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

[Muhammad Bassiouni via libc-commits]

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@@ -0,0 +1,300 @@
+//===-- 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) {
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bassiounix wrote:

It may result in build errors when this merged. This happened to me many times, no complains about constexpr in precommit but once committed it starts complaining.

It should be safe to just remove it right now and add it later once we agree on a way to qualify `constexpr` in math library.

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