[libc-commits] [libc] [libc][math] Implement an integer-only version of double precision sin and cos with 1 ULP errors. (PR #184752)

[via libc-commits]

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+//===-- Implementation header for sin using integer-only --------*- 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_SIN_INTEGER_EVAL_H
+#define LLVM_LIBC_SRC___SUPPORT_MATH_SIN_INTEGER_EVAL_H
+
+#include "src/__support/CPP/bit.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/PolyEval.h"
+#include "src/__support/FPUtil/multiply_add.h"
+#include "src/__support/big_int.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/optimization.h"
+#include "src/__support/math_extras.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace math {
+
+namespace integer_only {
+
+struct Frac128 : public UInt<128> {
+  using UInt<128>::UInt;
+
+  constexpr Frac128 operator~() const {
+    Frac128 r;
+    r.val[0] = ~val[0];
+    r.val[1] = ~val[1];
+    return r;
+  }
+  constexpr Frac128 operator+(const Frac128 &other) const {
+    UInt<128> r = UInt<128>(*this) + (UInt<128>(other));
+
+    return Frac128(r.val);
+  }
+  constexpr Frac128 operator-(const Frac128 &other) const {
+    UInt<128> r = UInt<128>(*this) - (UInt<128>(other));
+
+    return Frac128(r.val);
+  }
+  constexpr Frac128 operator*(const Frac128 &other) const {
+    UInt<128> r = UInt<128>::quick_mul_hi(UInt<128>(other));
+
+    return Frac128(r.val);
+  }
+};
+
+LIBC_INLINE constexpr double sin(double x) {
+  using FPBits = typename fputil::FPBits<double>;
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lntue wrote:

I'm thinking of moving this class to `src/__support/`, next to `big_int.h` and `uint128.h`.

https://github.com/llvm/llvm-project/pull/184752