PUBLIC:[P4-constraints] Don't use c strings so that trailing zeros ar…

…e not discarded when parsing an int from a bytestring.

PiperOrigin-RevId: 603786237

p4_constraints/backend/interpreter.cc

@@ -106,15 +106,13 @@ Integer ParseP4RTInteger(std::string int_str) {
   // allowing for non-canonical bytestrings.
   int_str.erase(0, int_str.find_first_not_of('\0'));
   mpz_class integer;
-  const char* chars = int_str.c_str();
-  const size_t char_count = strlen(chars);
   constexpr int most_significant_first = 1;
   constexpr size_t char_size = sizeof(char);
   static_assert(char_size == 1, "expected sizeof(char) == 1");
   constexpr int endian = 0;    // system default
   constexpr size_t nails = 0;  // don't skip any bits
-  mpz_import(integer.get_mpz_t(), char_count, most_significant_first, char_size,
-             endian, nails, chars);
+  mpz_import(integer.get_mpz_t(), int_str.size(), most_significant_first,
+             char_size, endian, nails, int_str.data());
   return integer;
 }
 

p4_constraints/backend/interpreter_test.cc

@@ -1287,6 +1287,17 @@ TEST(ParseP4RTInteger, ParsesZeroCorrectly) {
   ASSERT_EQ(zero_string.at(0), '\0');
   EXPECT_THAT(ParseP4RTInteger(zero_string), Eq(0));
 }
+
+TEST(ParseP4RTInteger, ParsesTrailingZeroCorrectly) {
+  std::string hex_string = {'\xe0', '\x00', '\x00'};
+  uint hex_sum = 0;
+  for (char c : hex_string) {
+    hex_sum <<= 8;
+    hex_sum += c;
+  }
+  EXPECT_THAT(ParseP4RTInteger(hex_string), Eq(hex_sum));
+}
+
 }  // namespace
 }  // namespace internal_interpreter
 }  // namespace p4_constraints