address PR feedback from @asl

---------

Co-authored-by: Anton Korobeynikov <anton@korobeynikov.info>

BUILD.bazel

@@ -48,6 +48,7 @@ cc_library(
         ":config_h",
         "@boost//:format",
         "@boost//:multiprecision",
+        "@com_google_absl//absl/numeric:bits",
         "@com_google_googletest//:gtest",
     ],
 )

lib/CMakeLists.txt

@@ -93,3 +93,4 @@ add_library(p4ctoolkit STATIC ${LIBP4CTOOLKIT_SRCS})
 
 # Disable libcall (realloc, malloc) optimizations which may cause infinite loops.
 set_target_properties(p4ctoolkit PROPERTIES COMPILE_FLAGS -fno-builtin)
+target_link_libraries(p4ctoolkit PRIVATE absl::bits)

lib/bitrange.h

@@ -23,6 +23,7 @@ limitations under the License.
 #include <optional>
 #include <utility>
 
+#include "absl/numeric/bits.h"
 #include "bitvec.h"
 #include "exceptions.h"
 #include "hash.h"
@@ -65,29 +66,27 @@ class JSONLoader;
 namespace BitRange {
 
 namespace Detail {
-#if defined(__GNUC__) || defined(__clang__)
 /**
- * @return boolean indicating if @p value is a power of two.
+ * @return find the bit position of the first one bit
+ *
+ * Will return all-ones if no bit is set
  *
  * This function is declared constexpr to allow it to be used in tests to optimize code generation.
  */
-constexpr bool isPowerOfTwo(int value) { return value && !(value & (value - 1)); }
-
-constexpr int log2ForPowerOfTwo(int value) { return sizeof(value) * 8 - __builtin_clz(value) - 1; }
-#endif  // defined(__GNUC__) || defined(__clang__)
+constexpr unsigned ffs(unsigned value) { return sizeof(value) * 8 - absl::countl_zero(value) - 1; }
 
 /**
  * @return the result of dividing @dividend by @divisor, rounded towards
  * negative infinity. This is different than normal C++ integer division, which
  * rounds towards zero. For example, `-7 / 8 == 0`, but
  * `divideFloor(-7, 8) == -1`.
  */
-inline int divideFloor(int dividend, int divisor) {
+constexpr inline int divideFloor(int dividend, int divisor) {
 #if defined(__GNUC__) || defined(__clang__)
     // Code to enable compiler folding when the divisor is a power-of-two compile-time constant
     // In this case, compiler should fold to a right-shift
-    if (__builtin_constant_p(divisor) && isPowerOfTwo(divisor))
-        return dividend >> log2ForPowerOfTwo(divisor);
+    if (__builtin_constant_p(divisor) && absl::has_single_bit(static_cast<unsigned>(divisor)))
+        return dividend >> ffs(divisor);
 #endif  // defined(__GNUC__) || defined(__clang__)
 
     const int quotient = dividend / divisor;
@@ -120,11 +119,12 @@ constexpr int modulo(int dividend, int divisor) {
  *     dividends than for negative dividends.
  * To make this concrete, `-7 % 8 == -7`, but `moduloFloor(-7, 8) == 1`.
  */
-inline int moduloFloor(const int dividend, const int divisor) {
+constexpr inline int moduloFloor(const int dividend, const int divisor) {
 #if defined(__GNUC__) || defined(__clang__)
     // Code to enable compiler folding when the divisor is a power-of-two compile-time constant
     // In this case, compiler should fold to a bitwise-and
-    if (__builtin_constant_p(divisor) && isPowerOfTwo(divisor)) return dividend & (divisor - 1);
+    if (__builtin_constant_p(divisor) && absl::has_single_bit(static_cast<unsigned>(divisor)))
+        return dividend & (divisor - 1);
 #endif  // defined(__GNUC__) || defined(__clang__)
 
     const int remainder = modulo(dividend, divisor);

test/CMakeLists.txt

@@ -74,7 +74,7 @@ set (GTESTP4C_SOURCES ${GTEST_SOURCES} ${GTEST_BASE_SOURCES})
 include_directories(${CMAKE_CURRENT_BINARY_DIR}/test)
 configure_file(gtest/env.h.in ${CMAKE_CURRENT_BINARY_DIR}/gtest/env.h)
 add_executable (gtestp4c ${GTESTP4C_SOURCES})
-target_link_libraries (gtestp4c ${GTEST_LDADD} ${P4C_LIBRARIES} gtest ${P4C_LIB_DEPS})
+target_link_libraries (gtestp4c PUBLIC ${GTEST_LDADD} PUBLIC ${P4C_LIBRARIES} PUBLIC gtest PUBLIC ${P4C_LIB_DEPS})
 add_dependencies(gtestp4c gtest genIR frontend controlplane)
 
 # The load_ir_from_json test needs this file. Easier to copy to build directory
@@ -87,3 +87,4 @@ add_dependencies(gtestp4c copy_gtest_deps)
 # Tests
 add_test (NAME gtestp4c COMMAND gtestp4c WORKING_DIRECTORY ${P4C_BINARY_DIR})
 set_tests_properties (gtestp4c PROPERTIES LABELS "gtest")
+target_link_libraries(gtestp4c PRIVATE absl::bits)