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Task/Variable-length-quantity/Nim/variable-length-quantity.nim

@@ -0,0 +1,24 @@
+import unsigned, strutils
+
+proc toSeq(x: uint64): seq[uint8] =
+  var x = x
+  result = @[]
+  var f = 0
+  for i in countdown(9, 1):
+    if (x and (127'u64 shl uint((i * 7)))) > 0'u64:
+      f = i
+      break
+  for j in 0..f:
+    result.add(uint8((x shr uint64((f - j) * 7)) and 127) or 128)
+
+  result[f] = result[f] xor 128'u8
+
+proc fromSeq(xs): uint64 =
+  result = 0
+  for x in xs:
+    result = (result shl 7) or (x and 127)
+
+for x in [0x7f'u64, 0x4000'u64, 0'u64, 0x3ffffe'u64, 0x1fffff'u64,
+          0x200000'u64, 0x3311a1234df31413'u64]:
+  let c = toSeq(x)
+  echo "seq from $#: $# back: $#".format(x, c, fromSeq(c))