kj/string: parse 0x prefixed integers in base 16, add documentation

c++/src/kj/string-test.c++

@@ -102,6 +102,13 @@ TEST(String, parseAs) {
   KJ_EXPECT_THROW_MESSAGE("not contain valid", StringPtr("a").parseAs<int64_t>());
   KJ_EXPECT_THROW_MESSAGE("not contain valid", StringPtr("1a").parseAs<int64_t>());
   KJ_EXPECT_THROW_MESSAGE("not contain valid", StringPtr("+-1").parseAs<int64_t>());
+  EXPECT_EQ(StringPtr("010").parseAs<int64_t>(), 10);
+  EXPECT_EQ(StringPtr("0010").parseAs<int64_t>(), 10);
+  EXPECT_EQ(StringPtr("0x10").parseAs<int64_t>(), 16);
+  EXPECT_EQ(StringPtr("0X10").parseAs<int64_t>(), 16);
+  EXPECT_EQ(StringPtr("-010").parseAs<int64_t>(), -10);
+  EXPECT_EQ(StringPtr("-0x10").parseAs<int64_t>(), -16);
+  EXPECT_EQ(StringPtr("-0X10").parseAs<int64_t>(), -16);
 
   EXPECT_EQ(StringPtr("1").parseAs<uint64_t>(), 1);
   EXPECT_EQ(StringPtr("0").parseAs<uint64_t>(), 0);

c++/src/kj/string.c++

@@ -34,12 +34,16 @@ namespace kj {
 #endif
 
 namespace {
+bool isHex(const char *s) {
+  if (*s == '-') s++;
+  return s[0] == '0' && (s[1] == 'x' || s[1] == 'X');
+}
 
 long long parseSigned(const StringPtr& s, long long min, long long max) {
   KJ_REQUIRE(s != nullptr, "String does not contain valid number", s);
   char *endPtr;
   errno = 0;
-  auto value = strtoll(s.begin(), &endPtr, 10);
+  auto value = strtoll(s.begin(), &endPtr, isHex(s.cStr()) ? 16 : 10);
   KJ_REQUIRE(endPtr == s.end(), "String does not contain valid number", s);
   KJ_REQUIRE(errno != ERANGE, "Value out-of-range", s);
   KJ_REQUIRE(value >= min && value <= max, "Value out-of-range", value, min, max);
@@ -50,7 +54,7 @@ unsigned long long parseUnsigned(const StringPtr& s, unsigned long long max) {
   KJ_REQUIRE(s != nullptr, "String does not contain valid number", s);
   char *endPtr;
   errno = 0;
-  auto value = strtoull(s.begin(), &endPtr, 10);
+  auto value = strtoull(s.begin(), &endPtr, isHex(s.cStr()) ? 16 : 10);
   KJ_REQUIRE(endPtr == s.end(), "String does not contain valid number", s);
   KJ_REQUIRE(errno != ERANGE, "Value out-of-range", s);
   KJ_REQUIRE(value <= max, "Value out-of-range", value, max);

c++/src/kj/string.h

@@ -114,6 +114,11 @@ public:
 
   template <typename T>
   T parseAs() const;
+  // Parse string as template number type.
+  // Integer numbers prefixed by "0x" and "0X" are parsed in base 16 (like strtoi with base 0).
+  // Integer numbers prefixed by "0" are parsed in base 10 (unlike strtoi with base 0).
+  // Overflowed integer numbers throw exception.
+  // Overflowed floating numbers return inf.
 
 private:
   inline StringPtr(ArrayPtr<const char> content): content(content) {}