim

import endians

proc swapEndian16*(outp, inp: pointer) = 
  ## copies `inp` to `outp` swapping bytes. Both buffers are supposed to
  ## contain at least 2 bytes.
  var i = cast[cstring](inp)
  var o = cast[cstring](outp)
  o[0] = i[1]
  o[1] = i[0]
when cpuEndian == bigEndian:
  proc bigEndian16(outp, inp: pointer) {.inline.} = copyMem(outp, inp, 2)
else:
  proc bigEndian16*(outp, inp: pointer) {.inline.} = swapEndian16(outp, inp)

proc readBE*[T: int16|uint16](src: var string; pos: var int; outp: var T) =
  bigEndian16(addr outp, addr src[pos])
  inc pos, 2
proc readBE*[T: float32|int32|uint32](src: var string; pos: var int; outp: var T) =
  bigEndian32(addr outp, addr src[pos])
  inc pos, 4
proc readBE*[T: float64|int64|uint64](src: var string; pos: var int; outp: var T) =
  bigEndian64(addr outp, addr src[pos])
  inc pos, 8

proc writeBE*[T: int16|uint16](dest: var string; pos: var int; val: var T) =
  bigEndian16(addr dest[pos], addr val)
  inc pos, 2
proc writeBE*[T: int32|uint32|float32](dest: var string; pos: var int; val: var T) =
  bigEndian32(addr dest[pos], addr val)
  inc pos, 4
proc writeBE*[T: int64|uint64|float64](dest: var string; pos: var int; val: var T) =
  bigEndian64(addr dest[pos], addr val)
  inc pos, 8

proc readInt16(src: var string; pos: var int): int16 =
  readBE src, pos, result
proc readInt32(src: var string; pos: var int): int32 =
  readBE src, pos, result
proc readInt64(src: var string; pos: var int): int64 =
  readBE src, pos, result

when isMainModule: 
  var 
    s2 = ""
    ani16 = 9001'u16
    ani32 = low(int32)
    ani64 = high(int64)-1
    i = 0
  template dumpvars() = echo ani32, " ", ani16, " ", ani64
  s2.setlen 50
  writeBE s2, i, ani32
  writeBE s2, i, ani16
  writeBE s2, i, ani64
  s2.setlen i
  dumpvars()
  echo(repr(s2), " ", len(s2))
  
  ani16 = 0
  ani32 = 0
  ani64 = 0
  i = 0
  readBE s2, i, ani32
  readBE s2, i, ani16
  readBE s2, i, ani64
  dumpvars()