Add parseUInt and parseBiggestUInt functions to stdlib (parseutils, strutils)

lib/pure/parseutils.nim

@@ -234,6 +234,57 @@ proc parseInt*(s: string, number: var int, start = 0): int {.
   elif result != 0:
     number = int(res)
 
+# overflowChecks doesn't work with uint64
+proc rawParseUInt(s: string, b: var uint64, start = 0): int =
+  var
+    res = 0'u64
+    prev = 0'u64
+    i = start
+  if s[i] == '+': inc(i) # Allow 
+  if s[i] in {'0'..'9'}:
+    b = 0
+    while s[i] in {'0'..'9'}:
+      prev = res
+      res = res * 10 + (ord(s[i]) - ord('0')).uint64
+      if prev > res:
+        return 0 # overflowChecks emulation
+      inc(i)
+      while s[i] == '_': inc(i) # underscores are allowed and ignored
+    b = res
+    result = i - start
+
+proc parseBiggestUInt*(s: string, number: var uint64, start = 0): int {.
+  rtl, extern: "npuParseBiggestUInt", noSideEffect.} =
+  ## parses an unsigned integer starting at `start` and stores the value into `number`.
+  ## Result is the number of processed chars or 0 if there is no integer or overflow detected.
+  var res: uint64
+  # use 'res' for exception safety (don't write to 'number' in case of an
+  # overflow exception):
+  result = rawParseUInt(s, res, start)
+  number = res
+
+# Workaround for high(uint)
+proc highUInt(): uint64 =
+  when sizeof(uint) == 4:
+    0xFFFFFFFF'u64
+  elif sizeof(uint) == 8:
+    0xFFFFFFFFFFFFFFFF'u64
+  else:
+    {.fatal: "Unknoun uint size: " & $sizeof(uint).}
+
+proc parseUInt*(s: string, number: var uint, start = 0): int {.
+  rtl, extern: "npuParseUInt", noSideEffect.} =
+  ## parses an unsigned integer starting at `start` and stores the value into `number`.
+  ## Result is the number of processed chars or 0 if there is no integer.
+  ## Result is the number of processed chars or 0 if there is no integer or overflow detected.
+  var res: uint64
+  result = parseBiggestUInt(s, res, start)
+  if (sizeof(uint) <= 4) and
+      (res > highUInt()):
+    raise newException(OverflowError, "overflow")
+  elif result != 0:
+    number = uint(res)
+
 proc parseBiggestFloat*(s: string, number: var BiggestFloat, start = 0): int {.
   magic: "ParseBiggestFloat", importc: "nimParseBiggestFloat", noSideEffect.}
   ## parses a float starting at `start` and stores the value into `number`.