[libc-commits] [libc] [libc][math][c23] Add exp2f16 C23 math function (PR #101217)
via libc-commits
libc-commits at lists.llvm.org
Tue Jul 30 11:32:46 PDT 2024
https://github.com/overmighty created https://github.com/llvm/llvm-project/pull/101217
Part of #95250.
>From a3629e4d2dadb8fbe99fc22d4a6471fd1bfd3eb5 Mon Sep 17 00:00:00 2001
From: OverMighty <its.overmighty at gmail.com>
Date: Tue, 30 Jul 2024 20:12:17 +0200
Subject: [PATCH] [libc][math][c23] Add exp2f16 C23 math function
---
libc/config/linux/x86_64/entrypoints.txt | 1 +
libc/docs/math/index.rst | 2 +-
libc/spec/stdc.td | 1 +
libc/src/math/CMakeLists.txt | 1 +
libc/src/math/exp2f16.h | 21 +++
libc/src/math/generic/CMakeLists.txt | 22 +++
libc/src/math/generic/exp2f16.cpp | 134 ++++++++++++++++++
libc/test/src/math/CMakeLists.txt | 31 ++--
libc/test/src/math/exp2f16_test.cpp | 40 ++++++
.../math/performance_testing/CMakeLists.txt | 11 ++
.../math/performance_testing/exp2f16_perf.cpp | 22 +++
libc/test/src/math/smoke/CMakeLists.txt | 30 ++--
libc/test/src/math/smoke/exp2f16_test.cpp | 65 +++++++++
13 files changed, 361 insertions(+), 20 deletions(-)
create mode 100644 libc/src/math/exp2f16.h
create mode 100644 libc/src/math/generic/exp2f16.cpp
create mode 100644 libc/test/src/math/exp2f16_test.cpp
create mode 100644 libc/test/src/math/performance_testing/exp2f16_perf.cpp
create mode 100644 libc/test/src/math/smoke/exp2f16_test.cpp
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 0eb1690172a8e..f022d271235eb 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -564,6 +564,7 @@ if(LIBC_TYPES_HAS_FLOAT16)
libc.src.math.canonicalizef16
libc.src.math.ceilf16
libc.src.math.copysignf16
+ libc.src.math.exp2f16
libc.src.math.expf16
libc.src.math.f16add
libc.src.math.f16addf
diff --git a/libc/docs/math/index.rst b/libc/docs/math/index.rst
index 0448f8f36d2c2..c587ddc2372a9 100644
--- a/libc/docs/math/index.rst
+++ b/libc/docs/math/index.rst
@@ -290,7 +290,7 @@ Higher Math Functions
+-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
| exp10m1 | | | | | | 7.12.6.3 | F.10.3.3 |
+-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
-| exp2 | |check| | |check| | | | | 7.12.6.4 | F.10.3.4 |
+| exp2 | |check| | |check| | | |check| | | 7.12.6.4 | F.10.3.4 |
+-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
| exp2m1 | |check| | | | | | 7.12.6.5 | F.10.3.5 |
+-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
diff --git a/libc/spec/stdc.td b/libc/spec/stdc.td
index 788b9581cb2ab..a3fc9db64e046 100644
--- a/libc/spec/stdc.td
+++ b/libc/spec/stdc.td
@@ -577,6 +577,7 @@ def StdC : StandardSpec<"stdc"> {
FunctionSpec<"exp2", RetValSpec<DoubleType>, [ArgSpec<DoubleType>]>,
FunctionSpec<"exp2f", RetValSpec<FloatType>, [ArgSpec<FloatType>]>,
+ GuardedFunctionSpec<"exp2f16", RetValSpec<Float16Type>, [ArgSpec<Float16Type>], "LIBC_TYPES_HAS_FLOAT16">,
FunctionSpec<"exp2m1f", RetValSpec<FloatType>, [ArgSpec<FloatType>]>,
diff --git a/libc/src/math/CMakeLists.txt b/libc/src/math/CMakeLists.txt
index eb33532826ab8..7d80e48c7c6b6 100644
--- a/libc/src/math/CMakeLists.txt
+++ b/libc/src/math/CMakeLists.txt
@@ -101,6 +101,7 @@ add_math_entrypoint_object(expf16)
add_math_entrypoint_object(exp2)
add_math_entrypoint_object(exp2f)
+add_math_entrypoint_object(exp2f16)
add_math_entrypoint_object(exp2m1f)
diff --git a/libc/src/math/exp2f16.h b/libc/src/math/exp2f16.h
new file mode 100644
index 0000000000000..71361b997ae8e
--- /dev/null
+++ b/libc/src/math/exp2f16.h
@@ -0,0 +1,21 @@
+//===-- Implementation header for exp2f16 -----------------------*- 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_EXP2F16_H
+#define LLVM_LIBC_SRC_MATH_EXP2F16_H
+
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/properties/types.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+float16 exp2f16(float16 x);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_MATH_EXP2F16_H
diff --git a/libc/src/math/generic/CMakeLists.txt b/libc/src/math/generic/CMakeLists.txt
index f118742bddd68..f0e5c12760b08 100644
--- a/libc/src/math/generic/CMakeLists.txt
+++ b/libc/src/math/generic/CMakeLists.txt
@@ -1305,6 +1305,28 @@ add_entrypoint_object(
-O3
)
+add_entrypoint_object(
+ exp2f16
+ SRCS
+ exp2f16.cpp
+ HDRS
+ ../exp2f16.h
+ DEPENDS
+ libc.hdr.errno_macros
+ libc.hdr.fenv_macros
+ libc.src.__support.CPP.array
+ libc.src.__support.FPUtil.except_value_utils
+ libc.src.__support.FPUtil.fenv_impl
+ libc.src.__support.FPUtil.fp_bits
+ libc.src.__support.FPUtil.multiply_add
+ libc.src.__support.FPUtil.nearest_integer
+ libc.src.__support.FPUtil.polyeval
+ libc.src.__support.FPUtil.rounding_mode
+ libc.src.__support.macros.optimization
+ COMPILE_OPTIONS
+ -O3
+)
+
add_entrypoint_object(
exp2m1f
SRCS
diff --git a/libc/src/math/generic/exp2f16.cpp b/libc/src/math/generic/exp2f16.cpp
new file mode 100644
index 0000000000000..3f18ab9166a85
--- /dev/null
+++ b/libc/src/math/generic/exp2f16.cpp
@@ -0,0 +1,134 @@
+//===-- Half-precision 2^x 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/exp2f16.h"
+#include "hdr/errno_macros.h"
+#include "hdr/fenv_macros.h"
+#include "src/__support/CPP/array.h"
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/PolyEval.h"
+#include "src/__support/FPUtil/except_value_utils.h"
+#include "src/__support/FPUtil/multiply_add.h"
+#include "src/__support/FPUtil/nearest_integer.h"
+#include "src/__support/FPUtil/rounding_mode.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/optimization.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+static constexpr fputil::ExceptValues<float16, 3> EXP2F16_EXCEPTS = {{
+ // (input, RZ output, RU offset, RD offset, RN offset)
+ // x = 0x1.714p-11, exp2f16(x) = 0x1p+0 (RZ)
+ {0x11c5U, 0x3c00U, 1U, 0U, 1U},
+ // x = -0x1.558p-4, exp2f16(x) = 0x1.e34p-1 (RZ)
+ {0xad56U, 0x3b8dU, 1U, 0U, 0U},
+ // x = -0x1.d5cp-4, exp2f16(x) = 0x1.d8cp-1 (RZ)
+ {0xaf57U, 0x3b63U, 1U, 0U, 0U},
+}};
+
+// Generated by Sollya with the following commands:
+// > display = hexadecimal;
+// > for i from 0 to 7 do printsingle(round(2^(i * 2^-3), SG, RN));
+static constexpr cpp::array<uint32_t, 8> EXP2_MID_BITS = {
+ 0x3f80'0000U, 0x3f8b'95c2U, 0x3f98'37f0U, 0x3fa5'fed7U,
+ 0x3fb5'04f3U, 0x3fc5'672aU, 0x3fd7'44fdU, 0x3fea'c0c7U,
+};
+
+LLVM_LIBC_FUNCTION(float16, exp2f16, (float16 x)) {
+ using FPBits = fputil::FPBits<float16>;
+ FPBits x_bits(x);
+
+ uint16_t x_u = x_bits.uintval();
+ uint16_t x_abs = x_u & 0x7fffU;
+
+ // When |x| >= 16, or x is NaN.
+ if (LIBC_UNLIKELY(x_abs >= 0x4c00U)) {
+ // exp2(NaN) = NaN
+ if (x_bits.is_nan()) {
+ if (x_bits.is_signaling_nan()) {
+ fputil::raise_except_if_required(FE_INVALID);
+ return FPBits::quiet_nan().get_val();
+ }
+
+ return x;
+ }
+
+ // When x >= 16.
+ if (x_bits.is_pos()) {
+ // exp2(+inf) = +inf
+ if (x_bits.is_inf())
+ return FPBits::inf().get_val();
+
+ switch (fputil::quick_get_round()) {
+ case FE_TONEAREST:
+ case FE_UPWARD:
+ fputil::set_errno_if_required(ERANGE);
+ fputil::raise_except_if_required(FE_OVERFLOW);
+ return FPBits::inf().get_val();
+ default:
+ return FPBits::max_normal().get_val();
+ }
+ }
+
+ // When x <= -25.
+ if (x_u >= 0xce40U) {
+ // exp2(-inf) = +0
+ if (x_bits.is_inf())
+ return FPBits::zero().get_val();
+
+ fputil::set_errno_if_required(ERANGE);
+ fputil::raise_except_if_required(FE_UNDERFLOW | FE_INEXACT);
+
+ if (fputil::fenv_is_round_up())
+ return FPBits::min_subnormal().get_val();
+ return FPBits::zero().get_val();
+ }
+ }
+
+ if (auto r = EXP2F16_EXCEPTS.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
+ return r.value();
+
+ // For -25 < x < 16, to compute 2^x, we perform the following range reduction:
+ // find hi, mid, lo, such that:
+ // x = hi + mid + lo, in which
+ // hi is an integer,
+ // mid * 2^3 is an integer,
+ // -2^(-4) <= lo < 2^(-4).
+ // In particular,
+ // hi + mid = round(x * 2^3) * 2^(-3).
+ // Then,
+ // 2^x = 2^(hi + mid + lo) = 2^hi * 2^mid * 2^lo.
+ // We store 2^mid in the lookup table EXP2_MID_BITS, and compute 2^hi * 2^mid
+ // by adding hi to the exponent field of 2^mid. 2^lo is computed using a
+ // degree-3 minimax polynomial generated by Sollya.
+
+ float xf = x;
+ float kf = fputil::nearest_integer(xf * 0x1.0p+3f);
+ int x_hi_mid = static_cast<int>(kf);
+ int x_hi = x_hi_mid >> 3;
+ int x_mid = x_hi_mid & 0x7;
+ // lo = x - (hi + mid) = round(x * 2^3) * (-2^(-3)) + x
+ float lo = fputil::multiply_add(kf, -0x1.0p-3f, xf);
+
+ uint32_t exp2_hi_mid_bits =
+ EXP2_MID_BITS[x_mid] +
+ static_cast<uint32_t>(x_hi << fputil::FPBits<float>::FRACTION_LEN);
+ float exp2_hi_mid = fputil::FPBits<float>(exp2_hi_mid_bits).get_val();
+ // Degree-3 minimax polynomial generated by Sollya with the following
+ // commands:
+ // > display = hexadecimal;
+ // > P = fpminimax((2^x - 1)/x, 2, [|SG...|], [-2^-4, 2^-4]);
+ // > 1 + x * P;
+ float exp2_lo = fputil::polyeval(lo, 0x1p+0f, 0x1.62e43p-1f, 0x1.ec0aa6p-3f,
+ 0x1.c6b4a6p-5f);
+ return static_cast<float16>(exp2_hi_mid * exp2_lo);
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/test/src/math/CMakeLists.txt b/libc/test/src/math/CMakeLists.txt
index 56b27b0952b58..ebaabcb0dffe3 100644
--- a/libc/test/src/math/CMakeLists.txt
+++ b/libc/test/src/math/CMakeLists.txt
@@ -925,6 +925,19 @@ add_fp_unittest(
libc.src.math.expf16
)
+add_fp_unittest(
+ exp2_test
+ NEED_MPFR
+ SUITE
+ libc-math-unittests
+ SRCS
+ exp2_test.cpp
+ DEPENDS
+ libc.src.errno.errno
+ libc.src.math.exp2
+ libc.src.__support.FPUtil.fp_bits
+)
+
add_fp_unittest(
exp2f_test
NEED_MPFR
@@ -939,16 +952,14 @@ add_fp_unittest(
)
add_fp_unittest(
- exp2_test
- NEED_MPFR
- SUITE
- libc-math-unittests
- SRCS
- exp2_test.cpp
- DEPENDS
- libc.src.errno.errno
- libc.src.math.exp2
- libc.src.__support.FPUtil.fp_bits
+ exp2f16_test
+ NEED_MPFR
+ SUITE
+ libc-math-unittests
+ SRCS
+ exp2f16_test.cpp
+ DEPENDS
+ libc.src.math.exp2f16
)
add_fp_unittest(
diff --git a/libc/test/src/math/exp2f16_test.cpp b/libc/test/src/math/exp2f16_test.cpp
new file mode 100644
index 0000000000000..503d8c2d89d94
--- /dev/null
+++ b/libc/test/src/math/exp2f16_test.cpp
@@ -0,0 +1,40 @@
+//===-- Exhaustive test for exp2f16 ---------------------------------------===//
+//
+// 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/exp2f16.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
+#include "utils/MPFRWrapper/MPFRUtils.h"
+
+using LlvmLibcExp2f16Test = LIBC_NAMESPACE::testing::FPTest<float16>;
+
+namespace mpfr = LIBC_NAMESPACE::testing::mpfr;
+
+// Range: [0, Inf];
+static constexpr uint16_t POS_START = 0x0000U;
+static constexpr uint16_t POS_STOP = 0x7c00U;
+
+// Range: [-Inf, 0];
+static constexpr uint16_t NEG_START = 0x8000U;
+static constexpr uint16_t NEG_STOP = 0xfc00U;
+
+TEST_F(LlvmLibcExp2f16Test, PositiveRange) {
+ for (uint16_t v = POS_START; v <= POS_STOP; ++v) {
+ float16 x = FPBits(v).get_val();
+ EXPECT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Exp2, x,
+ LIBC_NAMESPACE::exp2f16(x), 0.5);
+ }
+}
+
+TEST_F(LlvmLibcExp2f16Test, NegativeRange) {
+ for (uint16_t v = NEG_START; v <= NEG_STOP; ++v) {
+ float16 x = FPBits(v).get_val();
+ EXPECT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Exp2, x,
+ LIBC_NAMESPACE::exp2f16(x), 0.5);
+ }
+}
diff --git a/libc/test/src/math/performance_testing/CMakeLists.txt b/libc/test/src/math/performance_testing/CMakeLists.txt
index b43d21a242f35..09211537d93f4 100644
--- a/libc/test/src/math/performance_testing/CMakeLists.txt
+++ b/libc/test/src/math/performance_testing/CMakeLists.txt
@@ -164,6 +164,17 @@ add_perf_binary(
-fno-builtin
)
+add_perf_binary(
+ exp2f16_perf
+ SRCS
+ exp2f16_perf.cpp
+ DEPENDS
+ .single_input_single_output_diff
+ libc.src.math.exp2f16
+ COMPILE_OPTIONS
+ -fno-builtin
+)
+
add_perf_binary(
expf_perf
SRCS
diff --git a/libc/test/src/math/performance_testing/exp2f16_perf.cpp b/libc/test/src/math/performance_testing/exp2f16_perf.cpp
new file mode 100644
index 0000000000000..aa58de2476f1a
--- /dev/null
+++ b/libc/test/src/math/performance_testing/exp2f16_perf.cpp
@@ -0,0 +1,22 @@
+//===-- Performance test for exp2f16 --------------------------------------===//
+//
+// 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 "SingleInputSingleOutputPerf.h"
+
+#include "src/math/exp2f16.h"
+
+// LLVM libc might be the only libc implementation with support for float16 math
+// functions currently. We can't compare our float16 functions against the
+// system libc, so we compare them against this placeholder function.
+static float16 placeholderf16(float16 x) { return x; }
+
+int main() {
+ SINGLE_INPUT_SINGLE_OUTPUT_PERF_EX(float16, LIBC_NAMESPACE::exp2f16,
+ ::placeholderf16, 20'000,
+ "exp2f16_perf.log")
+}
diff --git a/libc/test/src/math/smoke/CMakeLists.txt b/libc/test/src/math/smoke/CMakeLists.txt
index a59af91d76736..b49f6e0fa5663 100644
--- a/libc/test/src/math/smoke/CMakeLists.txt
+++ b/libc/test/src/math/smoke/CMakeLists.txt
@@ -977,6 +977,18 @@ add_fp_unittest(
libc.src.math.expf16
)
+add_fp_unittest(
+ exp2_test
+ SUITE
+ libc-math-smoke-tests
+ SRCS
+ exp2_test.cpp
+ DEPENDS
+ libc.src.errno.errno
+ libc.src.math.exp2
+ libc.src.__support.FPUtil.fp_bits
+)
+
add_fp_unittest(
exp2f_test
SUITE
@@ -990,15 +1002,15 @@ add_fp_unittest(
)
add_fp_unittest(
- exp2_test
- SUITE
- libc-math-smoke-tests
- SRCS
- exp2_test.cpp
- DEPENDS
- libc.src.errno.errno
- libc.src.math.exp2
- libc.src.__support.FPUtil.fp_bits
+ exp2f16_test
+ SUITE
+ libc-math-smoke-tests
+ SRCS
+ exp2f16_test.cpp
+ DEPENDS
+ libc.hdr.fenv_macros
+ libc.src.errno.errno
+ libc.src.math.exp2f16
)
add_fp_unittest(
diff --git a/libc/test/src/math/smoke/exp2f16_test.cpp b/libc/test/src/math/smoke/exp2f16_test.cpp
new file mode 100644
index 0000000000000..cd87e6134557a
--- /dev/null
+++ b/libc/test/src/math/smoke/exp2f16_test.cpp
@@ -0,0 +1,65 @@
+//===-- Unittests for exp2f16 ---------------------------------------------===//
+//
+// 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/fenv_macros.h"
+#include "src/errno/libc_errno.h"
+#include "src/math/exp2f16.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
+
+using LlvmLibcExp2f16Test = LIBC_NAMESPACE::testing::FPTest<float16>;
+
+TEST_F(LlvmLibcExp2f16Test, SpecialNumbers) {
+ LIBC_NAMESPACE::libc_errno = 0;
+
+ EXPECT_FP_EQ_ALL_ROUNDING(aNaN, LIBC_NAMESPACE::exp2f16(aNaN));
+ EXPECT_MATH_ERRNO(0);
+
+ EXPECT_FP_EQ_WITH_EXCEPTION(aNaN, LIBC_NAMESPACE::exp2f16(sNaN), FE_INVALID);
+ EXPECT_MATH_ERRNO(0);
+
+ EXPECT_FP_EQ_ALL_ROUNDING(inf, LIBC_NAMESPACE::exp2f16(inf));
+ EXPECT_MATH_ERRNO(0);
+
+ EXPECT_FP_EQ_ALL_ROUNDING(static_cast<float16>(zero),
+ LIBC_NAMESPACE::exp2f16(neg_inf));
+ EXPECT_MATH_ERRNO(0);
+
+ EXPECT_FP_EQ_ALL_ROUNDING(static_cast<float16>(1.0f),
+ LIBC_NAMESPACE::exp2f16(zero));
+ EXPECT_MATH_ERRNO(0);
+
+ EXPECT_FP_EQ_ALL_ROUNDING(static_cast<float16>(1.0f),
+ LIBC_NAMESPACE::exp2f16(neg_zero));
+ EXPECT_MATH_ERRNO(0);
+}
+
+TEST_F(LlvmLibcExp2f16Test, Overflow) {
+ LIBC_NAMESPACE::libc_errno = 0;
+
+ EXPECT_FP_EQ_WITH_EXCEPTION(inf, LIBC_NAMESPACE::exp2f16(max_normal),
+ FE_OVERFLOW);
+ EXPECT_MATH_ERRNO(ERANGE);
+
+ EXPECT_FP_EQ_WITH_EXCEPTION(
+ inf, LIBC_NAMESPACE::exp2f16(static_cast<float16>(16.0)), FE_OVERFLOW);
+ EXPECT_MATH_ERRNO(ERANGE);
+}
+
+TEST_F(LlvmLibcExp2f16Test, Underflow) {
+ LIBC_NAMESPACE::libc_errno = 0;
+
+ EXPECT_FP_EQ_WITH_EXCEPTION(zero, LIBC_NAMESPACE::exp2f16(neg_max_normal),
+ FE_UNDERFLOW | FE_INEXACT);
+ EXPECT_MATH_ERRNO(ERANGE);
+
+ EXPECT_FP_EQ_WITH_EXCEPTION(
+ zero, LIBC_NAMESPACE::exp2f16(static_cast<float16>(-25.0)),
+ FE_UNDERFLOW | FE_INEXACT);
+ EXPECT_MATH_ERRNO(ERANGE);
+}
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