[libc-commits] [libc] [llvm] [libc][math] Implement single precision lgamma function (PR #205490)

[via libc-commits]

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+//===-- Unittests for lgammaf ---------------------------------------------===//
+//
+// 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 "hdr/stdint_proxy.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/libc_errno.h"
+#include "src/math/lgammaf.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
+#include "utils/MPFRWrapper/MPFRUtils.h"
+
+using LlvmLibcLgammafTest = LIBC_NAMESPACE::testing::FPTest<float>;
+
+namespace mpfr = LIBC_NAMESPACE::testing::mpfr;
+
+// Hard-to-round cases collected from prior exhaustive tests.
+// Each is a midpoint-case where small precision drift in the implementation
+// tips the double to float rounding direction.
+TEST_F(LlvmLibcLgammafTest, HardCases) {
+  static constexpr uint32_t INPUTS[] = {
+      0x77ac5740u, // 0x1.58ace8p+112 (huge positive, Stirling path)
+      0x87acf970u, // -0x1.f59f2ep-16  (small negative, reflection path)
+      0xc0afda0bu, // -0x1.5fb416p+1   (negative middle, reflection through M3)
+      0x3fc0737cu, // 0x1.80e6f8p+0    (medium near lgamma minimum)
+      0x3fc07be9u, // 0x1.80f7d2p+0    (same)
+      0x3fd0b2bfu, // 0x1.a1657ep+0    (same)
+      0xb3000824u, // -0x1.001048p-25  (tiny negative)
+      0x30f00a14u, // 0x1.e01428p-30   (tiny positive)
+      0x00800000u, // 0x1p-126         (min normal positive)
+      0x80800000u, // -0x1p-126        (min normal negative)
+      0x3f800000u, // 0x1p+0           (lgamma(1) = 0 exactly)
+      0x40000000u, // 0x1p+1           (lgamma(2) = 0 exactly)
+  };
+  for (uint32_t v : INPUTS) {
+    float x = FPBits(v).get_val();
+    libc_errno = 0;
+    float result = LIBC_NAMESPACE::lgammaf(x);
+    if (FPBits(result).is_nan() || FPBits(result).is_inf() || libc_errno != 0)
+      continue;
+    EXPECT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Lgamma, x,
+                                   LIBC_NAMESPACE::lgammaf(x), 0.5);
+  }
+}
+
+TEST_F(LlvmLibcLgammafTest, PositiveRange) {
+  constexpr uint32_t COUNT = 100'000;
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lntue wrote:

nit: Reduce these `COUNT` numbers in this file to `1'231` to reduce stress on the precommit CIs.  I'll replace all of those `1'231` values with a configurable cmake option later.

https://github.com/llvm/llvm-project/pull/205490