switch to fixed-width storage for word list

passphrase.nimble

@@ -33,6 +33,13 @@ task(dictionary, "Generate dictionary from BNC XML files"):
   echo output.strip().splitlines()[^1]
 
 
+task(pack, "Pack dictionary into fixed-width file and compress"):
+  echo "Packing dictionary"
+  echo runCmd("nim c --run src/dictionary.nim data/dictionary.txt data/dictionary.pack")
+
+
 before(build):
   if not fileExists("data/dictionary.txt"):
     dictionaryTask()
+  if not fileExists("data/dictionary.pack"):
+    packTask()

src/dictionary.nim

@@ -5,82 +5,58 @@ import zippy
 type
   Dictionary* = object
     words: string
-    offsets: seq[uint32]
+    width: uint32
 
 
 proc `[]`*(d: Dictionary, i: Natural): string =
-  # last word has no following start index, so we have to fake it
-  # also strings are indexed with ints
-  let slice = 
-    if i == d.offsets.high:
-      d.offsets[i].int .. d.words.high
-    else:
-      d.offsets[i].int ..< d.offsets[i + 1].int
-
-  result = d.words[slice]
+  let start = i.uint32 * d.width
+  d.words[start ..< start + d.width]
 
 
 proc len*(d: Dictionary): int =
-  result = d.offsets.len
+  result = d.words.len div d.width.int
 
 
-proc addU32(s: var seq[uint8], i: uint32) =
+proc addU32(s: var string, i: uint32) =
   for offset in 0..3:
-    let b = cast[uint8](i shr (offset * 8))
+    let b = cast[char](i shr (offset * 8))
     s.add(b)
 
 
-proc getU32(s: seq[uint8]): uint32 =
+proc getU32(s: string): uint32 =
   for offset in 0..3:
     result = result or (cast[uint32](s[offset]) shl (offset * 8))
 
 
-proc pack*(d: Dictionary): seq[uint8] =
-  let compressed = cast[seq[uint8]](d.words)
-  let lenWords = compressed.len
-  let lenOffsets = d.offsets.len * 4
-  # 8 extra bytes for the length specifiers
-  var buff = newSeqOfCap[uint8](lenWords + lenOffsets + 8)
-  buff.addU32(lenWords.uint32)
-  buff.add(compressed)
-  buff.addU32(lenOffsets.uint32)
-  for offset in d.offsets:
-    buff.addU32(offset)
-  result = buff.compress(dataFormat = dfGzip)
+proc pack*(d: Dictionary): string =
+  var data: string
+  data.addU32(d.width)
+  data.add(d.words)
+  data.compress(dataFormat = dfGzip)
 
 
-proc unpack*[T: seq[uint8]|string](p: T): Dictionary =
-  when T is string:
-    let buff = cast[seq[uint8]](p.uncompress(dataFormat = dfGzip))
-  else:
-    let buff = p.uncompress(dataFormat = dfGzip)
-  
-  let lenWords = buff.getU32()
-  let nextSection = lenWords + 4
-  let words = cast[string](buff[4 ..< nextSection])
-
-  let numOffsets = buff[nextSection ..< (nextSection + 4)].getU32() div 4
-  var offsets = newSeqOfCap[uint32](numOffsets)
-  for i in 0 ..< numOffsets:
-    let idx = nextSection + 4 + (i * 4)
-    let offset = buff[idx ..< idx + 4].getU32()
-    offsets.add(offset)
-
-  result = Dictionary(words: words, offsets: offsets)
+proc unpack*(p: string): Dictionary =
+  let data = p.uncompress(dataFormat = dfGzip)
+  result.width = data.getU32()
+  result.words = data[4..^1]
 
 
-proc loadWords*(): Dictionary =
-  var i: uint32
-  for word in readFile("../data/dictionary.txt").strip().splitLines():
+proc loadWords*(path: string): Dictionary =
+  result.width = 25
+  for word in readFile(path).strip().splitLines():
+    if word.len > 25:
+      continue
+
     result.words.add(word)
-    result.offsets.add(i)
-    i += word.len.uint32
+    for _ in 0..<(25 - word.len):
+      result.words.add(' ')
 
 
 when isMainModule:
+  import std/os
   echo "Loading words..."
-  let dictionary = loadWords()
+  let dictionary = loadWords(paramStr(1))
   echo "Packing dictionary..."
   let packed = dictionary.pack()
-  discard open("../data/dictionary.pack", fmWrite).writeBytes(packed, 0, packed.len)
+  writeFile(paramStr(2), packed)
   echo "Dictionary packed."

src/passphrase.nim

@@ -13,7 +13,7 @@ proc genPassphrase(dict: Dictionary, length, dictSize: int): string =
   var words: seq[string]
   for r in rands:
     let i = r mod dictSize.uint64
-    words.add(dict[i])
+    words.add(dict[i].strip())
   result = words.join(" ")
 
 
@@ -52,6 +52,5 @@ proc parseInput(dictLen: int): (int, int) =
 
 when isMainModule:
   let dict = packed.unpack()
-  echo dict.len
   let (length, dictSize) = parseInput(dict.len)
   echo genPassphrase(dict, length, dictSize)