[libc][math][c23] Add expf16 C23 math function #100632
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@llvm/pr-subscribers-libc Author: OverMighty (overmighty) ChangesPart of #95250. Full diff: https://github.com/llvm/llvm-project/pull/100632.diff 15 Files Affected:
diff --git a/libc/config/linux/aarch64/entrypoints.txt b/libc/config/linux/aarch64/entrypoints.txt
index 2334fed773702..25aa7834456ef 100644
--- a/libc/config/linux/aarch64/entrypoints.txt
+++ b/libc/config/linux/aarch64/entrypoints.txt
@@ -367,6 +367,7 @@ set(TARGET_LIBM_ENTRYPOINTS
libc.src.math.exp2
libc.src.math.exp2f
libc.src.math.expf
+ libc.src.math.expf16
libc.src.math.expm1
libc.src.math.expm1f
libc.src.math.fabs
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 035ceb8ca57bf..d7f51dc9163e3 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -393,6 +393,7 @@ set(TARGET_LIBM_ENTRYPOINTS
libc.src.math.exp2f
libc.src.math.exp2m1f
libc.src.math.expf
+ libc.src.math.expf16
libc.src.math.expm1
libc.src.math.expm1f
libc.src.math.fabs
diff --git a/libc/docs/math/index.rst b/libc/docs/math/index.rst
index 64de548a1ea1c..b047abc8ba858 100644
--- a/libc/docs/math/index.rst
+++ b/libc/docs/math/index.rst
@@ -284,7 +284,7 @@ Higher Math Functions
+-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
| erfc | | | | | | 7.12.8.2 | F.10.5.2 |
+-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
-| exp | |check| | |check| | | | | 7.12.6.1 | F.10.3.1 |
+| exp | |check| | |check| | | |check| | | 7.12.6.1 | F.10.3.1 |
+-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
| exp10 | |check| | |check| | | | | 7.12.6.2 | F.10.3.2 |
+-----------+------------------+-----------------+------------------------+----------------------+------------------------+------------------------+----------------------------+
diff --git a/libc/spec/stdc.td b/libc/spec/stdc.td
index d5a5cb6fedb4b..5f8490fe32ca6 100644
--- a/libc/spec/stdc.td
+++ b/libc/spec/stdc.td
@@ -573,6 +573,7 @@ def StdC : StandardSpec<"stdc"> {
FunctionSpec<"exp", RetValSpec<DoubleType>, [ArgSpec<DoubleType>]>,
FunctionSpec<"expf", RetValSpec<FloatType>, [ArgSpec<FloatType>]>,
+ GuardedFunctionSpec<"expf16", RetValSpec<Float16Type>, [ArgSpec<Float16Type>], "LIBC_TYPES_HAS_FLOAT16">,
FunctionSpec<"exp2", RetValSpec<DoubleType>, [ArgSpec<DoubleType>]>,
FunctionSpec<"exp2f", RetValSpec<FloatType>, [ArgSpec<FloatType>]>,
diff --git a/libc/src/math/CMakeLists.txt b/libc/src/math/CMakeLists.txt
index d70af33522d2b..323ce988f8613 100644
--- a/libc/src/math/CMakeLists.txt
+++ b/libc/src/math/CMakeLists.txt
@@ -97,6 +97,7 @@ add_math_entrypoint_object(erff)
add_math_entrypoint_object(exp)
add_math_entrypoint_object(expf)
+add_math_entrypoint_object(expf16)
add_math_entrypoint_object(exp2)
add_math_entrypoint_object(exp2f)
diff --git a/libc/src/math/expf16.h b/libc/src/math/expf16.h
new file mode 100644
index 0000000000000..8547f65f942d7
--- /dev/null
+++ b/libc/src/math/expf16.h
@@ -0,0 +1,21 @@
+//===-- Implementation header for expf16 ------------------------*- 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_EXPF16_H
+#define LLVM_LIBC_SRC_MATH_EXPF16_H
+
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/properties/types.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+float16 expf16(float16 x);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_MATH_EXPF16_H
diff --git a/libc/src/math/generic/CMakeLists.txt b/libc/src/math/generic/CMakeLists.txt
index 80e862542e29c..73c19eeaa0094 100644
--- a/libc/src/math/generic/CMakeLists.txt
+++ b/libc/src/math/generic/CMakeLists.txt
@@ -1226,6 +1226,27 @@ add_entrypoint_object(
-O3
)
+add_entrypoint_object(
+ expf16
+ SRCS
+ expf16.cpp
+ HDRS
+ ../expf16.h
+ DEPENDS
+ libc.hdr.errno_macros
+ libc.hdr.fenv_macros
+ libc.src.__support.CPP.array
+ libc.src.__support.FPUtil.fenv_impl
+ libc.src.__support.FPUtil.fp_bits
+ libc.src.__support.FPUtil.polyeval
+ libc.src.__support.FPUtil.multiply_add
+ libc.src.__support.FPUtil.nearest_integer
+ libc.src.__support.FPUtil.rounding_mode
+ libc.src.__support.macros.optimization
+ COMPILE_OPTIONS
+ -O3
+)
+
add_entrypoint_object(
exp2
SRCS
diff --git a/libc/src/math/generic/expf16.cpp b/libc/src/math/generic/expf16.cpp
new file mode 100644
index 0000000000000..53cac48c3c49b
--- /dev/null
+++ b/libc/src/math/generic/expf16.cpp
@@ -0,0 +1,153 @@
+//===-- Half-precision e^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/expf16.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, 5> EXPF16_EXCEPTS = {{
+ // (input, RZ output, RU offset, RD offset, RN offset)
+ // x = 0x1.de4p-8, expf16(x) = 0x1.01cp+0 (RZ)
+ {0x1f79U, 0x3c07U, 1U, 0U, 0U},
+ // x = 0x1.73cp-6, expf16(x) = 0x1.05cp+0 (RZ)
+ {0x25cfU, 0x3c17U, 1U, 0U, 0U},
+ // x = 0x1.c34p+0, expf16(x) = 0x1.74cp+2 (RZ)
+ {0x3f0dU, 0x45d3U, 1U, 0U, 1U},
+ // x = -0x1.488p-5, expf16(x) = 0x1.ebcp-1 (RZ)
+ {0xa922U, 0x3bafU, 1U, 0U, 0U},
+ // x = -0x1.55p-5, expf16(x) = 0x1.ebp-1 (RZ)
+ {0xa954U, 0x3bacU, 1U, 0U, 0U},
+}};
+
+// Generated by Sollya with the following commands:
+// > display = hexadecimal;
+// > for i from -18 to 12 do print(round(exp(i), SG, RN));
+static constexpr cpp::array<float, 31> EXP_HI = {
+ 0x1.05a628p-26f, 0x1.639e32p-25f, 0x1.e355bcp-24f, 0x1.4875cap-22f,
+ 0x1.be6c7p-21f, 0x1.2f6054p-19f, 0x1.9c54c4p-18f, 0x1.183542p-16f,
+ 0x1.7cd79cp-15f, 0x1.02cf22p-13f, 0x1.5fc21p-12f, 0x1.de16bap-11f,
+ 0x1.44e52p-9f, 0x1.b993fep-8f, 0x1.2c155cp-6f, 0x1.97db0cp-5f,
+ 0x1.152aaap-3f, 0x1.78b564p-2f, 0x1p+0f, 0x1.5bf0a8p+1f,
+ 0x1.d8e64cp+2f, 0x1.415e5cp+4f, 0x1.b4c902p+5f, 0x1.28d38ap+7f,
+ 0x1.936dc6p+8f, 0x1.122886p+10f, 0x1.749ea8p+11f, 0x1.fa7158p+12f,
+ 0x1.5829dcp+14f, 0x1.d3c448p+15f, 0x1.3de166p+17f,
+};
+
+// Generated by Sollya with the following commands:
+// > display = hexadecimal;
+// > for i from 0 to 7 do print(round(exp(i * 2^-3), SG, RN));
+static constexpr cpp::array<float, 8> EXP_MID = {
+ 0x1p+0f, 0x1.221604p+0f, 0x1.48b5e4p+0f, 0x1.747a52p+0f,
+ 0x1.a61298p+0f, 0x1.de455ep+0f, 0x1.0ef9dcp+1f, 0x1.330e58p+1f,
+};
+
+LLVM_LIBC_FUNCTION(float16, expf16, (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| >= 12, or x is NaN.
+ if (LIBC_UNLIKELY(x_abs >= 0x4a00U)) {
+ // exp(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 >= 12.
+ if (x_bits.is_pos() && x_u >= 0x4a00U) {
+ // exp(+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 <= -18.
+ if (x_u >= 0xcc80U) {
+ // exp(-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);
+
+ switch (fputil::quick_get_round()) {
+ case FE_UPWARD:
+ return FPBits::min_subnormal().get_val();
+ default:
+ return FPBits::zero().get_val();
+ }
+ }
+ }
+
+ if (auto r = EXPF16_EXCEPTS.lookup(x_u); LIBC_UNLIKELY(r.has_value()))
+ return r.value();
+
+ // For -18 < x < 12, to compute exp(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,
+ // exp(x) = exp(hi + mid + lo) = exp(hi) * exp(mid) * exp(lo).
+ // We store exp(hi) and exp(mid) in the lookup tables EXP_HI and EXP_MID
+ // respectively. exp(lo) is computed using a degree-3 minimax polynomial
+ // generated by Sollya.
+
+ float xf = static_cast<float>(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);
+
+ float exp_hi = EXP_HI[x_hi + 18];
+ float exp_mid = EXP_MID[x_mid];
+ // Degree-3 minimax polynomial generated by Sollya with the following
+ // commands:
+ // > display = hexadecimal;
+ // > P = fpminimax(expm1(x)/x, 2, [|SG...|], [-2^-4, 2^-4]);
+ // > P;
+ float exp_lo =
+ fputil::polyeval(lo, 0x1p+0f, 0x1p+0f, 0x1.001p-1f, 0x1.555ddep-3f);
+ return static_cast<float16>(exp_hi * exp_mid * exp_lo);
+}
+
+} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/test/UnitTest/FPMatcher.h b/libc/test/UnitTest/FPMatcher.h
index 6b50f3d23075a..2749908ef1849 100644
--- a/libc/test/UnitTest/FPMatcher.h
+++ b/libc/test/UnitTest/FPMatcher.h
@@ -74,7 +74,8 @@ template <typename T> struct FPTest : public Test {
static constexpr T inf = FPBits::inf(Sign::POS).get_val();
static constexpr T neg_inf = FPBits::inf(Sign::NEG).get_val();
static constexpr T min_normal = FPBits::min_normal().get_val();
- static constexpr T max_normal = FPBits::max_normal().get_val();
+ static constexpr T max_normal = FPBits::max_normal(Sign::POS).get_val();
+ static constexpr T neg_max_normal = FPBits::max_normal(Sign::NEG).get_val();
static constexpr T min_denormal = FPBits::min_subnormal().get_val();
static constexpr T max_denormal = FPBits::max_subnormal().get_val();
diff --git a/libc/test/src/math/CMakeLists.txt b/libc/test/src/math/CMakeLists.txt
index 3ad5d98858165..d57e220f98b82 100644
--- a/libc/test/src/math/CMakeLists.txt
+++ b/libc/test/src/math/CMakeLists.txt
@@ -888,6 +888,19 @@ add_fp_unittest(
libc.src.__support.FPUtil.fp_bits
)
+add_fp_unittest(
+ exp_test
+ NEED_MPFR
+ SUITE
+ libc-math-unittests
+ SRCS
+ exp_test.cpp
+ DEPENDS
+ libc.src.errno.errno
+ libc.src.math.exp
+ libc.src.__support.FPUtil.fp_bits
+)
+
add_fp_unittest(
expf_test
NEED_MPFR
@@ -902,16 +915,14 @@ add_fp_unittest(
)
add_fp_unittest(
- exp_test
- NEED_MPFR
- SUITE
- libc-math-unittests
- SRCS
- exp_test.cpp
- DEPENDS
- libc.src.errno.errno
- libc.src.math.exp
- libc.src.__support.FPUtil.fp_bits
+ expf16_test
+ NEED_MPFR
+ SUITE
+ libc-math-unittests
+ SRCS
+ expf16_test.cpp
+ DEPENDS
+ libc.src.math.expf16
)
add_fp_unittest(
diff --git a/libc/test/src/math/expf16_test.cpp b/libc/test/src/math/expf16_test.cpp
new file mode 100644
index 0000000000000..ee89a9c716e12
--- /dev/null
+++ b/libc/test/src/math/expf16_test.cpp
@@ -0,0 +1,40 @@
+//===-- Exhaustive test for expf16 ----------------------------------------===//
+//
+// 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/expf16.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
+#include "utils/MPFRWrapper/MPFRUtils.h"
+
+using LlvmLibcExpf16Test = 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(LlvmLibcExpf16Test, PositiveRange) {
+ for (uint16_t v = POS_START; v <= POS_STOP; ++v) {
+ float16 x = FPBits(v).get_val();
+ EXPECT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Exp, x,
+ LIBC_NAMESPACE::expf16(x), 0.5);
+ }
+}
+
+TEST_F(LlvmLibcExpf16Test, NegativeRange) {
+ for (uint16_t v = NEG_START; v <= NEG_STOP; ++v) {
+ float16 x = FPBits(v).get_val();
+ EXPECT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Exp, x,
+ LIBC_NAMESPACE::expf16(x), 0.5);
+ }
+}
diff --git a/libc/test/src/math/performance_testing/CMakeLists.txt b/libc/test/src/math/performance_testing/CMakeLists.txt
index 536338bf2a56a..b43d21a242f35 100644
--- a/libc/test/src/math/performance_testing/CMakeLists.txt
+++ b/libc/test/src/math/performance_testing/CMakeLists.txt
@@ -175,6 +175,17 @@ add_perf_binary(
-fno-builtin
)
+add_perf_binary(
+ expf16_perf
+ SRCS
+ expf16_perf.cpp
+ DEPENDS
+ .single_input_single_output_diff
+ libc.src.math.expf16
+ COMPILE_OPTIONS
+ -fno-builtin
+)
+
add_perf_binary(
fabsf_perf
SRCS
diff --git a/libc/test/src/math/performance_testing/expf16_perf.cpp b/libc/test/src/math/performance_testing/expf16_perf.cpp
new file mode 100644
index 0000000000000..c1213689ff5e7
--- /dev/null
+++ b/libc/test/src/math/performance_testing/expf16_perf.cpp
@@ -0,0 +1,22 @@
+//===-- Performancel test for expf16 --------------------------------------===//
+//
+// 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/expf16.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::expf16,
+ ::placeholderf16, 20'000,
+ "expf16_perf.log")
+}
diff --git a/libc/test/src/math/smoke/CMakeLists.txt b/libc/test/src/math/smoke/CMakeLists.txt
index 5ddc88a38eb64..1f4e4ae483edf 100644
--- a/libc/test/src/math/smoke/CMakeLists.txt
+++ b/libc/test/src/math/smoke/CMakeLists.txt
@@ -940,6 +940,18 @@ add_fp_unittest(
libc.src.__support.FPUtil.fp_bits
)
+add_fp_unittest(
+ exp_test
+ SUITE
+ libc-math-smoke-tests
+ SRCS
+ exp_test.cpp
+ DEPENDS
+ libc.src.errno.errno
+ libc.src.math.exp
+ libc.src.__support.FPUtil.fp_bits
+)
+
add_fp_unittest(
expf_test
SUITE
@@ -953,15 +965,16 @@ add_fp_unittest(
)
add_fp_unittest(
- exp_test
- SUITE
- libc-math-smoke-tests
- SRCS
- exp_test.cpp
- DEPENDS
- libc.src.errno.errno
- libc.src.math.exp
- libc.src.__support.FPUtil.fp_bits
+ expf16_test
+ SUITE
+ libc-math-smoke-tests
+ SRCS
+ expf16_test.cpp
+ DEPENDS
+ libc.hdr.errno_macros
+ libc.hdr.fenv_macros
+ libc.src.errno.errno
+ libc.src.math.expf16
)
add_fp_unittest(
diff --git a/libc/test/src/math/smoke/expf16_test.cpp b/libc/test/src/math/smoke/expf16_test.cpp
new file mode 100644
index 0000000000000..f05ecd0dc4d0e
--- /dev/null
+++ b/libc/test/src/math/smoke/expf16_test.cpp
@@ -0,0 +1,66 @@
+//===-- Unittests for expf16 ----------------------------------------------===//
+//
+// 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/errno_macros.h"
+#include "hdr/fenv_macros.h"
+#include "src/errno/libc_errno.h"
+#include "src/math/expf16.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
+
+using LlvmLibcExpf16Test = LIBC_NAMESPACE::testing::FPTest<float16>;
+
+TEST_F(LlvmLibcExpf16Test, SpecialNumbers) {
+ LIBC_NAMESPACE::libc_errno = 0;
+
+ EXPECT_FP_EQ_ALL_ROUNDING(aNaN, LIBC_NAMESPACE::expf16(aNaN));
+ EXPECT_MATH_ERRNO(0);
+
+ EXPECT_FP_EQ_WITH_EXCEPTION(sNaN, LIBC_NAMESPACE::expf16(sNaN), FE_INVALID);
+ EXPECT_MATH_ERRNO(0);
+
+ EXPECT_FP_EQ_ALL_ROUNDING(inf, LIBC_NAMESPACE::expf16(inf));
+ EXPECT_MATH_ERRNO(0);
+
+ EXPECT_FP_EQ_ALL_ROUNDING(static_cast<float16>(zero),
+ LIBC_NAMESPACE::expf16(neg_inf));
+ EXPECT_MATH_ERRNO(0);
+
+ EXPECT_FP_EQ_ALL_ROUNDING(static_cast<float16>(1.0f),
+ LIBC_NAMESPACE::expf16(zero));
+ EXPECT_MATH_ERRNO(0);
+
+ EXPECT_FP_EQ_ALL_ROUNDING(static_cast<float16>(1.0f),
+ LIBC_NAMESPACE::expf16(neg_zero));
+ EXPECT_MATH_ERRNO(0);
+}
+
+TEST_F(LlvmLibcExpf16Test, Overflow) {
+ LIBC_NAMESPACE::libc_errno = 0;
+
+ EXPECT_FP_EQ_WITH_EXCEPTION(inf, LIBC_NAMESPACE::expf16(max_normal),
+ FE_OVERFLOW);
+ EXPECT_MATH_ERRNO(ERANGE);
+
+ EXPECT_FP_EQ_WITH_EXCEPTION(
+ inf, LIBC_NAMESPACE::expf16(static_cast<float16>(12.0)), FE_OVERFLOW);
+ EXPECT_MATH_ERRNO(ERANGE);
+}
+
+TEST_F(LlvmLibcExpf16Test, Underflow) {
+ LIBC_NAMESPACE::libc_errno = 0;
+
+ EXPECT_FP_EQ_WITH_EXCEPTION(zero, LIBC_NAMESPACE::expf16(neg_max_normal),
+ FE_UNDERFLOW | FE_INEXACT);
+ EXPECT_MATH_ERRNO(ERANGE);
+
+ EXPECT_FP_EQ_WITH_EXCEPTION(
+ zero, LIBC_NAMESPACE::expf16(static_cast<float16>(-18.0)),
+ FE_UNDERFLOW | FE_INEXACT);
+ EXPECT_MATH_ERRNO(ERANGE);
+}
|
overmighty
commented
Jul 25, 2024
libc/src/math/generic/expf16.cpp
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| // When |x| >= 12, or x is NaN. | ||
| if (LIBC_UNLIKELY(x_abs >= 0x4a00U)) { |
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Wrapping all of these special cases in a single if (LIBC_UNLIKELY(...)) reduced the average runtime in subnormal range:
- from 208 ns/op to 70 ns/op (4.6 s vs 1.6 s total time) without
-march=native, - from 17.1 ns/op to 16.1 ns/op (350 ms vs 330 ms total time) with
-march=native,
on i7-13700H.
libc/src/math/generic/expf16.cpp
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| // Degree-3 minimax polynomial generated by Sollya with the following | ||
| // commands: | ||
| // > display = hexadecimal; | ||
| // > P = fpminimax(expm1(x)/x, 2, [|SG...|], [-2^-4, 2^-4]); | ||
| // > P; | ||
| float exp_lo = | ||
| fputil::polyeval(lo, 0x1p+0f, 0x1p+0f, 0x1.001p-1f, 0x1.555ddep-3f); |
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I also tried with a degree-4 minimax polynomial, but it resulted in more exceptional values.
lntue
reviewed
Jul 26, 2024
lntue
reviewed
Jul 26, 2024
overmighty
commented
Jul 30, 2024
| // commands: | ||
| // > display = hexadecimal; | ||
| // > P = fpminimax(expm1(x)/x, 2, [|SG...|], [-2^-4, 2^-4]); | ||
| // > 1 + x * P; |
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Can we call 1 + x + P a minimax polynomial too, or only P?
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yes, we can, it is for sure minimax with respect to some metric
|
Before, on i7-13700H:
After:
|
lntue
approved these changes
Jul 30, 2024
|
LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/104/builds/3378 Here is the relevant piece of the build log for the reference: |
|
LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/71/builds/3369 Here is the relevant piece of the build log for the reference: |
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Part of #95250.