[libc][C23][math] Implement cospif function correctly rounded for all rounding modes #97464

HendrikHuebner · 2024-07-02T19:39:23Z

I also fixed a comment in sinpif.cpp in the first commit. Should this be included in this PR?

All tests were passed, including the exhaustive test.

CC: @lntue

llvmbot · 2024-07-02T19:39:57Z

@llvm/pr-subscribers-libc

Author: Hendrik Hübner (HendrikHuebner)

Changes

I also fixed a comment in sinpif.cpp in the first commit. Should this be included in this PR?

All tests were passed, including the exhaustive test.

CC: @lntue

Patch is 20.44 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/97464.diff

18 Files Affected:

(modified) libc/config/darwin/arm/entrypoints.txt (+1)
(modified) libc/config/linux/aarch64/entrypoints.txt (+1)
(modified) libc/config/linux/riscv/entrypoints.txt (+1)
(modified) libc/config/linux/x86_64/entrypoints.txt (+1)
(modified) libc/docs/math/index.rst (+1-1)
(modified) libc/src/math/CMakeLists.txt (+1)
(added) libc/src/math/cospif.h (+18)
(modified) libc/src/math/generic/CMakeLists.txt (+17)
(added) libc/src/math/generic/cospif.cpp (+91)
(modified) libc/src/math/generic/sinpif.cpp (+3-3)
(modified) libc/test/src/math/CMakeLists.txt (+16)
(added) libc/test/src/math/cospif_test.cpp (+112)
(modified) libc/test/src/math/exhaustive/CMakeLists.txt (+16)
(added) libc/test/src/math/exhaustive/cospif_test.cpp (+33)
(modified) libc/test/src/math/smoke/CMakeLists.txt (+11)
(added) libc/test/src/math/smoke/cospif_test.cpp (+34)
(modified) libc/utils/MPFRWrapper/MPFRUtils.cpp (+19)
(modified) libc/utils/MPFRWrapper/MPFRUtils.h (+1)

diff --git a/libc/config/darwin/arm/entrypoints.txt b/libc/config/darwin/arm/entrypoints.txt
index cb4603c79c79c..d32745c9c9467 100644
--- a/libc/config/darwin/arm/entrypoints.txt
+++ b/libc/config/darwin/arm/entrypoints.txt
@@ -132,6 +132,7 @@ set(TARGET_LIBM_ENTRYPOINTS
     libc.src.math.coshf
     libc.src.math.cos
     libc.src.math.cosf
+    libc.src.math.cospif
     libc.src.math.erff
     libc.src.math.exp
     libc.src.math.expf
diff --git a/libc/config/linux/aarch64/entrypoints.txt b/libc/config/linux/aarch64/entrypoints.txt
index ff35e8fffec19..79e880b1bec8e 100644
--- a/libc/config/linux/aarch64/entrypoints.txt
+++ b/libc/config/linux/aarch64/entrypoints.txt
@@ -346,6 +346,7 @@ set(TARGET_LIBM_ENTRYPOINTS
     libc.src.math.cos
     libc.src.math.cosf
     libc.src.math.coshf
+    libc.src.math.cospif
     libc.src.math.erff
     libc.src.math.exp
     libc.src.math.exp10
diff --git a/libc/config/linux/riscv/entrypoints.txt b/libc/config/linux/riscv/entrypoints.txt
index 51d85eed9ff16..fb9e4e3763844 100644
--- a/libc/config/linux/riscv/entrypoints.txt
+++ b/libc/config/linux/riscv/entrypoints.txt
@@ -354,6 +354,7 @@ set(TARGET_LIBM_ENTRYPOINTS
     libc.src.math.cos
     libc.src.math.cosf
     libc.src.math.coshf
+    libc.src.math.cospif
     libc.src.math.erff
     libc.src.math.exp
     libc.src.math.exp10
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 3eefa129c9758..6a61b51d60242 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -371,6 +371,7 @@ set(TARGET_LIBM_ENTRYPOINTS
     libc.src.math.cos
     libc.src.math.cosf
     libc.src.math.coshf
+    libc.src.math.cospif
     libc.src.math.erff
     libc.src.math.exp
     libc.src.math.exp10
diff --git a/libc/docs/math/index.rst b/libc/docs/math/index.rst
index e4da3d42baf7a..6c84b10122677 100644
--- a/libc/docs/math/index.rst
+++ b/libc/docs/math/index.rst
@@ -274,7 +274,7 @@ Higher Math Functions
 +-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
 | cosh      | |check|          |                 |                        |                      |                        | 7.12.5.4               | F.10.2.4                   |
 +-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
-| cospi     |                  |                 |                        |                      |                        | 7.12.4.12              | F.10.1.12                  |
+| cospi     | |check|          |                 |                        |                      |                        | 7.12.4.12              | F.10.1.12                  |
 +-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
 | dsqrt     | N/A              | N/A             |                        | N/A                  |                        | 7.12.14.6              | F.10.11                    |
 +-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
diff --git a/libc/src/math/CMakeLists.txt b/libc/src/math/CMakeLists.txt
index 5b20913134fdf..ce4f8f993526d 100644
--- a/libc/src/math/CMakeLists.txt
+++ b/libc/src/math/CMakeLists.txt
@@ -81,6 +81,7 @@ add_math_entrypoint_object(cos)
 add_math_entrypoint_object(cosf)
 add_math_entrypoint_object(cosh)
 add_math_entrypoint_object(coshf)
+add_math_entrypoint_object(cospif)
 
 add_math_entrypoint_object(erf)
 add_math_entrypoint_object(erff)
diff --git a/libc/src/math/cospif.h b/libc/src/math/cospif.h
new file mode 100644
index 0000000000000..50935bc33e59d
--- /dev/null
+++ b/libc/src/math/cospif.h
@@ -0,0 +1,18 @@
+//===-- Implementation header for cospif ------------------------*- 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC_MATH_COSPIF_H
+#define LLVM_LIBC_SRC_MATH_COSPIF_H
+
+namespace LIBC_NAMESPACE {
+
+float cospif(float x);
+
+} // namespace LIBC_NAMESPACE
+
+#endif // LLVM_LIBC_SRC_MATH_COSPIF_H
diff --git a/libc/src/math/generic/CMakeLists.txt b/libc/src/math/generic/CMakeLists.txt
index d6ea8c54174b6..6ace14063bcb1 100644
--- a/libc/src/math/generic/CMakeLists.txt
+++ b/libc/src/math/generic/CMakeLists.txt
@@ -217,6 +217,23 @@ add_entrypoint_object(
     -O3
 )
 
+add_entrypoint_object(
+  cospif
+  SRCS
+    cospif.cpp
+  HDRS
+    ../cospif.h
+  DEPENDS
+    .sincosf_utils
+    libc.src.__support.FPUtil.fenv_impl
+    libc.src.__support.FPUtil.fp_bits
+    libc.src.__support.FPUtil.fma
+    libc.src.__support.FPUtil.multiply_add
+    libc.src.__support.macros.optimization
+  COMPILE_OPTIONS
+    -O3
+)
+
 add_entrypoint_object(
   sin
   SRCS
diff --git a/libc/src/math/generic/cospif.cpp b/libc/src/math/generic/cospif.cpp
new file mode 100644
index 0000000000000..707f76c087074
--- /dev/null
+++ b/libc/src/math/generic/cospif.cpp
@@ -0,0 +1,91 @@
+//===-- Single-precision cospi function -----------------------------------===//
+//
+// 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 "src/math/cospif.h"
+#include "sincosf_utils.h"
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/multiply_add.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/optimization.h"            // LIBC_UNLIKELY
+#include "src/__support/macros/properties/cpu_features.h" // LIBC_TARGET_CPU_HAS_FMA
+
+namespace LIBC_NAMESPACE {
+
+LLVM_LIBC_FUNCTION(float, cospif, (float x)) {
+  using FPBits = typename fputil::FPBits<float>;
+
+  FPBits xbits(x);
+  xbits.set_sign(Sign::POS);
+
+  uint32_t x_abs = xbits.uintval();
+  double xd = static_cast<double>(xbits.get_val());
+
+  // Range reduction:
+  // For |x| > 1/32, we perform range reduction as follows:
+  // Find k and y such that:
+  //   x = (k + y) * 1/32
+  //   k is an integer
+  //   |y| < 0.5
+  //
+  // This is done by performing:
+  //   k = round(x * 32)
+  //   y = x * 32 - k
+  //
+  // Once k and y are computed, we then deduce the answer by the cosine of sum
+  // formula:
+  //   cospi(x) = cos((k + y)*pi/32)
+  //          = cos(y*pi/32) * cos(k*pi/32) - sin(y*pi/32) * sin(k*pi/32)
+  // The values of sin(k*pi/32) and cos(k*pi/32) for k = 0..63 are precomputed
+  // and stored using a vector of 32 doubles. Sin(y*pi/32) and cos(y*pi/32) are
+  // computed using degree-7 and degree-6 minimax polynomials generated by
+  // Sollya respectively.
+
+  // The exhautive test passes for smaller values
+  if (LIBC_UNLIKELY(x_abs < 0x38A2'F984U)) {
+
+#if defined(LIBC_TARGET_CPU_HAS_FMA)
+    return fputil::multiply_add(xbits.get_val(), -0x1.0p-25f, 1.0f);
+#else
+    return static_cast<float>(fputil::multiply_add(xd, -0x1.0p-25, 1.0));
+#endif // LIBC_TARGET_CPU_HAS_FMA
+  }
+
+  // Numbers greater or equal to 2^23 are always integers or NaN
+  if (LIBC_UNLIKELY(x_abs >= 0x4B00'0000)) {
+
+    if (LIBC_UNLIKELY(x_abs < 0x4B80'0000)) {
+      return (x_abs & 0x1) ? -1.0f : 1.0f;
+    }
+
+    // x is inf or nan.
+    if (LIBC_UNLIKELY(x_abs >= 0x7f80'0000U)) {
+      if (x_abs == 0x7f80'0000U) {
+        fputil::set_errno_if_required(EDOM);
+        fputil::raise_except_if_required(FE_INVALID);
+      }
+      return x + FPBits::quiet_nan().get_val();
+    }
+
+    return 1.0f;
+  }
+
+  // Combine the results with the sine of sum formula:
+  //   cos(pi * x) = cos((k + y)*pi/32)
+  //          = cos(y*pi/32) * cos(k*pi/32) - sin(y*pi/32) * sin(k*pi/32)
+  //          = (cosm1_y + 1) * cos_k - sin_y * sin_k
+  //          = (cosm1_y * cos_k + cos_k) - sin_y * sin_k
+  double sin_k, cos_k, sin_y, cosm1_y;
+
+  sincospif_eval(xd, sin_k, cos_k, sin_y, cosm1_y);
+
+  return static_cast<float>(fputil::multiply_add(
+      sin_y, -sin_k, fputil::multiply_add(cosm1_y, cos_k, cos_k)));
+}
+
+} // namespace LIBC_NAMESPACE
diff --git a/libc/src/math/generic/sinpif.cpp b/libc/src/math/generic/sinpif.cpp
index 662263c9fc43e..05bdad3ab4d0e 100644
--- a/libc/src/math/generic/sinpif.cpp
+++ b/libc/src/math/generic/sinpif.cpp
@@ -26,13 +26,13 @@ LLVM_LIBC_FUNCTION(float, sinpif, (float x)) {
   double xd = static_cast<double>(x);
 
   // Range reduction:
-  // For |x| > pi/32, we perform range reduction as follows:
+  // For |x| > 1/32, we perform range reduction as follows:
   // Find k and y such that:
   //   x = (k + y) * 1/32
   //   k is an integer
   //   |y| < 0.5
-  // For small range (|x| < 2^45 when FMA instructions are available, 2^22
-  // otherwise), this is done by performing:
+  //
+  // This is done by performing:
   //   k = round(x * 32)
   //   y = x * 32 - k
   //
diff --git a/libc/test/src/math/CMakeLists.txt b/libc/test/src/math/CMakeLists.txt
index 637e6720400ff..0ae7464e8aa40 100644
--- a/libc/test/src/math/CMakeLists.txt
+++ b/libc/test/src/math/CMakeLists.txt
@@ -28,6 +28,22 @@ add_fp_unittest(
     libc.src.__support.FPUtil.fp_bits
 )
 
+add_fp_unittest(
+  cospif_test
+  NEED_MPFR
+  SUITE
+    libc-math-unittests
+  SRCS
+    cospif_test.cpp
+  HDRS
+    sdcomp26094.h
+  DEPENDS
+    libc.src.errno.errno
+    libc.src.math.cospif
+    libc.src.__support.CPP.array
+    libc.src.__support.FPUtil.fp_bits
+)
+
 add_fp_unittest(
   sinf_test
   NEED_MPFR
diff --git a/libc/test/src/math/cospif_test.cpp b/libc/test/src/math/cospif_test.cpp
new file mode 100644
index 0000000000000..8f34dc4a2f617
--- /dev/null
+++ b/libc/test/src/math/cospif_test.cpp
@@ -0,0 +1,112 @@
+//===-- Unittests for cospif ----------------------------------------------===//
+//
+// 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 "src/errno/libc_errno.h"
+#include "src/math/cospif.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/src/math/sdcomp26094.h"
+#include "utils/MPFRWrapper/MPFRUtils.h"
+
+using LlvmLibcCospifTest = LIBC_NAMESPACE::testing::FPTest<float>;
+
+using LIBC_NAMESPACE::testing::SDCOMP26094_VALUES;
+
+namespace mpfr = LIBC_NAMESPACE::testing::mpfr;
+
+TEST_F(LlvmLibcCospifTest, SpecialNumbers) {
+  LIBC_NAMESPACE::libc_errno = 0;
+
+  EXPECT_FP_EQ(aNaN, LIBC_NAMESPACE::cospif(aNaN));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ(1.0f, LIBC_NAMESPACE::cospif(0.0f));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ(1.0f, LIBC_NAMESPACE::cospif(-0.0f));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ(aNaN, LIBC_NAMESPACE::cospif(inf));
+  EXPECT_MATH_ERRNO(EDOM);
+
+  EXPECT_FP_EQ(aNaN, LIBC_NAMESPACE::cospif(neg_inf));
+  EXPECT_MATH_ERRNO(EDOM);
+}
+
+TEST_F(LlvmLibcCospifTest, SpecificBitPatterns) {
+  constexpr int N = 38;
+  constexpr uint32_t INPUTS[N] = {0x3f06'0a92U, // x = pi/6
+                                  0x3f3a'dc51U, // x = 0x1.75b8a2p-1f
+                                  0x3f49'0fdbU, // x = pi/4
+                                  0x3f86'0a92U, // x = pi/3
+                                  0x3fa7'832aU, // x = 0x1.4f0654p+0f
+                                  0x3fc9'0fdbU, // x = pi/2
+                                  0x4017'1973U, // x = 0x1.2e32e6p+1f
+                                  0x4049'0fdbU, // x = pi
+                                  0x4096'cbe4U, // x = 0x1.2d97c8p+2f
+                                  0x40c9'0fdbU, // x = 2*pi
+                                  0x433b'7490U, // x = 0x1.76e92p+7f
+                                  0x437c'e5f1U, // x = 0x1.f9cbe2p+7f
+                                  0x4619'9998U, // x = 0x1.33333p+13f
+                                  0x474d'246fU, // x = 0x1.9a48dep+15f
+                                  0x4afd'ece4U, // x = 0x1.fbd9c8p+22f
+                                  0x4c23'32e9U, // x = 0x1.4665d2p+25f
+                                  0x50a3'e87fU, // x = 0x1.47d0fep+34f
+                                  0x5239'47f6U, // x = 0x1.728fecp+37f
+                                  0x53b1'46a6U, // x = 0x1.628d4cp+40f
+                                  0x55ca'fb2aU, // x = 0x1.95f654p+44f
+                                  0x588e'f060U, // x = 0x1.1de0cp+50f
+                                  0x5c07'bcd0U, // x = 0x1.0f79ap+57f
+                                  0x5ebc'fddeU, // x = 0x1.79fbbcp+62f
+                                  0x5fa6'eba7U, // x = 0x1.4dd74ep+64f
+                                  0x61a4'0b40U, // x = 0x1.48168p+68f
+                                  0x6386'134eU, // x = 0x1.0c269cp+72f
+                                  0x6589'8498U, // x = 0x1.13093p+76f
+                                  0x6600'0001U, // x = 0x1.000002p+77f
+                                  0x664e'46e4U, // x = 0x1.9c8dc8p+77f
+                                  0x66b0'14aaU, // x = 0x1.602954p+78f
+                                  0x67a9'242bU, // x = 0x1.524856p+80f
+                                  0x6a19'76f1U, // x = 0x1.32ede2p+85f
+                                  0x6c55'da58U, // x = 0x1.abb4bp+89f
+                                  0x6f79'be45U, // x = 0x1.f37c8ap+95f
+                                  0x7276'69d4U, // x = 0x1.ecd3a8p+101f
+                                  0x7758'4625U, // x = 0x1.b08c4ap+111f
+                                  0xB8A2'F987U};
+
+  for (int i = 0; i < N; ++i) {
+    float x = FPBits(INPUTS[i]).get_val();
+    EXPECT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Cospi, x,
+                                   LIBC_NAMESPACE::cospif(x), 0.5);
+    EXPECT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Cospi, -x,
+                                   LIBC_NAMESPACE::cospif(-x), 0.5);
+  }
+}
+
+// For small values, sinpi(x) is pi * x.
+TEST_F(LlvmLibcCospifTest, SmallValues) {
+  float x = FPBits(0x1780'0000U).get_val();
+  EXPECT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Cospi, x,
+                                 LIBC_NAMESPACE::cospif(x), 0.5);
+
+  x = FPBits(0x0040'0000U).get_val();
+  EXPECT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Cospi, x,
+                                 LIBC_NAMESPACE::cospif(x), 0.5);
+}
+
+// SDCOMP-26094: check sinfpi in the cases for which the range reducer
+// returns values furthest beyond its nominal upper bound of pi/4.
+TEST_F(LlvmLibcCospifTest, SDCOMP_26094) {
+  for (uint32_t v : SDCOMP26094_VALUES) {
+    float x = FPBits((v)).get_val();
+    EXPECT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Cospi, x,
+                                   LIBC_NAMESPACE::cospif(x), 0.5);
+  }
+}
+
+// sinpi(-n) = -0.0
+// sinpi(+n) = +0.0
+TEST_F(LlvmLibcCospifTest, SignedZeros) {}
diff --git a/libc/test/src/math/exhaustive/CMakeLists.txt b/libc/test/src/math/exhaustive/CMakeLists.txt
index 412ca031d0e99..c5f75b51cbd9f 100644
--- a/libc/test/src/math/exhaustive/CMakeLists.txt
+++ b/libc/test/src/math/exhaustive/CMakeLists.txt
@@ -74,6 +74,22 @@ add_fp_unittest(
     -lpthread
 )
 
+add_fp_unittest(
+  cospif_test
+  NO_RUN_POSTBUILD
+  NEED_MPFR
+  SUITE
+    libc_math_exhaustive_tests
+  SRCS
+    cospif_test.cpp
+  DEPENDS
+    .exhaustive_test
+    libc.src.math.cospif
+    libc.src.__support.FPUtil.fp_bits
+  LINK_LIBRARIES
+    -lpthread
+)
+
 add_fp_unittest(
   sincosf_test
   NO_RUN_POSTBUILD
diff --git a/libc/test/src/math/exhaustive/cospif_test.cpp b/libc/test/src/math/exhaustive/cospif_test.cpp
new file mode 100644
index 0000000000000..59077d5909937
--- /dev/null
+++ b/libc/test/src/math/exhaustive/cospif_test.cpp
@@ -0,0 +1,33 @@
+//===-- Exhaustive test for cospif ----------------------------------------===//
+//
+// 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 "exhaustive_test.h"
+#include "src/math/cospif.h"
+#include "utils/MPFRWrapper/MPFRUtils.h"
+
+namespace mpfr = LIBC_NAMESPACE::testing::mpfr;
+
+using LlvmLibcCospifExhaustiveTest =
+    LlvmLibcUnaryOpExhaustiveMathTest<float, mpfr::Operation::Cospi,
+                                      LIBC_NAMESPACE::cospif>;
+
+static constexpr uint32_t POS_START = 0x0000'0000U;
+static constexpr uint32_t POS_STOP = 0x7f80'0000U;
+
+// Range: [0, Inf]
+TEST_F(LlvmLibcCospifExhaustiveTest, PostiveRange) {
+  test_full_range_all_roundings(POS_START, POS_STOP);
+}
+
+// Range: [-Inf, 0]
+static constexpr uint32_t NEG_START = 0xb000'0000U;
+static constexpr uint32_t NEG_STOP = 0xff80'0000U;
+
+TEST_F(LlvmLibcCospifExhaustiveTest, NegativeRange) {
+  test_full_range_all_roundings(NEG_START, NEG_STOP);
+}
diff --git a/libc/test/src/math/smoke/CMakeLists.txt b/libc/test/src/math/smoke/CMakeLists.txt
index 1b269edaa2477..72d04439e2d93 100644
--- a/libc/test/src/math/smoke/CMakeLists.txt
+++ b/libc/test/src/math/smoke/CMakeLists.txt
@@ -10,6 +10,17 @@ add_fp_unittest(
   DEPENDS
     libc.src.errno.errno
     libc.src.math.cosf
+)
+
+add_fp_unittest(
+  cospif_test
+  SUITE
+    libc-math-smoke-tests
+  SRCS
+    cospif_test.cpp
+  DEPENDS
+    libc.src.errno.errno
+    libc.src.math.cospif
     libc.src.__support.CPP.array
     libc.src.__support.FPUtil.fp_bits
 )
diff --git a/libc/test/src/math/smoke/cospif_test.cpp b/libc/test/src/math/smoke/cospif_test.cpp
new file mode 100644
index 0000000000000..cd3910c64cdd7
--- /dev/null
+++ b/libc/test/src/math/smoke/cospif_test.cpp
@@ -0,0 +1,34 @@
+//===-- Unittests for cospif ----------------------------------------------===//
+//
+// 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 "src/errno/libc_errno.h"
+#include "src/math/cospif.h"
+#include "test/UnitTest/FPMatcher.h"
+
+#include <stdint.h>
+
+using LlvmLibcCospifTest = LIBC_NAMESPACE::testing::FPTest<float>;
+
+TEST_F(LlvmLibcCospifTest, SpecialNumbers) {
+  LIBC_NAMESPACE::libc_errno = 0;
+
+  EXPECT_FP_EQ(aNaN, LIBC_NAMESPACE::cospif(aNaN));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ(0.0f, LIBC_NAMESPACE::cospif(0.0f));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ(-0.0f, LIBC_NAMESPACE::cospif(-0.0f));
+  EXPECT_MATH_ERRNO(0);
+
+  EXPECT_FP_EQ(aNaN, LIBC_NAMESPACE::cospif(inf));
+  EXPECT_MATH_ERRNO(EDOM);
+
+  EXPECT_FP_EQ(aNaN, LIBC_NAMESPACE::cospif(neg_inf));
+  EXPECT_MATH_ERRNO(EDOM);
+}
\ No newline at end of file
diff --git a/libc/utils/MPFRWrapper/MPFRUtils.cpp b/libc/utils/MPFRWrapper/MPFRUtils.cpp
index f0a653824bea2..9a5946059bd9a 100644
--- a/libc/utils/MPFRWrapper/MPFRUtils.cpp
+++ b/libc/utils/MPFRWrapper/MPFRUtils.cpp
@@ -239,6 +239,23 @@ class MPFRNumber {
     return result;
   }
 
+  MPFRNumber cospi() const {
+    MPFRNumber result(*this);
+
+#if MPFR_VERSION_MAJOR > 4 ||                                                  \
+    (MPFR_VERSION_MAJOR == 4 && MPFR_VERSION_MINOR >= 2)
+
+    mpfr_cospi(result.value, value, mpfr_rounding);
+#else
+    MPFRNumber value_pi(0.0, 1280);
+    mpfr_const_pi(value_pi.value, MPFR_RNDN);
+    mpfr_mul(value_pi.value, value_pi.value, value, MPFR_RNDN);
+    mpfr_cos(result.value, value_pi.value, mpfr_rounding);
+#endif
+
+    return result;
+  }
+
   MPFRNumber erf() const {
     MPFRNumber result(*this);
     mpfr_erf(result.value, value, mpfr_rounding);
@@ -675,6 +692,8 @@ unary_operation(Operation op, InputType input, unsigned int precision,
     return mpfrInput.cos();
   case Operation::Cosh:
     return mpfrInput.cosh();...
[truncated]

HendrikHuebner · 2024-07-02T19:53:49Z

The Core-Math tests have passed

libc/test/src/math/smoke/cospif_test.cpp

lntue · 2024-07-02T19:59:42Z

@zimmermann6

zimmermann6 · 2024-07-03T09:30:55Z

I get a failure for rounding down:

Running exhaustive check in --rndn mode...
all ok
Running exhaustive check in --rndz mode...
all ok
Running exhaustive check in --rndu mode...
all ok
Running exhaustive check in --rndd mode...
FAIL x=0x1.7408p+12 ref=0x0p+0 y=-0x0p+0

HendrikHuebner · 2024-07-03T09:35:05Z

hm, I'm not sure why those tests are failing. They pass when I run them locally. I'll run them again, maybe I changed something.

HendrikHuebner · 2024-07-03T10:15:00Z

Yeah I'm not getting any failures running ./check.sh --exhaustive cospif. Are you on the latest commit @zimmermann6 ?

zimmermann6 · 2024-07-03T11:23:54Z

I got a similar error with revision 94012aa:

Running exhaustive check in --rndd mode...
FAIL x=0x1.6c0008p+20 ref=0x0p+0 y=-0x0p+0

This is on a AMD EPYC 7282. I can send you my libllvmlibc.a by mail if you want.

HendrikHuebner · 2024-07-03T11:36:06Z

I can test it on an AMD EPYC 7713P later. Do you know what the buildbot runs on? It keeps failing as well which I also can't reproduce

zimmermann6 · 2024-07-03T11:38:00Z

no I don't know for the buildbot, sorry

lntue · 2024-07-03T22:36:23Z

@HendrikHuebner you can add the following test cases to smoke tests:

  EXPECT_FP_EQ_ALL_ROUNDING(zero, LIBC_NAMESPACE::cospif(0.5f));
  EXPECT_FP_EQ_ALL_ROUNDING(neg_zero, LIBC_NAMESPACE::cospif(-0.5f));

lntue · 2024-07-04T13:47:04Z

libc/src/math/generic/cospif.cpp

+  double sin_k, cos_k, sin_y, cosm1_y;
+
+  sincospif_eval(xd, sin_k, cos_k, sin_y, cosm1_y);
+


Adding a similar test to your sinpif should fix the signed zero issue:

if (LIBC_UNLIKELY(sin_y == 0 && cos_k == 0)) return FPBits::zero(xbits.sign()).get_val();

github-actions · 2024-07-05T10:54:43Z

✅ With the latest revision this PR passed the C/C++ code formatter.

HendrikHuebner · 2024-07-06T11:11:10Z

Okay, I fixed the signed zero case. The buildbot passes now as well. My mpfr implementation for older mpfr version did not handle integer inputs correctly.

… rounding modes

zimmermann6 · 2024-07-08T07:44:46Z

I still get errors for n+1/2 when n is negative. IEEE 754-2019 says that cos(n+1/2) is always +0, whether n is positive or negative, so that cos(-x) = cos(x) always holds.

Running exhaustive check in --rndn mode...
FAIL x=-0x1.7408p+12 ref=0x0p+0 y=-0x0p+0
Running exhaustive check in --rndz mode...
FAIL x=-0x1.70008p+16 ref=0x0p+0 y=-0x0p+0
Running exhaustive check in --rndu mode...
FAIL x=-0x1.7408p+12 ref=0x0p+0 y=-0x0p+0
Running exhaustive check in --rndd mode...
FAIL x=-0x1.8p+0 ref=0x0p+0 y=-0x0p+0

HendrikHuebner · 2024-07-08T07:53:50Z

Yes, you are right. https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3096.pdf F.10.1.12.
I will patch this later today.

zimmermann6 · 2024-07-09T08:04:38Z

all exhaustive tests are ok now, thanks!

HendrikHuebner · 2024-07-09T08:46:07Z

Have you tested with the commit from my new PR? #98037

zimmermann6 · 2024-07-09T09:16:43Z

yes I tested with #98037, sorry my comment was in the wrong place

[libc][math][C23] Correct sinpif range reduction comment

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llvmbot added the libc label Jul 2, 2024

lntue self-requested a review July 2, 2024 19:42

lntue reviewed Jul 2, 2024

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[libc][C23][math] Implement cospif function correctly rounded for all…

a6c8dbd

… rounding modes

HendrikHuebner force-pushed the dev/libc-trigpi branch from f798632 to a6c8dbd Compare July 6, 2024 11:37

lntue approved these changes Jul 6, 2024

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lntue merged commit f8834ed into llvm:main Jul 6, 2024
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HendrikHuebner mentioned this pull request Jul 9, 2024

[libc][math][C23] Cospif function should only return unsigned zeros #98037

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[libc][C23][math] Implement cospif function correctly rounded for all rounding modes #97464

[libc][C23][math] Implement cospif function correctly rounded for all rounding modes #97464

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zimmermann6 commented Jul 9, 2024

		double sin_k, cos_k, sin_y, cosm1_y;

		sincospif_eval(xd, sin_k, cos_k, sin_y, cosm1_y);

[libc][C23][math] Implement cospif function correctly rounded for all rounding modes #97464

[libc][C23][math] Implement cospif function correctly rounded for all rounding modes #97464

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