Fix warnings on Clang 8.

This re-implements (and adds tests for) CountLeadingSignBits.

Change-Id: I308254f2ca97251173bcc76ef046dae4a445b9b8

1 files changed, 61 insertions, 0 deletions

diff --git a/test/aarch64/test-api-aarch64.cc b/test/aarch64/test-api-aarch64.cc
index cca50374..1cb66cd7 100644
--- a/test/aarch64/test-api-aarch64.cc
+++ b/test/aarch64/test-api-aarch64.cc
@@ -41,6 +41,67 @@
 namespace vixl {
 namespace aarch64 {
 
+// Check compiler intrinsics helpers.
+
+TEST(count_leading_sign_bits) {
+  class Helper {
+   public:
+    static void Check(int64_t value, int non_sign_bits) {
+      VIXL_ASSERT((0 <= non_sign_bits) && (non_sign_bits < 64));
+
+      for (int width = 1; width <= 64; width *= 2) {
+        // Note that leading_sign_bits does not include the topmost bit.
+        int leading_sign_bits = width - non_sign_bits - 1;
+        if (leading_sign_bits < 0) continue;
+
+        int64_t result = CountLeadingSignBits(value, width);
+        int64_t fallback_result = CountLeadingSignBitsFallBack(value, width);
+        VIXL_CHECK(result == leading_sign_bits);
+        VIXL_CHECK(fallback_result == leading_sign_bits);
+      }
+    }
+  };
+
+  // Basic positive (and zero) cases. Sign bits are all zeroes.
+  Helper::Check(0, 0);  // 0b++++
+  Helper::Check(1, 1);  // 0b+++1
+  Helper::Check(2, 2);  // 0b++10
+  Helper::Check(3, 2);  // 0b++11
+  Helper::Check(4, 3);  // 0b+100
+
+  // Basic negative cases. Sign bits are all ones.
+  Helper::Check(-1, 0);  // 0b----
+  Helper::Check(-2, 1);  // 0b---0
+  Helper::Check(-3, 2);  // 0b--01
+  Helper::Check(-4, 2);  // 0b--00
+  Helper::Check(-5, 3);  // 0b-011
+
+  // Boundary conditions.
+  Helper::Check(INT8_MAX, 7);
+  Helper::Check(INT8_MIN, 7);
+  Helper::Check(static_cast<int64_t>(INT8_MAX) + 1, 8);
+  Helper::Check(static_cast<int64_t>(INT8_MIN) - 1, 8);
+
+  Helper::Check(INT16_MAX, 15);
+  Helper::Check(INT16_MIN, 15);
+  Helper::Check(static_cast<int64_t>(INT16_MAX) + 1, 16);
+  Helper::Check(static_cast<int64_t>(INT16_MIN) - 1, 16);
+
+  Helper::Check(INT32_MAX, 31);
+  Helper::Check(INT32_MIN, 31);
+  Helper::Check(static_cast<int64_t>(INT32_MAX) + 1, 32);
+  Helper::Check(static_cast<int64_t>(INT32_MIN) - 1, 32);
+
+  Helper::Check(INT64_MAX, 63);
+  Helper::Check(INT64_MIN, 63);
+
+  // Check automatic width detection.
+  VIXL_CHECK(CountLeadingSignBits(static_cast<int8_t>(42)) == 1);  // 0b00101010
+  VIXL_CHECK(CountLeadingSignBits(static_cast<int16_t>(42)) == 9);
+  VIXL_CHECK(CountLeadingSignBits(static_cast<int32_t>(42)) == 25);
+  VIXL_CHECK(CountLeadingSignBits(static_cast<int64_t>(42)) == 57);
+}
+
 // Check SimFloat16 class mechanics.
 TEST(float16_operators) {
   ::vixl::internal::SimFloat16 f1 = kFP16DefaultNaN;