TheRock/rocm-systems/projects/hip-tests/catch/unit/deviceLib/hipTestHalfConstexpr.cc

/*
 * Copyright (c) Advanced Micro Devices, Inc., or its affiliates.
 *
 * SPDX-License-Identifier: MIT
 */


#include <hip/hip_fp16.h>
#include <hip_test_common.hh>
#include <cmath>


constexpr unsigned short kHalfTwo = 0x4000U;       // 2.0
constexpr unsigned short kHalfPi = 0x4248U;        // ~3.140625 (closest to pi)
constexpr unsigned short kHalfInf = 0x7C00U;       // +Infinity

/**
 * Constexpr function to create __half from bit pattern.
 * This pattern is used by libhipcxx for mathematical constants.
 */
__host__ __device__ constexpr __half makeHalfFromBits(unsigned short bits) {
  return __half{__half_raw{.x = bits}};
}

// Constexpr half-precision constants using the pattern from the bug report

constexpr __half kConstTwo = makeHalfFromBits(kHalfTwo);
constexpr __half kConstPi = makeHalfFromBits(kHalfPi);

/**
 * Device kernel that uses constexpr __half values.
 * Tests that constexpr __half can be used in device code.
 */
__global__ void testConstexprHalfDevice(float* results) {

  // Verify the constexpr values are usable in device code
  results[0] = __half2float(kConstTwo);
  results[1]= __half2float(kConstPi);

  // Test arithmetic with constexpr values
  results[2] = __half2float(__hmul(kConstTwo, kConstPi));   // 2 * pi
}

/**
 * Test Description
 * ------------------------
 * - Tests constexpr construction of __half from __half_raw{.x = bits}
 * - This is the pattern used by libhipcxx for mathematical constants
 * - Verifies fix for union active member issue in constexpr evaluation
 */
HIP_TEST_CASE(Unit_hipTestHalfConstexpr_HostConstexpr) {
  // Test that constexpr __half values have correct bit patterns on host

  SECTION("Two") {
    constexpr __half two = makeHalfFromBits(kHalfTwo);
    float f = __half2float(two);
    REQUIRE(f == 2.0f);
    REQUIRE(__half_as_ushort(two) == kHalfTwo);
  }

  SECTION("Pi approximation") {
    constexpr __half pi = makeHalfFromBits(kHalfPi);
    float f = __half2float(pi);
    // Half precision pi is approximately 3.140625
    REQUIRE(f == Catch::Approx(3.14159f).epsilon(0.01));
    REQUIRE(__half_as_ushort(pi) == kHalfPi);
  }

  SECTION("Infinity") {
    constexpr __half inf = makeHalfFromBits(kHalfInf);
    REQUIRE(__hisinf(inf));
    REQUIRE(__half_as_ushort(inf) == kHalfInf);
  }

  SECTION("File scope constexpr values") {
    // Test that file-scope constexpr values are correct
    REQUIRE(__half2float(kConstTwo) == 2.0f);
  }
}

/**
 * Test Description
 * ------------------------
 * - Tests that constexpr __half values can be used in device kernels
 * - Verifies both file-scope and kernel-local constexpr values work
 */
HIP_TEST_CASE(Unit_hipTestHalfConstexpr_DeviceConstexpr) {
  constexpr size_t numResults = 3;
  float* results_d = nullptr;
  std::vector<float> results_h(numResults, 0.0f);

  HIP_CHECK(hipMalloc(&results_d, numResults * sizeof(float)));

  testConstexprHalfDevice<<<1, 1>>>(results_d);
  HIP_CHECK(hipDeviceSynchronize());

  HIP_CHECK(hipMemcpy(results_h.data(), results_d, numResults * sizeof(float),
                      hipMemcpyDeviceToHost));

  // Verify results
  REQUIRE(results_h[0] == 2.0f);       // kConstTwo
  REQUIRE(results_h[1] == Catch::Approx(3.14159f).epsilon(0.01));  // kConstPi
  REQUIRE(results_h[2] == Catch::Approx(6.28f).epsilon(0.01));  // 2 * pi

  HIP_CHECK(hipFree(results_d));
}