[libc] [llvm] [libc][math][c23] Implement higher math function `cbrtf16` in LLVM libc (PR #132484)
Krishna Pandey via llvm-commits
llvm-commits at lists.llvm.org
Sun Mar 23 05:01:24 PDT 2025
https://github.com/krishna2803 updated https://github.com/llvm/llvm-project/pull/132484
>From 07e24a567d92b698024b86193cc6ff4be12a53e4 Mon Sep 17 00:00:00 2001
From: krishna2803 <kpandey81930 at gmail.com>
Date: Sat, 22 Mar 2025 04:21:48 +0530
Subject: [PATCH 01/16] chore: change polynomial degree comment from 7 to 6
Signed-off-by: krishna2803 <kpandey81930 at gmail.com>
---
libc/src/math/generic/cbrtf.cpp | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/libc/src/math/generic/cbrtf.cpp b/libc/src/math/generic/cbrtf.cpp
index 71b23c4a8c742..868790ee7c7c0 100644
--- a/libc/src/math/generic/cbrtf.cpp
+++ b/libc/src/math/generic/cbrtf.cpp
@@ -22,7 +22,7 @@ namespace {
// Look up table for 2^(i/3) for i = 0, 1, 2.
constexpr double CBRT2[3] = {1.0, 0x1.428a2f98d728bp0, 0x1.965fea53d6e3dp0};
-// Degree-7 polynomials approximation of ((1 + x)^(1/3) - 1)/x for 0 <= x <= 1
+// Degree-6 polynomials approximation of ((1 + x)^(1/3) - 1)/x for 0 <= x <= 1
// generated by Sollya with:
// > for i from 0 to 15 do {
// P = fpminimax(((1 + x)^(1/3) - 1)/x, 6, [|D...|], [i/16, (i + 1)/16]);
>From f3860e1ea665a13d4078e0806883aa0f1a99aa10 Mon Sep 17 00:00:00 2001
From: krishna2803 <kpandey81930 at gmail.com>
Date: Sat, 22 Mar 2025 04:22:42 +0530
Subject: [PATCH 02/16] add: implement cbrtf16
Signed-off-by: krishna2803 <kpandey81930 at gmail.com>
---
libc/src/math/cbrtf16.h | 21 ++++
libc/src/math/generic/cbrtf16.cpp | 164 ++++++++++++++++++++++++++++++
2 files changed, 185 insertions(+)
create mode 100644 libc/src/math/cbrtf16.h
create mode 100644 libc/src/math/generic/cbrtf16.cpp
diff --git a/libc/src/math/cbrtf16.h b/libc/src/math/cbrtf16.h
new file mode 100644
index 0000000000000..bddb1eda0a9fa
--- /dev/null
+++ b/libc/src/math/cbrtf16.h
@@ -0,0 +1,21 @@
+//===-- Implementation header for cbrtf16 -----------------------*- 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_CBRTF16_H
+#define LLVM_LIBC_SRC_MATH_CBRTF16_H
+
+#include "src/__support/macros/config.h" // LIBC_NAMESPACE_DECL
+#include "src/__support/macros/properties/types.h" // float16
+
+namespace LIBC_NAMESPACE_DECL {
+
+float16 cbrtf16(float16 x);
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LLVM_LIBC_SRC_MATH_CBRTF16_H
diff --git a/libc/src/math/generic/cbrtf16.cpp b/libc/src/math/generic/cbrtf16.cpp
new file mode 100644
index 0000000000000..782f1bfd1b100
--- /dev/null
+++ b/libc/src/math/generic/cbrtf16.cpp
@@ -0,0 +1,164 @@
+//===-- Implementation of sqrtf16 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/cbrtf16.h"
+#include "hdr/fenv_macros.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/config.h"
+#include "src/__support/macros/optimization.h" // LIBC_UNLIKELY
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace {
+
+// Look up table for 2^(i/3) for i = 0, 1, 2 in single precision
+constexpr float CBRT2[3] = {0x1p0f, 0x1.428a3p0f, 0x1.965feap0f};
+
+// Degree-4 polynomials approximation of ((1 + x)^(1/3) - 1)/x for 0 <= x <= 1
+// generated by Sollya with:
+// > display=hexadecimal;
+// for i from 0 to 15 do {
+// P = fpminimax(((1 + x)^(1/3) - 1)/x, 4, [|SG...|], [i/16, (i + 1)/16]);
+// print("{", coeff(P, 0), ",", coeff(P, 1), ",", coeff(P, 2), ",",
+// coeff(P, 3), coeff(P, 4),"},");
+// };
+// Then (1 + x)^(1/3) ~ 1 + x * P(x).
+// For example: for 0 <= x <= 1/8:
+// P(x) = 0x1.555556p-2 + x * (-0x1.c71d38p-4 + x * (0x1.f9b95ap-5 + x *
+// (-0x1.4ebe18p-5 + x * 0x1.9ca9d2p-6)))
+
+constexpr float COEFFS[16][5] = {
+ {0x1.555556p-2f, -0x1.c71ea4p-4f, 0x1.faa5f2p-5f, -0x1.64febep-5f,
+ 0x1.733a46p-5f},
+ {0x1.55554ep-2f, -0x1.c715f6p-4f, 0x1.f88a9ep-5f, -0x1.4456e8p-5f,
+ 0x1.5b5ef2p-6f},
+ {0x1.555508p-2f, -0x1.c6f404p-4f, 0x1.f56b7ap-5f, -0x1.33cff8p-5f,
+ 0x1.18f146p-6f},
+ {0x1.5553fcp-2f, -0x1.c69bacp-4f, 0x1.efed98p-5f, -0x1.204706p-5f,
+ 0x1.c90976p-7f},
+ {0x1.55517p-2f, -0x1.c5f996p-4f, 0x1.e85932p-5f, -0x1.0c0c0ep-5f,
+ 0x1.77c766p-7f},
+ {0x1.554c96p-2f, -0x1.c501d2p-4f, 0x1.df0fc4p-5f, -0x1.f067f2p-6f,
+ 0x1.380ab8p-7f},
+ {0x1.55448cp-2f, -0x1.c3ab1ep-4f, 0x1.d45876p-5f, -0x1.ca3988p-6f,
+ 0x1.04f38ap-7f},
+ {0x1.5538aap-2f, -0x1.c1f886p-4f, 0x1.c8b11p-5f, -0x1.a6a16cp-6f,
+ 0x1.b847c2p-8f},
+ {0x1.55278ap-2f, -0x1.bfd538p-4f, 0x1.bbde6p-5f, -0x1.846a8cp-6f,
+ 0x1.73bfcp-8f},
+ {0x1.5511dp-2f, -0x1.bd6c88p-4f, 0x1.af0a3ap-5f, -0x1.660852p-6f,
+ 0x1.3dbe34p-8f},
+ {0x1.54f82ap-2f, -0x1.bada56p-4f, 0x1.a2aa0ep-5f, -0x1.4b8c2ap-6f,
+ 0x1.13379cp-8f},
+ {0x1.54d512p-2f, -0x1.b7a936p-4f, 0x1.94b91ep-5f, -0x1.30792cp-6f,
+ 0x1.d7883cp-9f},
+ {0x1.54a8d8p-2f, -0x1.b3fde2p-4f, 0x1.861aeep-5f, -0x1.169484p-6f,
+ 0x1.92b4cap-9f},
+ {0x1.548126p-2f, -0x1.b0f4a8p-4f, 0x1.7af574p-5f, -0x1.04644ep-6f,
+ 0x1.662fb6p-9f},
+ {0x1.544b9p-2f, -0x1.ad2124p-4f, 0x1.6dd75p-5f, -0x1.e0cbecp-7f,
+ 0x1.387692p-9f},
+ {0x1.5422c6p-2f, -0x1.aa61bp-4f, 0x1.64f4bap-5f, -0x1.c742b2p-7f,
+ 0x1.1cf15ap-9f},
+};
+
+} // anonymous namespace
+
+LLVM_LIBC_FUNCTION(float16, cbrtf16, (float16 x)) {
+ using FPBits = fputil::FPBits<float16>;
+ using FloatBits = fputil::FPBits<float>;
+
+ FPBits x_bits(x);
+
+ uint16_t x_u = x_bits.uintval();
+ uint16_t x_abs = x_u & 0x7fff;
+ uint32_t sign_bit = (x_u >> 15) << FloatBits::EXP_LEN;
+
+ // cbrtf16(0) = 0, cbrtf16(NaN) = NaN
+ if (LIBC_UNLIKELY(x_abs == 0 || x_abs >= 0x7C00)) {
+ if (x_bits.is_signaling_nan()) {
+ fputil::raise_except(FE_INVALID);
+ return FPBits::quiet_nan().uintval();
+ }
+ return x;
+ }
+
+ float xf = static_cast<float>(x);
+ FloatBits xf_bits(xf);
+
+ unsigned x_e = static_cast<unsigned>(xf_bits.get_exponent());
+ unsigned out_e = (x_e / 3 + 127) | sign_bit;
+
+ unsigned shift_e = x_e % 3;
+
+ // Set x_m = 2^(x_e % 3) * (1 + mantissa)
+ uint32_t x_m = xf_bits.get_mantissa();
+
+ // Use the leading 4 bits for look up table
+ unsigned idx = static_cast<unsigned>(x_m >> (FloatBits::FRACTION_LEN - 4));
+
+ x_m |= static_cast<uint32_t>(FloatBits::EXP_BIAS) << FloatBits::FRACTION_LEN;
+
+ float x_reduced = FloatBits(x_m).get_val();
+ float dx = x_reduced - 1.0f;
+
+ float dx_sq = dx * dx;
+
+ // fputil::multiply_add(x, y, z) = x*y + z
+
+ // c0 = 1 + x * a0
+ float c0 = fputil::multiply_add(dx, COEFFS[idx][0], 1.0f);
+ // c1 = a1 + x * a2
+ float c1 = fputil::multiply_add(dx, COEFFS[idx][2], COEFFS[idx][1]);
+ // c2 = a3 + x * a4
+ float c2 = fputil::multiply_add(dx, COEFFS[idx][4], COEFFS[idx][3]);
+ // we save a multiply_add operation by decreasing the polynomial degree by 2
+ // i.e. using a degree-4 polynomial instead of degree 6.
+
+ float dx_4 = dx_sq * dx_sq;
+
+ // p0 = c0 + x^2 * c1
+ // p0 = (1 + x * a0) + x^2 * (a1 + x * a2)
+ // p0 = 1 + x * a0 + x^2 * a1 + x^3 * a2
+ float p0 = fputil::multiply_add(dx_sq, c1, c0);
+
+ // p1 = c2
+ // p1 = x * a4
+ float p1 = c2;
+
+ // r = p0 + x^4 * p1
+ // r = (1 + x * a0 + x^2 * a1 + x^3 * a2) + x^4 (x * a4)
+ // r = 1 + x * a0 + x^2 * a1 + x^3 * a2 + x^5 * a4
+ // r = 1 + x * (a0 + a1 * x + a2 * x^2 + a3 * x^3 + a4 * x^4)
+ // r = 1 + x * P(x)
+ float r = fputil::multiply_add(dx_4, p1, p0) * CBRT2[shift_e];
+
+ uint32_t r_m = FloatBits(r).get_mantissa();
+ // For float, mantissa is 23 bits (instead of 52 for double)
+ // Check if the output is exact. To be exact, the smallest 1-bit of the
+ // output has to be at least 2^-7 or higher. So we check the lowest 15 bits
+ // to see if they are within 2^(-23 + 3) errors from all zeros, then the
+ // result cube root is exact.
+ if (LIBC_UNLIKELY(((r_m + 4) & 0x7fff) <= 8)) {
+ if ((r_m & 0x7fff) <= 4)
+ r_m &= 0xffff'ffe0;
+ else
+ r_m = (r_m & 0xffff'ffe0) + 0x20; // Round up to next multiple of 0x20
+ fputil::clear_except_if_required(FE_INEXACT);
+ }
+
+ uint32_t r_bits =
+ r_m | (static_cast<uint32_t>(out_e) << FloatBits::FRACTION_LEN);
+
+ return static_cast<float16>(FloatBits(r_bits).get_val());
+}
+
+} // namespace LIBC_NAMESPACE_DECL
>From 888ada74207024466b1c402f767d02cd91962227 Mon Sep 17 00:00:00 2001
From: krishna2803 <kpandey81930 at gmail.com>
Date: Sat, 22 Mar 2025 04:23:44 +0530
Subject: [PATCH 03/16] chore: update CMakeLists.txt
Signed-off-by: krishna2803 <kpandey81930 at gmail.com>
---
libc/src/math/CMakeLists.txt | 1 +
libc/src/math/generic/CMakeLists.txt | 18 ++++++++++++++++++
2 files changed, 19 insertions(+)
diff --git a/libc/src/math/CMakeLists.txt b/libc/src/math/CMakeLists.txt
index f18a73d46f9aa..7bcf4ee294126 100644
--- a/libc/src/math/CMakeLists.txt
+++ b/libc/src/math/CMakeLists.txt
@@ -78,6 +78,7 @@ add_math_entrypoint_object(iscanonicalf128)
add_math_entrypoint_object(cbrt)
add_math_entrypoint_object(cbrtf)
+add_math_entrypoint_object(cbrtf16)
add_math_entrypoint_object(ceil)
add_math_entrypoint_object(ceilf)
diff --git a/libc/src/math/generic/CMakeLists.txt b/libc/src/math/generic/CMakeLists.txt
index db07bd1a098cc..f88f133d8efdd 100644
--- a/libc/src/math/generic/CMakeLists.txt
+++ b/libc/src/math/generic/CMakeLists.txt
@@ -4816,6 +4816,24 @@ add_entrypoint_object(
libc.src.__support.integer_literals
)
+add_entrypoint_object(
+ cbrtf16
+ SRCS
+ cbrtf16.cpp
+ HDRS
+ ../cbrtf16.h
+ DEPENDS
+ libc.hdr.fenv_macros
+ libc.src.__support.FPUtil.double_double
+ libc.src.__support.FPUtil.dyadic_float
+ libc.src.__support.FPUtil.fenv_impl
+ libc.src.__support.FPUtil.fp_bits
+ libc.src.__support.FPUtil.multiply_add
+ libc.src.__support.FPUtil.polyeval
+ libc.src.__support.macros.optimization
+ libc.src.__support.integer_literals
+)
+
add_entrypoint_object(
dmull
SRCS
>From 7fc5a41f26c4be2b0cf34b1bda845fbdaf2d6196 Mon Sep 17 00:00:00 2001
From: krishna2803 <kpandey81930 at gmail.com>
Date: Sat, 22 Mar 2025 04:23:57 +0530
Subject: [PATCH 04/16] chore: update entrypoints
Signed-off-by: krishna2803 <kpandey81930 at gmail.com>
---
libc/config/gpu/amdgpu/entrypoints.txt | 1 +
libc/config/gpu/nvptx/entrypoints.txt | 1 +
libc/config/linux/aarch64/entrypoints.txt | 1 +
libc/config/linux/x86_64/entrypoints.txt | 1 +
4 files changed, 4 insertions(+)
diff --git a/libc/config/gpu/amdgpu/entrypoints.txt b/libc/config/gpu/amdgpu/entrypoints.txt
index 291d86b4dd587..0a155e68f307d 100644
--- a/libc/config/gpu/amdgpu/entrypoints.txt
+++ b/libc/config/gpu/amdgpu/entrypoints.txt
@@ -520,6 +520,7 @@ if(LIBC_TYPES_HAS_FLOAT16)
list(APPEND TARGET_LIBM_ENTRYPOINTS
# math.h C23 _Float16 entrypoints
libc.src.math.canonicalizef16
+ libc.src.math.cbrtf16
libc.src.math.ceilf16
libc.src.math.copysignf16
libc.src.math.coshf16
diff --git a/libc/config/gpu/nvptx/entrypoints.txt b/libc/config/gpu/nvptx/entrypoints.txt
index 1ea0d9b03b37e..010265bd915cb 100644
--- a/libc/config/gpu/nvptx/entrypoints.txt
+++ b/libc/config/gpu/nvptx/entrypoints.txt
@@ -522,6 +522,7 @@ if(LIBC_TYPES_HAS_FLOAT16)
list(APPEND TARGET_LIBM_ENTRYPOINTS
# math.h C23 _Float16 entrypoints
libc.src.math.canonicalizef16
+ libc.src.math.cbrtf16
libc.src.math.ceilf16
libc.src.math.copysignf16
libc.src.math.coshf16
diff --git a/libc/config/linux/aarch64/entrypoints.txt b/libc/config/linux/aarch64/entrypoints.txt
index 5c4913a658c2f..651bac5b9e79a 100644
--- a/libc/config/linux/aarch64/entrypoints.txt
+++ b/libc/config/linux/aarch64/entrypoints.txt
@@ -646,6 +646,7 @@ if(LIBC_TYPES_HAS_FLOAT16)
list(APPEND TARGET_LIBM_ENTRYPOINTS
# math.h C23 _Float16 entrypoints
libc.src.math.canonicalizef16
+ libc.src.math.cbrtf16
libc.src.math.ceilf16
libc.src.math.copysignf16
libc.src.math.cospif16
diff --git a/libc/config/linux/x86_64/entrypoints.txt b/libc/config/linux/x86_64/entrypoints.txt
index 124b80d03d846..7f22b4a82ce14 100644
--- a/libc/config/linux/x86_64/entrypoints.txt
+++ b/libc/config/linux/x86_64/entrypoints.txt
@@ -660,6 +660,7 @@ if(LIBC_TYPES_HAS_FLOAT16)
libc.src.math.cosf16
libc.src.math.coshf16
libc.src.math.cospif16
+ libc.src.math.cbrtf16
libc.src.math.exp10f16
libc.src.math.exp10m1f16
libc.src.math.exp2f16
>From 974257aa5cc7cd0e024400ba985e40a37a7161a4 Mon Sep 17 00:00:00 2001
From: krishna2803 <kpandey81930 at gmail.com>
Date: Sat, 22 Mar 2025 04:24:15 +0530
Subject: [PATCH 05/16] feat: add tests for cbrtf16
Signed-off-by: krishna2803 <kpandey81930 at gmail.com>
---
libc/test/src/math/cbrtf16_test.cpp | 56 +++++++++++++++++++++++
libc/test/src/math/smoke/cbrtf16_test.cpp | 33 +++++++++++++
2 files changed, 89 insertions(+)
create mode 100644 libc/test/src/math/cbrtf16_test.cpp
create mode 100644 libc/test/src/math/smoke/cbrtf16_test.cpp
diff --git a/libc/test/src/math/cbrtf16_test.cpp b/libc/test/src/math/cbrtf16_test.cpp
new file mode 100644
index 0000000000000..2e2cfc079aeb5
--- /dev/null
+++ b/libc/test/src/math/cbrtf16_test.cpp
@@ -0,0 +1,56 @@
+//===-- Unittests for cbrtf16 ---------------------------------------------===//
+//
+// 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/math_macros.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/math/cbrtf16.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
+#include "utils/MPFRWrapper/MPFRUtils.h"
+
+using LlvmLibcCbrtf16Test = 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(LlvmLibcCbrtf16Test, PositiveRange) {
+ for (uint16_t v = POS_START; v <= POS_STOP; ++v) {
+ float16 x = FPBits(v).get_val();
+ EXPECT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Cbrt, x,
+ LIBC_NAMESPACE::cbrtf16(x), 0.5);
+ }
+}
+
+TEST_F(LlvmLibcCbrtf16Test, NegativeRange) {
+ for (uint16_t v = NEG_START; v <= NEG_STOP; ++v) {
+ float16 x = FPBits(v).get_val();
+ EXPECT_MPFR_MATCH_ALL_ROUNDING(mpfr::Operation::Cbrt, x,
+ LIBC_NAMESPACE::cbrtf16(x), 0.5);
+ }
+}
+
+TEST_F(LlvmLibcCbrtf16Test, SpecialValues) {
+ constexpr uint16_t INPUTS[] = {
+ 0x4a00, 0x4500, 0x4e00, 0x0c00, 0x4940,
+ };
+ for (uint16_t v : INPUTS) {
+ float16 x = FPBits(v).get_val();
+ mpfr::ForceRoundingMode r(mpfr::RoundingMode::Upward);
+ EXPECT_MPFR_MATCH(mpfr::Operation::Cbrt, x, LIBC_NAMESPACE::cbrtf16(x), 0.5,
+ mpfr::RoundingMode::Upward);
+ }
+
+ ASSERT_EQ(1, 1);
+}
diff --git a/libc/test/src/math/smoke/cbrtf16_test.cpp b/libc/test/src/math/smoke/cbrtf16_test.cpp
new file mode 100644
index 0000000000000..7c8a7103273a0
--- /dev/null
+++ b/libc/test/src/math/smoke/cbrtf16_test.cpp
@@ -0,0 +1,33 @@
+//===-- Unittests for cbrtf16 ---------------------------------------------===//
+//
+// 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/cbrtf16.h"
+#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
+
+using LlvmLibcCbrtfTest = LIBC_NAMESPACE::testing::FPTest<float16>;
+
+using LIBC_NAMESPACE::testing::tlog;
+
+TEST_F(LlvmLibcCbrtfTest, SpecialNumbers) {
+ EXPECT_FP_EQ_ALL_ROUNDING(aNaN, LIBC_NAMESPACE::cbrtf16(aNaN));
+ EXPECT_FP_EQ_ALL_ROUNDING(inf, LIBC_NAMESPACE::cbrtf16(inf));
+ EXPECT_FP_EQ_ALL_ROUNDING(neg_inf, LIBC_NAMESPACE::cbrtf16(neg_inf));
+ EXPECT_FP_EQ_ALL_ROUNDING(zero, LIBC_NAMESPACE::cbrtf16(zero));
+ EXPECT_FP_EQ_ALL_ROUNDING(neg_zero, LIBC_NAMESPACE::cbrtf16(neg_zero));
+ EXPECT_FP_EQ_ALL_ROUNDING(1.0f, LIBC_NAMESPACE::cbrtf16(1.0f));
+ EXPECT_FP_EQ_ALL_ROUNDING(-1.0f, LIBC_NAMESPACE::cbrtf16(-1.0f));
+ EXPECT_FP_EQ_ALL_ROUNDING(2.0f, LIBC_NAMESPACE::cbrtf16(8.0f));
+ EXPECT_FP_EQ_ALL_ROUNDING(-2.0f, LIBC_NAMESPACE::cbrtf16(-8.0f));
+ EXPECT_FP_EQ_ALL_ROUNDING(3.0f, LIBC_NAMESPACE::cbrtf16(27.0f));
+ EXPECT_FP_EQ_ALL_ROUNDING(-3.0f, LIBC_NAMESPACE::cbrtf16(-27.0f));
+ EXPECT_FP_EQ_ALL_ROUNDING(5.0f, LIBC_NAMESPACE::cbrtf16(125.0f));
+ EXPECT_FP_EQ_ALL_ROUNDING(-5.0f, LIBC_NAMESPACE::cbrtf16(-125.0f));
+ EXPECT_FP_EQ_ALL_ROUNDING(40.0f, LIBC_NAMESPACE::cbrtf16(0x1.f4p15));
+ EXPECT_FP_EQ_ALL_ROUNDING(-40.0f, LIBC_NAMESPACE::cbrtf16(-0x1.f4p15));
+}
>From 36d343bd35cfbdea50ac191d4060b2e30c74c1f9 Mon Sep 17 00:00:00 2001
From: krishna2803 <kpandey81930 at gmail.com>
Date: Sat, 22 Mar 2025 04:24:48 +0530
Subject: [PATCH 06/16] chore: update CMakeLists.txt for tests
Signed-off-by: krishna2803 <kpandey81930 at gmail.com>
---
libc/test/src/math/CMakeLists.txt | 12 ++++++++++++
libc/test/src/math/smoke/CMakeLists.txt | 10 ++++++++++
2 files changed, 22 insertions(+)
diff --git a/libc/test/src/math/CMakeLists.txt b/libc/test/src/math/CMakeLists.txt
index beafa87e03a77..1fb7f47b1d541 100644
--- a/libc/test/src/math/CMakeLists.txt
+++ b/libc/test/src/math/CMakeLists.txt
@@ -2655,6 +2655,18 @@ add_fp_unittest(
libc.src.__support.FPUtil.fp_bits
)
+add_fp_unittest(
+ cbrtf16_test
+ NEED_MPFR
+ SUITE
+ libc-math-unittests
+ SRCS
+ cbrtf16_test.cpp
+ DEPENDS
+ libc.src.math.cbrtf16
+ libc.src.__support.FPUtil.fp_bits
+)
+
add_fp_unittest(
dmull_test
NEED_MPFR
diff --git a/libc/test/src/math/smoke/CMakeLists.txt b/libc/test/src/math/smoke/CMakeLists.txt
index 94ec099ddfcbc..f7311d4f2080c 100644
--- a/libc/test/src/math/smoke/CMakeLists.txt
+++ b/libc/test/src/math/smoke/CMakeLists.txt
@@ -5042,6 +5042,16 @@ add_fp_unittest(
libc.src.math.cbrt
)
+add_fp_unittest(
+ cbrtf16_test
+ SUITE
+ libc-math-smoke-tests
+ SRCS
+ cbrtf16_test.cpp
+ DEPENDS
+ libc.src.math.cbrtf16
+)
+
add_fp_unittest(
dmull_test
SUITE
>From 08900aab172dbb42f7d49eedaf4be09ae5a69a40 Mon Sep 17 00:00:00 2001
From: krishna2803 <kpandey81930 at gmail.com>
Date: Sat, 22 Mar 2025 04:30:26 +0530
Subject: [PATCH 07/16] chore: remove debugging artefact.
Signed-off-by: krishna2803 <kpandey81930 at gmail.com>
---
libc/test/src/math/cbrtf16_test.cpp | 2 --
1 file changed, 2 deletions(-)
diff --git a/libc/test/src/math/cbrtf16_test.cpp b/libc/test/src/math/cbrtf16_test.cpp
index 2e2cfc079aeb5..eb55234f053bd 100644
--- a/libc/test/src/math/cbrtf16_test.cpp
+++ b/libc/test/src/math/cbrtf16_test.cpp
@@ -51,6 +51,4 @@ TEST_F(LlvmLibcCbrtf16Test, SpecialValues) {
EXPECT_MPFR_MATCH(mpfr::Operation::Cbrt, x, LIBC_NAMESPACE::cbrtf16(x), 0.5,
mpfr::RoundingMode::Upward);
}
-
- ASSERT_EQ(1, 1);
}
>From ebdaeac6d0e0663c1867aa80b829a859a974c40c Mon Sep 17 00:00:00 2001
From: krishna2803 <kpandey81930 at gmail.com>
Date: Sat, 22 Mar 2025 05:51:01 +0530
Subject: [PATCH 08/16] refactor: separate sign_bit from out_e
Signed-off-by: krishna2803 <kpandey81930 at gmail.com>
---
libc/src/math/generic/cbrtf16.cpp | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/libc/src/math/generic/cbrtf16.cpp b/libc/src/math/generic/cbrtf16.cpp
index 782f1bfd1b100..4757eda2da530 100644
--- a/libc/src/math/generic/cbrtf16.cpp
+++ b/libc/src/math/generic/cbrtf16.cpp
@@ -95,7 +95,7 @@ LLVM_LIBC_FUNCTION(float16, cbrtf16, (float16 x)) {
FloatBits xf_bits(xf);
unsigned x_e = static_cast<unsigned>(xf_bits.get_exponent());
- unsigned out_e = (x_e / 3 + 127) | sign_bit;
+ unsigned out_e = x_e / 3 + 127;
unsigned shift_e = x_e % 3;
@@ -155,8 +155,8 @@ LLVM_LIBC_FUNCTION(float16, cbrtf16, (float16 x)) {
fputil::clear_except_if_required(FE_INEXACT);
}
- uint32_t r_bits =
- r_m | (static_cast<uint32_t>(out_e) << FloatBits::FRACTION_LEN);
+ uint32_t r_bits = r_m | (static_cast<uint32_t>(out_e | sign_bit)
+ << FloatBits::FRACTION_LEN);
return static_cast<float16>(FloatBits(r_bits).get_val());
}
>From a1abd76e6ab808fb3c20042446fe13320534df96 Mon Sep 17 00:00:00 2001
From: krishna2803 <kpandey81930 at gmail.com>
Date: Sat, 22 Mar 2025 06:20:56 +0530
Subject: [PATCH 09/16] chore: fix typo `sqrt` -> `cbrt`
---
libc/src/math/generic/cbrtf16.cpp | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/libc/src/math/generic/cbrtf16.cpp b/libc/src/math/generic/cbrtf16.cpp
index 4757eda2da530..e0382e8c1a9f3 100644
--- a/libc/src/math/generic/cbrtf16.cpp
+++ b/libc/src/math/generic/cbrtf16.cpp
@@ -1,4 +1,4 @@
-//===-- Implementation of sqrtf16 function --------------------------------===//
+//===-- Implementation of cbrtf16 function --------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
>From 089c0a14a54a6123c1a52d57e6b855664b7f6511 Mon Sep 17 00:00:00 2001
From: krishna2803 <kpandey81930 at gmail.com>
Date: Sat, 22 Mar 2025 19:49:40 +0530
Subject: [PATCH 10/16] chore: add cast to uint32_t
Signed-off-by: krishna2803 <kpandey81930 at gmail.com>
---
libc/src/math/generic/cbrtf16.cpp | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/libc/src/math/generic/cbrtf16.cpp b/libc/src/math/generic/cbrtf16.cpp
index e0382e8c1a9f3..94734177df197 100644
--- a/libc/src/math/generic/cbrtf16.cpp
+++ b/libc/src/math/generic/cbrtf16.cpp
@@ -80,7 +80,7 @@ LLVM_LIBC_FUNCTION(float16, cbrtf16, (float16 x)) {
uint16_t x_u = x_bits.uintval();
uint16_t x_abs = x_u & 0x7fff;
- uint32_t sign_bit = (x_u >> 15) << FloatBits::EXP_LEN;
+ uint32_t sign_bit = static_cast<uint32_t>(x_u >> 15) << FloatBits::EXP_LEN;
// cbrtf16(0) = 0, cbrtf16(NaN) = NaN
if (LIBC_UNLIKELY(x_abs == 0 || x_abs >= 0x7C00)) {
>From 4c9b493a2c7b993e4b742e57d08d6925a866bf5c Mon Sep 17 00:00:00 2001
From: krishna2803 <kpandey81930 at gmail.com>
Date: Sat, 22 Mar 2025 21:20:40 +0530
Subject: [PATCH 11/16] fix: exponent handling (fixed for negative exponents!)
Signed-off-by: krishna2803 <kpandey81930 at gmail.com>
---
libc/src/math/generic/cbrtf16.cpp | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)
diff --git a/libc/src/math/generic/cbrtf16.cpp b/libc/src/math/generic/cbrtf16.cpp
index 94734177df197..e715e3d52ef6e 100644
--- a/libc/src/math/generic/cbrtf16.cpp
+++ b/libc/src/math/generic/cbrtf16.cpp
@@ -94,10 +94,9 @@ LLVM_LIBC_FUNCTION(float16, cbrtf16, (float16 x)) {
float xf = static_cast<float>(x);
FloatBits xf_bits(xf);
- unsigned x_e = static_cast<unsigned>(xf_bits.get_exponent());
- unsigned out_e = x_e / 3 + 127;
-
- unsigned shift_e = x_e % 3;
+ uint32_t x_e = xf_bits.get_biased_exponent();
+ uint32_t out_e = (x_e - 1) / 3 + (127 - 42);
+ uint32_t shift_e = (x_e - 1) % 3;
// Set x_m = 2^(x_e % 3) * (1 + mantissa)
uint32_t x_m = xf_bits.get_mantissa();
>From d7052a7ee48839ed0caf03d7af63932feb1f6030 Mon Sep 17 00:00:00 2001
From: krishna2803 <kpandey81930 at gmail.com>
Date: Sat, 22 Mar 2025 21:21:25 +0530
Subject: [PATCH 12/16] fix: update headers
Signed-off-by: krishna2803 <kpandey81930 at gmail.com>
---
libc/src/math/generic/CMakeLists.txt | 6 ++----
libc/src/math/generic/cbrtf16.cpp | 12 ++++++------
2 files changed, 8 insertions(+), 10 deletions(-)
diff --git a/libc/src/math/generic/CMakeLists.txt b/libc/src/math/generic/CMakeLists.txt
index f88f133d8efdd..9e4c4251add53 100644
--- a/libc/src/math/generic/CMakeLists.txt
+++ b/libc/src/math/generic/CMakeLists.txt
@@ -4824,14 +4824,12 @@ add_entrypoint_object(
../cbrtf16.h
DEPENDS
libc.hdr.fenv_macros
- libc.src.__support.FPUtil.double_double
- libc.src.__support.FPUtil.dyadic_float
libc.src.__support.FPUtil.fenv_impl
libc.src.__support.FPUtil.fp_bits
libc.src.__support.FPUtil.multiply_add
- libc.src.__support.FPUtil.polyeval
+ libc.src.__support.common
+ libc.src.__support.macros.config
libc.src.__support.macros.optimization
- libc.src.__support.integer_literals
)
add_entrypoint_object(
diff --git a/libc/src/math/generic/cbrtf16.cpp b/libc/src/math/generic/cbrtf16.cpp
index e715e3d52ef6e..190d764ff25d3 100644
--- a/libc/src/math/generic/cbrtf16.cpp
+++ b/libc/src/math/generic/cbrtf16.cpp
@@ -7,12 +7,12 @@
//===----------------------------------------------------------------------===//
#include "src/math/cbrtf16.h"
-#include "hdr/fenv_macros.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/config.h"
+#include "hdr/fenv_macros.h" // FE_INVALID, FE_INEXACT
+#include "src/__support/FPUtil/FEnvImpl.h" // fputil::raise_except
+#include "src/__support/FPUtil/FPBits.h" // fputil::FPBits
+#include "src/__support/FPUtil/multiply_add.h" // fputil::multiply_add
+#include "src/__support/common.h" // LLVM_LIBC_FUNCTION
+#include "src/__support/macros/config.h" // LIBC_NAMESPACE_DECL
#include "src/__support/macros/optimization.h" // LIBC_UNLIKELY
namespace LIBC_NAMESPACE_DECL {
>From b761bc9004fca281997ee879766bfb6be2b9d495 Mon Sep 17 00:00:00 2001
From: krishna2803 <kpandey81930 at gmail.com>
Date: Sat, 22 Mar 2025 21:21:38 +0530
Subject: [PATCH 13/16] chore: update docs
Signed-off-by: krishna2803 <kpandey81930 at gmail.com>
---
libc/include/math.yaml | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/libc/include/math.yaml b/libc/include/math.yaml
index fbfc51348411a..9b58b50613a24 100644
--- a/libc/include/math.yaml
+++ b/libc/include/math.yaml
@@ -140,6 +140,12 @@ functions:
return_type: float
arguments:
- type: float
+ - name: cbrtf16
+ standards:
+ - stdc
+ return_type: _Float16
+ arguments:
+ - type: _Float16
- name: ceil
standards:
- stdc
>From 26cbd9695b716d7cd6b572dd01f3fa5bf4cd8bfd Mon Sep 17 00:00:00 2001
From: krishna2803 <kpandey81930 at gmail.com>
Date: Sat, 22 Mar 2025 21:22:48 +0530
Subject: [PATCH 14/16] chore: add better tests for special numbers
Signed-off-by: krishna2803 <kpandey81930 at gmail.com>
---
libc/test/src/math/cbrtf16_test.cpp | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/libc/test/src/math/cbrtf16_test.cpp b/libc/test/src/math/cbrtf16_test.cpp
index eb55234f053bd..ac6ee535fcbb7 100644
--- a/libc/test/src/math/cbrtf16_test.cpp
+++ b/libc/test/src/math/cbrtf16_test.cpp
@@ -43,7 +43,12 @@ TEST_F(LlvmLibcCbrtf16Test, NegativeRange) {
TEST_F(LlvmLibcCbrtf16Test, SpecialValues) {
constexpr uint16_t INPUTS[] = {
- 0x4a00, 0x4500, 0x4e00, 0x0c00, 0x4940,
+ 0x4a00, 0x4500, 0x4e00, 0x4940, 0x0c00,
+ 0x4248, // ~pi
+ 0x7bff, // max positive value
+ 0x3800, // 0.5
+ 0x3bec, // ~0.99
+ 0x3c01, // ~1.01
};
for (uint16_t v : INPUTS) {
float16 x = FPBits(v).get_val();
>From 07dd1fdb88507df0a1a48867176c09aa11f41535 Mon Sep 17 00:00:00 2001
From: krishna2803 <kpandey81930 at gmail.com>
Date: Sat, 22 Mar 2025 21:23:15 +0530
Subject: [PATCH 15/16] chore: update bazel build files
Signed-off-by: krishna2803 <kpandey81930 at gmail.com>
---
utils/bazel/llvm-project-overlay/libc/BUILD.bazel | 12 ++++++++++++
.../libc/test/src/math/BUILD.bazel | 2 ++
.../libc/test/src/math/smoke/BUILD.bazel | 2 ++
3 files changed, 16 insertions(+)
diff --git a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
index 6dd425a9f6b5a..90659b93c0373 100644
--- a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
@@ -2377,6 +2377,18 @@ libc_math_function(
],
)
+libc_math_function(
+ name = "cbrtf16",
+ additional_deps = [
+ ":__support_fputil_fenv_impl",
+ ":__support_fputil_fp_bits",
+ ":__support_fputil_multiply_add",
+ ":__support_macros_optimization",
+ ":__support_macros_config",
+ ":__support_common",
+ ],
+)
+
libc_math_function(name = "ceil")
libc_math_function(name = "ceilf")
diff --git a/utils/bazel/llvm-project-overlay/libc/test/src/math/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/test/src/math/BUILD.bazel
index 23cead18de4c1..42633ff884fb8 100644
--- a/utils/bazel/llvm-project-overlay/libc/test/src/math/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/libc/test/src/math/BUILD.bazel
@@ -592,6 +592,8 @@ math_mpfr_test(
hdrs = ["TruncTest.h"],
)
+math_mpfr_test(name = "cbrtf16")
+
math_mpfr_test(name = "cosf16")
math_mpfr_test(name = "cospif16")
diff --git a/utils/bazel/llvm-project-overlay/libc/test/src/math/smoke/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/test/src/math/smoke/BUILD.bazel
index 3c9b1f8d71408..3082de6828aa0 100644
--- a/utils/bazel/llvm-project-overlay/libc/test/src/math/smoke/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/libc/test/src/math/smoke/BUILD.bazel
@@ -81,6 +81,8 @@ math_test(name = "cbrt")
math_test(name = "cbrtf")
+math_test(name = "cbrtf16")
+
math_test(
name = "ceil",
hdrs = ["CeilTest.h"],
>From 5c365f9b3c2c9d6729b8bab986b62f0f01e28f2f Mon Sep 17 00:00:00 2001
From: krishna2803 <kpandey81930 at gmail.com>
Date: Sun, 23 Mar 2025 16:33:28 +0530
Subject: [PATCH 16/16] chore: add comments explaining the exponent
calculations.
Signed-off-by: krishna2803 <kpandey81930 at gmail.com>
---
libc/src/math/generic/cbrtf16.cpp | 19 ++++++++++++++++---
1 file changed, 16 insertions(+), 3 deletions(-)
diff --git a/libc/src/math/generic/cbrtf16.cpp b/libc/src/math/generic/cbrtf16.cpp
index 190d764ff25d3..a9c1b71b401fb 100644
--- a/libc/src/math/generic/cbrtf16.cpp
+++ b/libc/src/math/generic/cbrtf16.cpp
@@ -94,9 +94,22 @@ LLVM_LIBC_FUNCTION(float16, cbrtf16, (float16 x)) {
float xf = static_cast<float>(x);
FloatBits xf_bits(xf);
- uint32_t x_e = xf_bits.get_biased_exponent();
- uint32_t out_e = (x_e - 1) / 3 + (127 - 42);
- uint32_t shift_e = (x_e - 1) % 3;
+ // for single precision float, x_e_biased = x_e + 127
+ // Since x_e / 3 will round to 0, we will get incorrect
+ // results for x_e < 0 and x mod 3 != 0, so we take x_e_biased
+ // which is always positive.
+ // To calculate the correct biased exponent of the result,
+ // we need to calculate the exponent as:
+ // out_e = floor(x_e / 3) + 127
+ // now, floor((x_e_biased-1) / 3) = floor((x_e + 127 - 1) / 3)
+ // = floor((x_e + 126) / 3)
+ // = floor(x_e/3 + 42)
+ // = floor(x_e/3) + 42
+ // => out_e = (floor((x_e_biased-1) / 3) - 42) + 127
+ // => out_e = (x_e_biased-1) / 3 + (127 - 42);
+ uint32_t x_e_biased = xf_bits.get_biased_exponent();
+ uint32_t out_e = (x_e_biased - 1) / 3 + (127 - 42);
+ uint32_t shift_e = (x_e_biased - 1) % 3;
// Set x_m = 2^(x_e % 3) * (1 + mantissa)
uint32_t x_m = xf_bits.get_mantissa();
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