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[libc][math] Refactor cosf16 implementation to header-only in src/__support/math folder. (#152871)
Part of #147386 in preparation for: https://discourse.llvm.org/t/rfc-make-clang-builtin-math-functions-constexpr-with-llvm-libc-to-support-c-23-constexpr-math-functions/86450
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15 files changed

+217
-129
lines changed

15 files changed

+217
-129
lines changed

‎libc/shared/math.h

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@@ -34,6 +34,7 @@
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#include "math/cbrtf.h"
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#include "math/cos.h"
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#include "math/cosf.h"
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#include "math/cosf16.h"
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#include "math/erff.h"
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#include "math/exp.h"
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#include "math/exp10.h"

‎libc/shared/math/cosf16.h

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//===-- Shared cosf16 function ----------------------------------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_LIBC_SHARED_MATH_COSF16_H
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#define LLVM_LIBC_SHARED_MATH_COSF16_H
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#include "shared/libc_common.h"
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#ifdef LIBC_TYPES_HAS_FLOAT16
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#include "src/__support/math/cosf16.h"
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namespace LIBC_NAMESPACE_DECL {
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namespace shared {
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using math::cosf16;
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} // namespace shared
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} // namespace LIBC_NAMESPACE_DECL
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#endif // LIBC_TYPES_HAS_FLOAT16
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#endif // LLVM_LIBC_SHARED_MATH_COSF16_H

‎libc/src/__support/math/CMakeLists.txt

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@@ -390,6 +390,23 @@ add_header_library(
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libc.src.__support.macros.optimization
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)
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add_header_library(
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cosf16
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HDRS
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cosf16.h
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DEPENDS
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.sincosf16_utils
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libc.hdr.errno_macros
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libc.hdr.fenv_macros
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libc.src.__support.FPUtil.cast
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libc.src.__support.FPUtil.fenv_impl
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libc.src.__support.FPUtil.fp_bits
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libc.src.__support.FPUtil.except_value_utils
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libc.src.__support.FPUtil.multiply_add
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libc.src.__support.macros.optimization
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libc.src.__support.macros.properties.types
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)
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add_header_library(
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erff
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HDRS
@@ -699,3 +716,13 @@ add_header_library(
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libc.src.__support.FPUtil.polyeval
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libc.src.__support.common
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)
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add_header_library(
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sincosf16_utils
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HDRS
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sincosf16_utils.h
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DEPENDS
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libc.src.__support.FPUtil.polyeval
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libc.src.__support.FPUtil.nearest_integer
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libc.src.__support.common
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)

‎libc/src/__support/math/cosf16.h

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//===-- Implementation header for cosf16 ------------------------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_LIBC_SRC___SUPPORT_MATH_COSF16_H
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#define LLVM_LIBC_SRC___SUPPORT_MATH_COSF16_H
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#include "include/llvm-libc-macros/float16-macros.h"
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#ifdef LIBC_TYPES_HAS_FLOAT16
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#include "sincosf16_utils.h"
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#include "src/__support/FPUtil/FEnvImpl.h"
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#include "src/__support/FPUtil/FPBits.h"
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#include "src/__support/FPUtil/cast.h"
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#include "src/__support/FPUtil/except_value_utils.h"
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#include "src/__support/FPUtil/multiply_add.h"
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#include "src/__support/macros/optimization.h"
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namespace LIBC_NAMESPACE_DECL {
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namespace math {
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LIBC_INLINE static constexpr float16 cosf16(float16 x) {
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#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
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constexpr size_t N_EXCEPTS = 4;
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constexpr fputil::ExceptValues<float16, N_EXCEPTS> COSF16_EXCEPTS{{
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// (input, RZ output, RU offset, RD offset, RN offset)
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{0x2b7c, 0x3bfc, 1, 0, 1},
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{0x4ac1, 0x38b5, 1, 0, 0},
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{0x5c49, 0xb8c6, 0, 1, 0},
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{0x7acc, 0xa474, 0, 1, 0},
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}};
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#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
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using namespace sincosf16_internal;
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using FPBits = fputil::FPBits<float16>;
43+
FPBits xbits(x);
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uint16_t x_u = xbits.uintval();
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uint16_t x_abs = x_u & 0x7fff;
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float xf = x;
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// Range reduction:
50+
// For |x| > pi/32, we perform range reduction as follows:
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// Find k and y such that:
52+
// x = (k + y) * pi/32
53+
// k is an integer, |y| < 0.5
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//
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// This is done by performing:
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// k = round(x * 32/pi)
57+
// y = x * 32/pi - k
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//
59+
// Once k and y are computed, we then deduce the answer by the cosine of sum
60+
// formula:
61+
// cos(x) = cos((k + y) * pi/32)
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// = cos(k * pi/32) * cos(y * pi/32) -
63+
// sin(k * pi/32) * sin(y * pi/32)
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65+
#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
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// Handle exceptional values
67+
if (auto r = COSF16_EXCEPTS.lookup(x_abs); LIBC_UNLIKELY(r.has_value()))
68+
return r.value();
69+
#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
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// cos(+/-0) = 1
72+
if (LIBC_UNLIKELY(x_abs == 0U))
73+
return fputil::cast<float16>(1.0f);
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// cos(+/-inf) = NaN, and cos(NaN) = NaN
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if (xbits.is_inf_or_nan()) {
77+
if (xbits.is_signaling_nan()) {
78+
fputil::raise_except_if_required(FE_INVALID);
79+
return FPBits::quiet_nan().get_val();
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}
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if (xbits.is_inf()) {
83+
fputil::set_errno_if_required(EDOM);
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fputil::raise_except_if_required(FE_INVALID);
85+
}
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return x + FPBits::quiet_nan().get_val();
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}
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float sin_k = 0.0f, cos_k = 0.0f, sin_y = 0.0f, cosm1_y = 0.0f;
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sincosf16_eval(xf, sin_k, cos_k, sin_y, cosm1_y);
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// Since, cosm1_y = cos_y - 1, therefore:
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// cos(x) = cos_k * cos_y - sin_k * sin_y
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// = cos_k * (cos_y - 1 + 1) - sin_k * sin_y
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// = cos_k * cosm1_y - sin_k * sin_y + cos_k
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return fputil::cast<float16>(fputil::multiply_add(
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cos_k, cosm1_y, fputil::multiply_add(-sin_k, sin_y, cos_k)));
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}
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} // namespace math
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} // namespace LIBC_NAMESPACE_DECL
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#endif // LIBC_TYPES_HAS_FLOAT16
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#endif // LLVM_LIBC_SRC___SUPPORT_MATH_COSF16_H

‎libc/src/math/generic/sincosf16_utils.h renamed to ‎libc/src/__support/math/sincosf16_utils.h

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@@ -16,6 +16,8 @@
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namespace LIBC_NAMESPACE_DECL {
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namespace sincosf16_internal {
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// Lookup table for sin(k * pi / 32) with k = 0, ..., 63.
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// Table is generated with Sollya as follows:
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// > display = hexadecimmal;
@@ -66,7 +68,7 @@ LIBC_INLINE int32_t range_reduction_sincosf16(float x, float &y) {
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return static_cast<int32_t>(kd);
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}
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static LIBC_INLINE void sincosf16_poly_eval(int32_t k, float y, float &sin_k,
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LIBC_INLINE static void sincosf16_poly_eval(int32_t k, float y, float &sin_k,
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float &cos_k, float &sin_y,
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float &cosm1_y) {
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@@ -107,6 +109,8 @@ LIBC_INLINE void sincospif16_eval(float xf, float &sin_k, float &cos_k,
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sincosf16_poly_eval(k, y, sin_k, cos_k, sin_y, cosm1_y);
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}
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} // namespace sincosf16_internal
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} // namespace LIBC_NAMESPACE_DECL
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#endif // LLVM_LIBC_SRC_MATH_GENERIC_SINCOSF16_UTILS_H

‎libc/src/math/generic/CMakeLists.txt

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@@ -278,16 +278,6 @@ add_entrypoint_object(
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libc.src.__support.FPUtil.generic.add_sub
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)
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add_header_library(
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sincosf16_utils
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HDRS
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sincosf16_utils.h
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DEPENDS
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libc.src.__support.FPUtil.polyeval
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libc.src.__support.FPUtil.nearest_integer
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libc.src.__support.common
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)
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add_entrypoint_object(
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cos
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SRCS
@@ -315,16 +305,7 @@ add_entrypoint_object(
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HDRS
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../cosf16.h
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DEPENDS
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.sincosf16_utils
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libc.hdr.errno_macros
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libc.hdr.fenv_macros
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libc.src.__support.FPUtil.cast
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libc.src.__support.FPUtil.fenv_impl
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libc.src.__support.FPUtil.fp_bits
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libc.src.__support.FPUtil.except_value_utils
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libc.src.__support.FPUtil.multiply_add
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libc.src.__support.macros.optimization
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libc.src.__support.macros.properties.types
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libc.src.__support.math.cosf16
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)
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add_entrypoint_object(
@@ -349,14 +330,14 @@ add_entrypoint_object(
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HDRS
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../cospif16.h
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DEPENDS
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.sincosf16_utils
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libc.hdr.errno_macros
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libc.hdr.fenv_macros
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libc.src.__support.FPUtil.cast
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libc.src.__support.FPUtil.fenv_impl
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libc.src.__support.FPUtil.fp_bits
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libc.src.__support.FPUtil.multiply_add
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libc.src.__support.macros.optimization
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libc.src.__support.math.sincosf16_utils
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)
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add_entrypoint_object(
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HDRS
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../sinf16.h
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DEPENDS
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.sincosf16_utils
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libc.hdr.errno_macros
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libc.hdr.fenv_macros
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libc.src.__support.FPUtil.cast
@@ -415,6 +395,7 @@ add_entrypoint_object(
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libc.src.__support.FPUtil.multiply_add
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libc.src.__support.macros.optimization
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libc.src.__support.macros.properties.types
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libc.src.__support.math.sincosf16_utils
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COMPILE_OPTIONS
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${libc_opt_high_flag}
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)
@@ -482,14 +463,14 @@ add_entrypoint_object(
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HDRS
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../sinpif16.h
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DEPENDS
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.sincosf16_utils
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libc.hdr.errno_macros
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libc.hdr.fenv_macros
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libc.src.__support.FPUtil.cast
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libc.src.__support.FPUtil.fenv_impl
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libc.src.__support.FPUtil.fp_bits
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libc.src.__support.FPUtil.multiply_add
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libc.src.__support.macros.optimization
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libc.src.__support.math.sincosf16_utils
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)
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add_entrypoint_object(
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HDRS
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../tanf16.h
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DEPENDS
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.sincosf16_utils
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libc.hdr.errno_macros
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libc.hdr.fenv_macros
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libc.src.__support.FPUtil.cast
@@ -548,6 +528,7 @@ add_entrypoint_object(
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libc.src.__support.FPUtil.multiply_add
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libc.src.__support.macros.optimization
550530
libc.src.__support.macros.properties.types
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libc.src.__support.math.sincosf16_utils
551532
)
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add_entrypoint_object(
@@ -572,7 +553,6 @@ add_entrypoint_object(
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HDRS
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../tanpif16.h
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DEPENDS
575-
.sincosf16_utils
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libc.hdr.errno_macros
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libc.hdr.fenv_macros
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libc.src.__support.FPUtil.cast
@@ -581,6 +561,7 @@ add_entrypoint_object(
581561
libc.src.__support.FPUtil.except_value_utils
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libc.src.__support.FPUtil.multiply_add
583563
libc.src.__support.macros.optimization
564+
libc.src.__support.math.sincosf16_utils
584565
)
585566

586567
add_entrypoint_object(

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