[libc-commits] [libc] [llvm] [libc][math] Refactor acospif16 implementation to header-only in src/__support/math folder. (PR #148574)
Muhammad Bassiouni via libc-commits
libc-commits at lists.llvm.org
Fri Jul 25 10:10:48 PDT 2025
https://github.com/bassiounix updated https://github.com/llvm/llvm-project/pull/148574
>From 12aba46112c49ee17964a1e6e7d62e5c6f46138a Mon Sep 17 00:00:00 2001
From: bassiounix <muhammad.m.bassiouni at gmail.com>
Date: Fri, 25 Jul 2025 20:05:38 +0300
Subject: [PATCH] [libc][math] Refactor acospif16 implementation to header-only
in src/__support/math folder.
---
libc/shared/math.h | 1 +
libc/shared/math/acospif16.h | 29 ++++
libc/src/__support/math/CMakeLists.txt | 15 ++
libc/src/__support/math/acospif16.h | 147 ++++++++++++++++++
libc/src/math/generic/CMakeLists.txt | 12 +-
libc/src/math/generic/acospif16.cpp | 122 +--------------
libc/test/shared/CMakeLists.txt | 1 +
libc/test/shared/shared_math_test.cpp | 2 +
.../llvm-project-overlay/libc/BUILD.bazel | 23 +++
9 files changed, 223 insertions(+), 129 deletions(-)
create mode 100644 libc/shared/math/acospif16.h
create mode 100644 libc/src/__support/math/acospif16.h
diff --git a/libc/shared/math.h b/libc/shared/math.h
index e3c674c27ffaf..135099a6b728e 100644
--- a/libc/shared/math.h
+++ b/libc/shared/math.h
@@ -16,6 +16,7 @@
#include "math/acosf16.h"
#include "math/acoshf.h"
#include "math/acoshf16.h"
+#include "math/acospif16.h"
#include "math/erff.h"
#include "math/exp.h"
#include "math/exp10.h"
diff --git a/libc/shared/math/acospif16.h b/libc/shared/math/acospif16.h
new file mode 100644
index 0000000000000..38225f2a0f288
--- /dev/null
+++ b/libc/shared/math/acospif16.h
@@ -0,0 +1,29 @@
+//===-- Shared acospif16 function -------------------------------*- 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_SHARED_MATH_ACOSPIF16_H
+#define LLVM_LIBC_SHARED_MATH_ACOSPIF16_H
+
+#include "include/llvm-libc-macros/float16-macros.h"
+
+#ifdef LIBC_TYPES_HAS_FLOAT16
+
+#include "shared/libc_common.h"
+#include "src/__support/math/acospif16.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace shared {
+
+using math::acospif16;
+
+} // namespace shared
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LIBC_TYPES_HAS_FLOAT16
+
+#endif // LLVM_LIBC_SHARED_MATH_ACOSPIF16_H
diff --git a/libc/src/__support/math/CMakeLists.txt b/libc/src/__support/math/CMakeLists.txt
index e6e2d95ace6ec..b951c91d83fb5 100644
--- a/libc/src/__support/math/CMakeLists.txt
+++ b/libc/src/__support/math/CMakeLists.txt
@@ -95,6 +95,21 @@ add_header_library(
libc.src.__support.macros.optimization
)
+add_header_library(
+ acospif16
+ HDRS
+ acospif16.h
+ DEPENDS
+ libc.src.__support.FPUtil.cast
+ 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.FPUtil.sqrt
+ libc.src.__support.macros.optimization
+ libc.src.__support.macros.properties.types
+)
+
add_header_library(
asin_utils
HDRS
diff --git a/libc/src/__support/math/acospif16.h b/libc/src/__support/math/acospif16.h
new file mode 100644
index 0000000000000..5829aed2ca94a
--- /dev/null
+++ b/libc/src/__support/math/acospif16.h
@@ -0,0 +1,147 @@
+//===-- Implementation header for acospif16 ---------------------*- 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___SUPPORT_MATH_ACOSPIF16_H
+#define LLVM_LIBC_SRC___SUPPORT_MATH_ACOSPIF16_H
+
+#include "include/llvm-libc-macros/float16-macros.h"
+
+#ifdef LIBC_TYPES_HAS_FLOAT16
+
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/PolyEval.h"
+#include "src/__support/FPUtil/cast.h"
+#include "src/__support/FPUtil/multiply_add.h"
+#include "src/__support/FPUtil/sqrt.h"
+#include "src/__support/macros/optimization.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace math {
+
+static constexpr float16 acospif16(float16 x) {
+ using FPBits = fputil::FPBits<float16>;
+ FPBits xbits(x);
+
+ uint16_t x_u = xbits.uintval();
+ uint16_t x_abs = x_u & 0x7fff;
+ uint16_t x_sign = x_u >> 15;
+
+ // |x| > 0x1p0, |x| > 1, or x is NaN.
+ if (LIBC_UNLIKELY(x_abs > 0x3c00)) {
+ // acospif16(NaN) = NaN
+ if (xbits.is_nan()) {
+ if (xbits.is_signaling_nan()) {
+ fputil::raise_except_if_required(FE_INVALID);
+ return FPBits::quiet_nan().get_val();
+ }
+
+ return x;
+ }
+
+ // 1 < |x| <= +inf
+ fputil::raise_except_if_required(FE_INVALID);
+ fputil::set_errno_if_required(EDOM);
+
+ return FPBits::quiet_nan().get_val();
+ }
+
+ // |x| == 0x1p0, x is 1 or -1
+ // if x is (-)1, return 1
+ // if x is (+)1, return 0
+ if (LIBC_UNLIKELY(x_abs == 0x3c00))
+ return fputil::cast<float16>(x_sign ? 1.0f : 0.0f);
+
+ float xf = x;
+ float xsq = xf * xf;
+
+ // Degree-6 minimax polynomial coefficients of asin(x) generated by Sollya
+ // with: > P = fpminimax(asin(x)/(pi * x), [|0, 2, 4, 6, 8|], [|SG...|], [0,
+ // 0.5]);
+ constexpr float POLY_COEFFS[5] = {0x1.45f308p-2f, 0x1.b2900cp-5f,
+ 0x1.897e36p-6f, 0x1.9efafcp-7f,
+ 0x1.06d884p-6f};
+ // |x| <= 0x1p-1, |x| <= 0.5
+ if (x_abs <= 0x3800) {
+ // if x is 0, return 0.5
+ if (LIBC_UNLIKELY(x_abs == 0))
+ return fputil::cast<float16>(0.5f);
+
+ // Note that: acos(x) = pi/2 + asin(-x) = pi/2 - asin(x), then
+ // acospi(x) = 0.5 - asin(x)/pi
+ float interm =
+ fputil::polyeval(xsq, POLY_COEFFS[0], POLY_COEFFS[1], POLY_COEFFS[2],
+ POLY_COEFFS[3], POLY_COEFFS[4]);
+
+ return fputil::cast<float16>(fputil::multiply_add(-xf, interm, 0.5f));
+ }
+
+ // When |x| > 0.5, assume that 0.5 < |x| <= 1
+ //
+ // Step-by-step range-reduction proof:
+ // 1: Let y = asin(x), such that, x = sin(y)
+ // 2: From complimentary angle identity:
+ // x = sin(y) = cos(pi/2 - y)
+ // 3: Let z = pi/2 - y, such that x = cos(z)
+ // 4: From double angle formula; cos(2A) = 1 - 2 * sin^2(A):
+ // z = 2A, z/2 = A
+ // cos(z) = 1 - 2 * sin^2(z/2)
+ // 5: Make sin(z/2) subject of the formula:
+ // sin(z/2) = sqrt((1 - cos(z))/2)
+ // 6: Recall [3]; x = cos(z). Therefore:
+ // sin(z/2) = sqrt((1 - x)/2)
+ // 7: Let u = (1 - x)/2
+ // 8: Therefore:
+ // asin(sqrt(u)) = z/2
+ // 2 * asin(sqrt(u)) = z
+ // 9: Recall [3]; z = pi/2 - y. Therefore:
+ // y = pi/2 - z
+ // y = pi/2 - 2 * asin(sqrt(u))
+ // 10: Recall [1], y = asin(x). Therefore:
+ // asin(x) = pi/2 - 2 * asin(sqrt(u))
+ // 11: Recall that: acos(x) = pi/2 + asin(-x) = pi/2 - asin(x)
+ // Therefore:
+ // acos(x) = pi/2 - (pi/2 - 2 * asin(sqrt(u)))
+ // acos(x) = 2 * asin(sqrt(u))
+ // acospi(x) = 2 * (asin(sqrt(u)) / pi)
+ //
+ // THE RANGE REDUCTION, HOW?
+ // 12: Recall [7], u = (1 - x)/2
+ // 13: Since 0.5 < x <= 1, therefore:
+ // 0 <= u <= 0.25 and 0 <= sqrt(u) <= 0.5
+ //
+ // Hence, we can reuse the same [0, 0.5] domain polynomial approximation for
+ // Step [11] as `sqrt(u)` is in range.
+ // When -1 < x <= -0.5, the identity:
+ // acos(x) = pi - acos(-x)
+ // acospi(x) = 1 - acos(-x)/pi
+ // allows us to compute for the negative x value (lhs)
+ // with a positive x value instead (rhs).
+
+ float xf_abs = (xf < 0 ? -xf : xf);
+ float u = fputil::multiply_add(-0.5f, xf_abs, 0.5f);
+ float sqrt_u = fputil::sqrt<float>(u);
+
+ float asin_sqrt_u =
+ sqrt_u * fputil::polyeval(u, POLY_COEFFS[0], POLY_COEFFS[1],
+ POLY_COEFFS[2], POLY_COEFFS[3], POLY_COEFFS[4]);
+
+ // Same as acos(x), but devided the expression with pi
+ return fputil::cast<float16>(
+ x_sign ? fputil::multiply_add(-2.0f, asin_sqrt_u, 1.0f)
+ : 2.0f * asin_sqrt_u);
+}
+
+} // namespace math
+
+} // namespace LIBC_NAMESPACE_DECL
+
+#endif // LIBC_TYPES_HAS_FLOAT16
+
+#endif // LLVM_LIBC_SRC___SUPPORT_MATH_ACOSPIF16_H
diff --git a/libc/src/math/generic/CMakeLists.txt b/libc/src/math/generic/CMakeLists.txt
index a001d99e032d6..4ceef99140b3c 100644
--- a/libc/src/math/generic/CMakeLists.txt
+++ b/libc/src/math/generic/CMakeLists.txt
@@ -4043,16 +4043,8 @@ add_entrypoint_object(
HDRS
../acospif16.h
DEPENDS
- libc.hdr.errno_macros
- libc.hdr.fenv_macros
- libc.src.__support.FPUtil.cast
- 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.FPUtil.sqrt
- libc.src.__support.macros.optimization
- libc.src.__support.macros.properties.types
+ libc.src.__support.math.acospif16
+ libc.src.errno.errno
)
add_header_library(
diff --git a/libc/src/math/generic/acospif16.cpp b/libc/src/math/generic/acospif16.cpp
index bfdf1694e3ba6..09cbd9984d4fa 100644
--- a/libc/src/math/generic/acospif16.cpp
+++ b/libc/src/math/generic/acospif16.cpp
@@ -7,128 +7,12 @@
//===----------------------------------------------------------------------===//
#include "src/math/acospif16.h"
-#include "hdr/errno_macros.h"
-#include "hdr/fenv_macros.h"
-#include "src/__support/FPUtil/FEnvImpl.h"
-#include "src/__support/FPUtil/FPBits.h"
-#include "src/__support/FPUtil/PolyEval.h"
-#include "src/__support/FPUtil/cast.h"
-#include "src/__support/FPUtil/multiply_add.h"
-#include "src/__support/FPUtil/sqrt.h"
-#include "src/__support/macros/optimization.h"
+#include "src/__support/math/acospif16.h"
namespace LIBC_NAMESPACE_DECL {
LLVM_LIBC_FUNCTION(float16, acospif16, (float16 x)) {
- using FPBits = fputil::FPBits<float16>;
- FPBits xbits(x);
-
- uint16_t x_u = xbits.uintval();
- uint16_t x_abs = x_u & 0x7fff;
- uint16_t x_sign = x_u >> 15;
-
- // |x| > 0x1p0, |x| > 1, or x is NaN.
- if (LIBC_UNLIKELY(x_abs > 0x3c00)) {
- // acospif16(NaN) = NaN
- if (xbits.is_nan()) {
- if (xbits.is_signaling_nan()) {
- fputil::raise_except_if_required(FE_INVALID);
- return FPBits::quiet_nan().get_val();
- }
-
- return x;
- }
-
- // 1 < |x| <= +inf
- fputil::raise_except_if_required(FE_INVALID);
- fputil::set_errno_if_required(EDOM);
-
- return FPBits::quiet_nan().get_val();
- }
-
- // |x| == 0x1p0, x is 1 or -1
- // if x is (-)1, return 1
- // if x is (+)1, return 0
- if (LIBC_UNLIKELY(x_abs == 0x3c00))
- return fputil::cast<float16>(x_sign ? 1.0f : 0.0f);
-
- float xf = x;
- float xsq = xf * xf;
-
- // Degree-6 minimax polynomial coefficients of asin(x) generated by Sollya
- // with: > P = fpminimax(asin(x)/(pi * x), [|0, 2, 4, 6, 8|], [|SG...|], [0,
- // 0.5]);
- constexpr float POLY_COEFFS[5] = {0x1.45f308p-2f, 0x1.b2900cp-5f,
- 0x1.897e36p-6f, 0x1.9efafcp-7f,
- 0x1.06d884p-6f};
- // |x| <= 0x1p-1, |x| <= 0.5
- if (x_abs <= 0x3800) {
- // if x is 0, return 0.5
- if (LIBC_UNLIKELY(x_abs == 0))
- return fputil::cast<float16>(0.5f);
-
- // Note that: acos(x) = pi/2 + asin(-x) = pi/2 - asin(x), then
- // acospi(x) = 0.5 - asin(x)/pi
- float interm =
- fputil::polyeval(xsq, POLY_COEFFS[0], POLY_COEFFS[1], POLY_COEFFS[2],
- POLY_COEFFS[3], POLY_COEFFS[4]);
-
- return fputil::cast<float16>(fputil::multiply_add(-xf, interm, 0.5f));
- }
-
- // When |x| > 0.5, assume that 0.5 < |x| <= 1
- //
- // Step-by-step range-reduction proof:
- // 1: Let y = asin(x), such that, x = sin(y)
- // 2: From complimentary angle identity:
- // x = sin(y) = cos(pi/2 - y)
- // 3: Let z = pi/2 - y, such that x = cos(z)
- // 4: From double angle formula; cos(2A) = 1 - 2 * sin^2(A):
- // z = 2A, z/2 = A
- // cos(z) = 1 - 2 * sin^2(z/2)
- // 5: Make sin(z/2) subject of the formula:
- // sin(z/2) = sqrt((1 - cos(z))/2)
- // 6: Recall [3]; x = cos(z). Therefore:
- // sin(z/2) = sqrt((1 - x)/2)
- // 7: Let u = (1 - x)/2
- // 8: Therefore:
- // asin(sqrt(u)) = z/2
- // 2 * asin(sqrt(u)) = z
- // 9: Recall [3]; z = pi/2 - y. Therefore:
- // y = pi/2 - z
- // y = pi/2 - 2 * asin(sqrt(u))
- // 10: Recall [1], y = asin(x). Therefore:
- // asin(x) = pi/2 - 2 * asin(sqrt(u))
- // 11: Recall that: acos(x) = pi/2 + asin(-x) = pi/2 - asin(x)
- // Therefore:
- // acos(x) = pi/2 - (pi/2 - 2 * asin(sqrt(u)))
- // acos(x) = 2 * asin(sqrt(u))
- // acospi(x) = 2 * (asin(sqrt(u)) / pi)
- //
- // THE RANGE REDUCTION, HOW?
- // 12: Recall [7], u = (1 - x)/2
- // 13: Since 0.5 < x <= 1, therefore:
- // 0 <= u <= 0.25 and 0 <= sqrt(u) <= 0.5
- //
- // Hence, we can reuse the same [0, 0.5] domain polynomial approximation for
- // Step [11] as `sqrt(u)` is in range.
- // When -1 < x <= -0.5, the identity:
- // acos(x) = pi - acos(-x)
- // acospi(x) = 1 - acos(-x)/pi
- // allows us to compute for the negative x value (lhs)
- // with a positive x value instead (rhs).
-
- float xf_abs = (xf < 0 ? -xf : xf);
- float u = fputil::multiply_add(-0.5f, xf_abs, 0.5f);
- float sqrt_u = fputil::sqrt<float>(u);
-
- float asin_sqrt_u =
- sqrt_u * fputil::polyeval(u, POLY_COEFFS[0], POLY_COEFFS[1],
- POLY_COEFFS[2], POLY_COEFFS[3], POLY_COEFFS[4]);
-
- // Same as acos(x), but devided the expression with pi
- return fputil::cast<float16>(
- x_sign ? fputil::multiply_add(-2.0f, asin_sqrt_u, 1.0f)
- : 2.0f * asin_sqrt_u);
+ return math::acospif16(x);
}
+
} // namespace LIBC_NAMESPACE_DECL
diff --git a/libc/test/shared/CMakeLists.txt b/libc/test/shared/CMakeLists.txt
index 89b607d7e5cc3..680da9147b27c 100644
--- a/libc/test/shared/CMakeLists.txt
+++ b/libc/test/shared/CMakeLists.txt
@@ -12,6 +12,7 @@ add_fp_unittest(
libc.src.__support.math.acosf16
libc.src.__support.math.acoshf
libc.src.__support.math.acoshf16
+ libc.src.__support.math.acospif16
libc.src.__support.math.erff
libc.src.__support.math.exp
libc.src.__support.math.exp10
diff --git a/libc/test/shared/shared_math_test.cpp b/libc/test/shared/shared_math_test.cpp
index 44e90e4d0e8b7..354fa0d55e4ef 100644
--- a/libc/test/shared/shared_math_test.cpp
+++ b/libc/test/shared/shared_math_test.cpp
@@ -8,6 +8,7 @@
#include "shared/math.h"
#include "test/UnitTest/FPMatcher.h"
+#include "test/UnitTest/Test.h"
#ifdef LIBC_TYPES_HAS_FLOAT16
@@ -15,6 +16,7 @@ TEST(LlvmLibcSharedMathTest, AllFloat16) {
int exponent;
EXPECT_FP_EQ(0x0p+0f16, LIBC_NAMESPACE::shared::acoshf16(1.0f16));
+ EXPECT_FP_EQ(0x0p+0f16, LIBC_NAMESPACE::shared::acospif16(1.0f16));
EXPECT_FP_EQ(0x1p+0f16, LIBC_NAMESPACE::shared::exp10f16(0.0f16));
diff --git a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
index 7eaa45396be71..aed7e4cbbbbf9 100644
--- a/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
+++ b/utils/bazel/llvm-project-overlay/libc/BUILD.bazel
@@ -2184,6 +2184,21 @@ libc_support_library(
],
)
+libc_support_library(
+ name = "__support_math_acospif16",
+ hdrs = ["src/__support/math/acospif16.h"],
+ deps = [
+ ":__support_fputil_cast",
+ ":__support_fputil_fenv_impl",
+ ":__support_fputil_fp_bits",
+ ":__support_fputil_multiply_add",
+ ":__support_fputil_polyeval",
+ ":__support_fputil_sqrt",
+ ":__support_macros_optimization",
+ ":__support_macros_properties_types",
+ ],
+)
+
libc_support_library(
name = "__support_math_asin_utils",
hdrs = ["src/__support/math/asin_utils.h"],
@@ -2735,6 +2750,14 @@ libc_math_function(
],
)
+libc_math_function(
+ name = "acospif16",
+ additional_deps = [
+ ":__support_math_acospif16",
+ ":errno",
+ ],
+)
+
libc_math_function(
name = "asinf",
additional_deps = [
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