Add basic data structure, initialization and endianess test

mpint.nimble

@@ -7,4 +7,17 @@ srcDir        = "src"
 
 ### Dependencies
 
-requires "nim >= 0.17.2"
+requires "nim >= 0.17.2"
+
+proc test(name: string, lang: string = "cpp") =
+  if not dirExists "build":
+    mkDir "build"
+  if not dirExists "nimcache":
+    mkDir "nimcache"
+  --run
+  --nimcache: "nimcache"
+  switch("out", ("./build/" & name))
+  setCommand lang, "tests/" & name & ".nim"
+
+task test, "Run all tests":
+  test "all_tests"

src/mpint.nim

@@ -0,0 +1,8 @@
+# Copyright (c) 2018 Status Research & Development GmbH
+# Distributed under the MIT License (license terms are at http://opensource.org/licenses/MIT).
+
+import  ./uint_type,
+        ./uint_init
+
+export  uint_type,
+        uint_init

src/private/utils.nim

@@ -0,0 +1,24 @@
+# Copyright (c) 2018 Status Research & Development GmbH
+# Distributed under the MIT License (license terms are at http://opensource.org/licenses/MIT).
+
+import ../uint_type
+
+proc bit_length*[T: BaseUint](n: T): int {.noSideEffect.}=
+  ## Calculates how many bits are necessary to represent the number
+  result = 1
+  var y: T = n shr 1
+  while y > 0.T:
+    y = y shr 1
+    inc(result)
+
+
+proc bit_length*[T: Natural](n: T): int {.noSideEffect.}=
+  ## Calculates how many bits are necessary to represent the number
+  #
+  # For some reason using "BaseUint or Natural" directly makes Nim compiler
+  # throw a type mismatch
+  result = 1
+  var y: T = n shr 1
+  while y > 0.T:
+    y = y shr 1
+    inc(result)

src/uint_init.nim

@@ -0,0 +1,29 @@
+# Copyright (c) 2018 Status Research & Development GmbH
+# Distributed under the MIT License (license terms are at http://opensource.org/licenses/MIT).
+
+import  typetraits
+
+import  private/utils,
+        uint_type
+
+proc initMpUint*[T: BaseUint; U: BaseUInt](n: T, base_type: typedesc[U]): MpUint[U] {.noSideEffect.} =
+  let len = n.bit_length
+  const sizeU_bits = sizeof(U) * 8
+
+  when not (T is type result):
+    if len >= 2 * sizeU_bits:
+      # Todo print n
+      raise newException(ValueError, "Input cannot be stored in a multi-precision integer of base " & $T.name &
+                                        "\nIt requires at least " & $len & " bits of precision")
+    elif len < sizeU_bits:
+      result.lo = n.U # TODO: converter for MpInts
+    else:
+      raise newException(ValueError, "Unsupported at the moment: are you trying to build MpUint[uint32] from an uint64?")
+  else:
+    n
+
+proc u128*[T: BaseUInt](n: T): UInt128 {.noSideEffect, inline.}=
+  initMpUint(n, uint64)
+
+proc u256*[T: BaseUInt](n: T): UInt256 {.noSideEffect, inline.}=
+  initMpUint(n, UInt256)

src/uint_type.nim

@@ -0,0 +1,16 @@
+# Copyright (c) 2018 Status Research & Development GmbH
+# Distributed under the MIT License (license terms are at http://opensource.org/licenses/MIT).
+
+
+type
+  MpUint*{.packed.}[BaseUint] = object
+    when system.cpuEndian == littleEndian:
+      lo*, hi*: BaseUint
+    else:
+      hi*, lo*: BaseUint
+
+  BaseUint* = SomeUnsignedInt or MpUint
+
+
+  UInt128* = MpUint[uint64]
+  UInt256* = MpUint[UInt128]

tests/all_tests.nim

@@ -0,0 +1,4 @@
+# Copyright (c) 2018 Status Research & Development GmbH
+# Distributed under the MIT License (license terms are at http://opensource.org/licenses/MIT).$
+
+import  test_endianness

tests/test_endianness.nim

@@ -0,0 +1,14 @@
+# Copyright (c) 2018 Status Research & Development GmbH
+# Distributed under the MIT License (license terms are at http://opensource.org/licenses/MIT).
+
+import ../src/mpint, unittest
+
+suite "Testing byte representation":
+  test "Byte representation conforms to the platform endianness":
+    let a = initMpUint(20182018, uint32)
+    let b = 20182018'u64
+
+    type AsBytes = array[8, byte]
+
+    check cast[AsBytes](a) == cast[AsBytes](b)
+