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[libc][stdfix] Implement fxdivi functions
Signed-off-by: Shreeyash Pandey <[email protected]>
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‎libc/config/linux/riscv/entrypoints.txt‎

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@@ -986,6 +986,7 @@ if(LIBC_COMPILER_HAS_FIXED_POINT)
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libc.src.stdfix.idivulr
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libc.src.stdfix.idivuk
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libc.src.stdfix.idivulk
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libc.src.stdfix.rdivi
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)
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endif()
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‎libc/config/linux/x86_64/entrypoints.txt‎

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@@ -1019,6 +1019,7 @@ if(LIBC_COMPILER_HAS_FIXED_POINT)
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libc.src.stdfix.idivulr
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libc.src.stdfix.idivuk
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libc.src.stdfix.idivulk
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libc.src.stdfix.rdivi
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)
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endif()
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‎libc/include/stdfix.yaml‎

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@@ -544,3 +544,11 @@ functions:
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arguments:
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- type: unsigned long accum
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guard: LIBC_COMPILER_HAS_FIXED_POINT
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- name: rdivi
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standards:
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- stdc_ext
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return_type: fract
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arguments:
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- type: int
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- type: int
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guard: LIBC_COMPILER_HAS_FIXED_POINT

‎libc/src/__support/fixed_point/fx_bits.h‎

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@@ -224,6 +224,59 @@ idiv(T x, T y) {
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return static_cast<XType>(result);
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}
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LIBC_INLINE long accum nrstep(long accum d, long accum x0) {
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auto v = x0 * (2.lk - (d * x0));
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return v;
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}
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/* Divide the two integers and return a fixed_point value
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*
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* For reference, see:
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* https://en.wikipedia.org/wiki/Division_algorithm#Newton%E2%80%93Raphson_division
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* https://stackoverflow.com/a/9231996
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*/
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template <typename XType> LIBC_INLINE constexpr XType divi(int n, int d) {
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// If the value of the second operand of the / operator is zero, the
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// behavior is undefined. Ref: ISO/IEC TR 18037:2008(E) p.g. 16
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LIBC_CRASH_ON_VALUE(d, 0);
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if (LIBC_UNLIKELY(n == 0)) {
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return FXRep<XType>::ZERO();
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}
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bool d_is_signed = false;
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if (d < 0) {
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d = (d * -1);
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d_is_signed = true;
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}
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unsigned int nv = static_cast<unsigned int>(n);
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unsigned int dv = static_cast<unsigned int>(d);
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unsigned int clz = cpp::countl_zero<unsigned int>(dv) - 1;
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unsigned long int scaled_val = dv << clz;
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/* Scale denominator to be in the range of [0.5,1] */
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FXBits<long accum> d_scaled{scaled_val};
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unsigned long int scaled_val_n = nv << clz;
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/* Scale the numerator as much as the denominator to maintain correctness of
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* the original equation
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*/
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FXBits<long accum> n_scaled{scaled_val_n};
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long accum n_scaled_val = n_scaled.get_val();
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long accum d_scaled_val = d_scaled.get_val();
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/* x0 = (48/17) - (32/17) * d_n */
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long accum a = 2.8235lk; /* 48/17 */
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long accum b = 1.8823lk; /* 32/17 */
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long accum initial_approx = a - (b * d_scaled_val);
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long accum val = nrstep(d_scaled_val, initial_approx);
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val = nrstep(d_scaled_val, val);
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val = nrstep(d_scaled_val, val);
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val = nrstep(d_scaled_val, val);
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long accum res = n_scaled_val * val;
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if (d_is_signed) {
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res *= static_cast<XType>(-1);
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}
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return static_cast<XType>(res);
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}
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} // namespace fixed_point
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} // namespace LIBC_NAMESPACE_DECL
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‎libc/src/stdfix/CMakeLists.txt‎

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@@ -89,6 +89,20 @@ foreach(suffix IN ITEMS r lr k lk ur ulr uk ulk)
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)
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endforeach()
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foreach(suffix IN ITEMS r)
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add_entrypoint_object(
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${suffix}divi
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HDRS
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${suffix}divi.h
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SRCS
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${suffix}divi.cpp
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COMPILE_OPTIONS
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${libc_opt_high_flag}
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DEPENDS
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libc.src.__support.fixed_point.fx_bits
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)
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endforeach()
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add_entrypoint_object(
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uhksqrtus
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HDRS

‎libc/src/stdfix/rdivi.cpp‎

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//===-- Implementation of rdivi function ---------------------------------===//
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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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#include "rdivi.h"
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#include "include/llvm-libc-macros/stdfix-macros.h" // fract
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#include "src/__support/common.h" // LLVM_LIBC_FUNCTION
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#include "src/__support/fixed_point/fx_bits.h" // fixed_point
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#include "src/__support/macros/config.h" // LIBC_NAMESPACE_DECL
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namespace LIBC_NAMESPACE_DECL {
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LLVM_LIBC_FUNCTION(fract, rdivi, (int a, int b)) {
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return fixed_point::divi<fract>(a,b);
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}
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} // namespace LIBC_NAMESPACE_DECL

‎libc/src/stdfix/rdivi.h‎

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//===-- Implementation header for rdivi ------------------------*- 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_STDFIX_RDIVI_H
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#define LLVM_LIBC_SRC_STDFIX_RDIVI_H
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#include "include/llvm-libc-macros/stdfix-macros.h"
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#include "src/__support/macros/config.h"
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namespace LIBC_NAMESPACE_DECL {
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fract rdivi(int a, int b);
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} // namespace LIBC_NAMESPACE_DECL
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#endif // LLVM_LIBC_SRC_STDFIX_RDIVI_H

‎libc/test/src/stdfix/CMakeLists.txt‎

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@@ -120,6 +120,22 @@ foreach(suffix IN ITEMS r lr k lk ur ulr uk ulk)
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)
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endforeach()
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foreach(suffix IN ITEMS r)
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add_libc_test(
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${suffix}divi_test
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SUITE
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libc-stdfix-tests
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HDRS
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DivITest.h
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SRCS
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${suffix}divi_test.cpp
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DEPENDS
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libc.src.stdfix.${suffix}divi
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libc.src.__support.fixed_point.fx_bits
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libc.hdr.signal_macros
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)
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endforeach()
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add_libc_test(
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uhksqrtus_test
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SUITE

‎libc/test/src/stdfix/DivITest.h‎

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//===-- Utility class to test fxdivi functions ------------------*- 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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#include "src/__support/CPP/type_traits.h"
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#include "src/__support/fixed_point/fx_bits.h"
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#include "src/__support/fixed_point/fx_rep.h"
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#include "test/UnitTest/Test.h"
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template <typename XType> XType get_epsilon() {
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// TODO: raise error
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return 0;
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}
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template <> fract get_epsilon() { return FRACT_EPSILON; }
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template <> unsigned fract get_epsilon() { return UFRACT_EPSILON; }
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template <> long fract get_epsilon() { return LFRACT_EPSILON; }
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template <typename XType>
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class DivITest : public LIBC_NAMESPACE::testing::Test {
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using FXRep = LIBC_NAMESPACE::fixed_point::FXRep<XType>;
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using FXBits = LIBC_NAMESPACE::fixed_point::FXBits<XType>;
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public:
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typedef XType (*DivIFunc)(int, int);
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void testBasic(DivIFunc func) {
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XType epsilon = get_epsilon<XType>();
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EXPECT_LT((func(2, 3) - 0.666666r), epsilon);
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EXPECT_LT((func(3, 4) - 0.75r), epsilon);
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EXPECT_LT((func(1043, 2764) - 0.37735r), epsilon);
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EXPECT_LT((func(60000, 720293) - 0.083299r), epsilon);
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EXPECT_EQ(func(128, 256), 0.5r);
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EXPECT_EQ(func(1, 2), 0.5r);
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EXPECT_EQ(func(1, 4), 0.25r);
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EXPECT_EQ(func(1, 8), 0.125r);
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EXPECT_EQ(func(1, 16), 0.0625r);
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EXPECT_EQ(func(-1, 2), -0.5r);
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EXPECT_EQ(func(1, -4), -0.25r);
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EXPECT_EQ(func(-1, 8), -0.125r);
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EXPECT_EQ(func(1, -16), -0.0625r);
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}
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void testSpecial(DivIFunc func) {
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EXPECT_EQ(func(0,10), 0.r);
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EXPECT_DEATH([func] { func(10, 0); }, WITH_SIGNAL(-1));
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EXPECT_EQ(func(-32768,32768), FRACT_MIN);
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EXPECT_EQ(func(32767,32768), FRACT_MAX);
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}
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};
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#define LIST_DIVI_TESTS(Name, XType, func) \
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using LlvmLibc##Name##diviTest = DivITest<XType>; \
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TEST_F(LlvmLibc##Name##diviTest, Basic) { testBasic(&func); } \
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TEST_F(LlvmLibc##Name##diviTest, Special) { testSpecial(&func); } \
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static_assert(true, "Require semicolon.")

‎libc/test/src/stdfix/rdivi_test.cpp‎

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//===-- Unittests for rdivi -----------------------------------------------===//
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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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#include "DivITest.h"
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#include "llvm-libc-macros/stdfix-macros.h" // fract
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#include "src/stdfix/rdivi.h"
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LIST_DIVI_TESTS(r, fract, LIBC_NAMESPACE::rdivi);

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