AK: Add convert_to_uint_from_octal

Author: https://github.com/xavier
Commit: https://github.com/SerenityOS/serenity/commit/9e97823ff8b
Pull-request: https://github.com/SerenityOS/serenity/pull/11319
Reviewed-by: https://github.com/bgianfo

AK/StringUtils.cpp

@@ -191,6 +191,41 @@ template Optional<u16> convert_to_uint_from_hex(StringView str, TrimWhitespace);
 template Optional<u32> convert_to_uint_from_hex(StringView str, TrimWhitespace);
 template Optional<u64> convert_to_uint_from_hex(StringView str, TrimWhitespace);
 
+template<typename T>
+Optional<T> convert_to_uint_from_octal(StringView str, TrimWhitespace trim_whitespace)
+{
+    auto string = trim_whitespace == TrimWhitespace::Yes
+        ? str.trim_whitespace()
+        : str;
+    if (string.is_empty())
+        return {};
+
+    T value = 0;
+    const auto count = string.length();
+    const T upper_bound = NumericLimits<T>::max();
+
+    for (size_t i = 0; i < count; i++) {
+        char digit = string[i];
+        u8 digit_val;
+        if (value > (upper_bound >> 3))
+            return {};
+
+        if (digit >= '0' && digit <= '7') {
+            digit_val = digit - '0';
+        } else {
+            return {};
+        }
+
+        value = (value << 3) + digit_val;
+    }
+    return value;
+}
+
+template Optional<u8> convert_to_uint_from_octal(StringView str, TrimWhitespace);
+template Optional<u16> convert_to_uint_from_octal(StringView str, TrimWhitespace);
+template Optional<u32> convert_to_uint_from_octal(StringView str, TrimWhitespace);
+template Optional<u64> convert_to_uint_from_octal(StringView str, TrimWhitespace);
+
 bool equals_ignoring_case(StringView a, StringView b)
 {
     if (a.length() != b.length())

AK/StringUtils.h

@@ -56,6 +56,8 @@ template<typename T = unsigned>
 Optional<T> convert_to_uint(StringView, TrimWhitespace = TrimWhitespace::Yes);
 template<typename T = unsigned>
 Optional<T> convert_to_uint_from_hex(StringView, TrimWhitespace = TrimWhitespace::Yes);
+template<typename T = unsigned>
+Optional<T> convert_to_uint_from_octal(StringView, TrimWhitespace = TrimWhitespace::Yes);
 bool equals_ignoring_case(StringView, StringView);
 bool ends_with(StringView a, StringView b, CaseSensitivity);
 bool starts_with(StringView, StringView, CaseSensitivity);

Tests/AK/TestStringUtils.cpp

@@ -226,6 +226,60 @@ TEST_CASE(convert_to_uint)
     EXPECT(!actual_u64.has_value());
 }
 
+TEST_CASE(convert_to_uint_from_octal)
+{
+    auto value = AK::StringUtils::convert_to_uint_from_octal<u16>(StringView());
+    EXPECT(!value.has_value());
+
+    value = AK::StringUtils::convert_to_uint_from_octal<u16>("");
+    EXPECT(!value.has_value());
+
+    value = AK::StringUtils::convert_to_uint_from_octal<u16>("a");
+    EXPECT(!value.has_value());
+
+    value = AK::StringUtils::convert_to_uint_from_octal<u16>("+");
+    EXPECT(!value.has_value());
+
+    value = AK::StringUtils::convert_to_uint_from_octal<u16>("-");
+    EXPECT(!value.has_value());
+
+    value = AK::StringUtils::convert_to_uint_from_octal<u16>("+1");
+    EXPECT(!value.has_value());
+
+    value = AK::StringUtils::convert_to_uint_from_octal<u16>("-1");
+    EXPECT(!value.has_value());
+
+    value = AK::StringUtils::convert_to_uint_from_octal<u16>("8");
+    EXPECT(!value.has_value());
+
+    auto actual = AK::StringUtils::convert_to_uint_from_octal<u16>("77777777");
+    EXPECT(!actual.has_value());
+
+    actual = AK::StringUtils::convert_to_uint_from_octal<u16>("0");
+    EXPECT_EQ(actual.has_value(), true);
+    EXPECT_EQ(actual.value(), 0u);
+
+    actual = AK::StringUtils::convert_to_uint_from_octal<u16>("1");
+    EXPECT_EQ(actual.has_value(), true);
+    EXPECT_EQ(actual.value(), 1u);
+
+    actual = AK::StringUtils::convert_to_uint_from_octal<u16>("0755");
+    EXPECT_EQ(actual.has_value(), true);
+    EXPECT_EQ(actual.value(), 0755u);
+
+    actual = AK::StringUtils::convert_to_uint_from_octal<u16>("755");
+    EXPECT_EQ(actual.has_value(), true);
+    EXPECT_EQ(actual.value(), 0755u);
+
+    actual = AK::StringUtils::convert_to_uint_from_octal<u16>(" \t644 \n\n");
+    EXPECT_EQ(actual.has_value(), true);
+    EXPECT_EQ(actual.value(), 0644u);
+
+    actual = AK::StringUtils::convert_to_uint_from_octal<u16>("177777");
+    EXPECT_EQ(actual.has_value(), true);
+    EXPECT_EQ(actual.value(), 0177777u);
+}
+
 TEST_CASE(ends_with)
 {
     String test_string = "ABCDEF";