implement strtol clone for Erlang

erlang/apps/lib/src/strtol.erl

@@ -0,0 +1,121 @@
+%%% -*- erlang-indent-level: 2 -*-
+%%%
+%%% Copyright (C) 2018  Mikael Pettersson
+%%%
+%%% Licensed under the Apache License, Version 2.0 (the "License");
+%%% you may not use this file except in compliance with the License.
+%%% You may obtain a copy of the License at
+%%%
+%%%     http://www.apache.org/licenses/LICENSE-2.0
+%%%
+%%% Unless required by applicable law or agreed to in writing, software
+%%% distributed under the License is distributed on an "AS IS" BASIS,
+%%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+%%% See the License for the specific language governing permissions and
+%%% limitations under the License.
+%%%
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+%%%
+%%% Provides C strto[u]l(3) like functionality in Erlang.  Erlang's built-in
+%%% support (erlang:list_to_integer/[12], string:to_integer/1, and
+%%% io_lib:fread/[23]) is too Erlang-centric to be a drop-in replacement.
+%%% Since Erlang has bignums, this code performs no overflow checks.
+
+-module(strtol).
+-export([parse/2]).
+
+-type base() :: 0 | 2..36.
+
+-spec parse(string(), base()) -> {ok, integer(), string()} | {error, any()}.
+parse(String, Base) ->
+  scan_spaces(String, Base).
+
+scan_spaces(String, Base) ->
+  case String of
+    [C | Rest] ->
+      case isspace(C) of
+        true -> scan_spaces(Rest, Base);
+        false -> scan_sign(C, Rest, Base)
+      end;
+    [] -> no_digits()
+  end.
+
+scan_sign(C, Rest, Base) ->
+  case C of
+    $- -> scan_base(Rest, Base, _Minus = true);
+    $+ -> scan_base(Rest, Base, _Minus = false);
+    _  -> scan_base([C | Rest], Base, _Minus = false)
+  end.
+
+scan_base(String, Base, Minus) ->
+  case Base of
+    0 ->
+      case String of
+        [$0, C | Rest] when C =:= $x; C =:= $X ->
+          scan_digits(Rest, _Base = 16, Minus);
+        [$0 | Rest] ->
+          scan_digits(Rest, _Base = 8, Minus);
+        _ ->
+          scan_digits(String, _Base = 10, Minus)
+      end;
+    16 ->
+      case String of
+        [$0, C | Rest] when C =:= $x; C =:= $X ->
+          scan_digits(Rest, Base, Minus);
+        _ ->
+          scan_digits(String, Base, Minus)
+      end;
+    _ when Base >= 2, Base =< 36 ->
+      scan_digits(String, Base, Minus);
+    _ ->
+      invalid_base()
+  end.
+
+scan_digits(String, Base, Minus) ->
+  case String of
+    [C | Rest] ->
+      D = digit_value(C),
+      if D < Base -> scan_digits(Rest, D, Base, Minus);
+         true -> no_digits()
+      end;
+    [] -> no_digits()
+  end.
+
+scan_digits(String, Value, Base, Minus) ->
+  case String of
+    [C | Rest] ->
+      D = digit_value(C),
+      if D < Base -> scan_digits(Rest, Value * Base + D, Base, Minus);
+         true -> return(String, Value, Minus)
+      end;
+    [] ->
+      return([], Value, Minus)
+  end.
+
+return(Rest, Value0, Minus) ->
+  Value = if Minus -> -Value0; true -> Value0 end,
+  {ok, Value, Rest}.
+
+no_digits() ->
+  {error, no_digits}.
+
+invalid_base() ->
+  {error, invalid_base}.
+
+isspace(C) ->
+  case C of
+    $\s -> true;
+    $\f -> true;
+    $\n -> true;
+    $\r -> true;
+    $\t -> true;
+    $\v -> true;
+    _   -> false
+  end.
+
+digit_value(C) ->
+  if C >= $0, C =< $9 -> C - $0;
+     C >= $A, C =< $Z -> C - $A + 10;
+     C >= $a, C =< $z -> C - $a + 10;
+     true -> 255 % out-of-band value >= any valid base
+  end.