[libc-commits] [libc] [libc][stdfix] Implement `countlsfx` functions in libc. (PR #126597)

[Krishna Pandey via libc-commits]

================
@@ -0,0 +1,61 @@
+//===-- Utility class to test countls -------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "test/UnitTest/Test.h"
+
+#include "src/__support/fixed_point/fx_rep.h"
+
+template <typename T> class CountlsTest : public LIBC_NAMESPACE::testing::Test {
+
+  using FXRep = LIBC_NAMESPACE::fixed_point::FXRep<T>;
+  static constexpr T zero = FXRep::ZERO();
+  static constexpr T max = FXRep::MAX();
+  static constexpr T min = FXRep::MIN();
+  static constexpr T one_half = FXRep::ONE_HALF();
+  static constexpr T one_fourth = FXRep::ONE_FOURTH();
+  static constexpr T eps = FXRep::EPS();
+
+public:
+  typedef int (*CountlsFunc)(T);
+
+  void testSpecialNumbers(CountlsFunc func) {
+    constexpr bool is_signed = (FXRep::SIGN_LEN > 0);
+
+    EXPECT_EQ(FXRep::INTEGRAL_LEN, func(one_half));
+    EXPECT_EQ(FXRep::INTEGRAL_LEN + 1, func(one_fourth));
+    EXPECT_EQ(FXRep::VALUE_LEN, func(zero));
+    EXPECT_EQ(FXRep::VALUE_LEN - 1, func(eps));
+    EXPECT_EQ(0, func(max));
+    // If signed, left shifting the minimum value will overflow, so countls = 0.
+    // If unsigned, the minimum value is zero, so countls is the number of value
+    // bits according to ISO/IEC TR 18037.
+    EXPECT_EQ(is_signed ? 0 : FXRep::VALUE_LEN, func(min));
+
+    if (10 <= static_cast<int>(max)) {
+      EXPECT_EQ(FXRep::INTEGRAL_LEN - 4, func(10));
+    }
+
+    if (static_cast<int>(min) <= -10) {
+      EXPECT_EQ(FXRep::INTEGRAL_LEN - 4, func(-10));
+    }
+
+    if constexpr (is_signed) {
+      EXPECT_EQ(FXRep::VALUE_LEN, func(-zero));
+      EXPECT_EQ(FXRep::VALUE_LEN, func(-eps));
+      EXPECT_EQ(FXRep::INTEGRAL_LEN + 1, func(-one_half));
+      if (FXRep::FRACTION_LEN >= 2) {
+        EXPECT_EQ(FXRep::INTEGRAL_LEN + 2, func(-one_fourth));
+      }
----------------
krishna2803 wrote:

fixed here:
https://github.com/llvm/llvm-project/blob/8790b2c010563947cb2c87c15e7cbf3ba46b31f1/libc/test/src/stdfix/CountlsTest.h#L39-L51

https://github.com/llvm/llvm-project/pull/126597