[libc-commits] [libc] [libc][math][c23] add sinpi function (PR #129379)

[via libc-commits]

https://github.com/lara254 created https://github.com/llvm/llvm-project/pull/129379

This is the implementation of `sinpi`.

>From b4d31d0b5c0303e25054dcb43fcd1db41684f1c7 Mon Sep 17 00:00:00 2001
From: Job Hernandez <lara2993 at proton.me>
Date: Sat, 1 Mar 2025 03:29:20 -0800
Subject: [PATCH] add draft for sinpi

---
 libc/src/math/generic/sinpi.cpp | 63 +++++++++++++++++++++++++++++++++
 1 file changed, 63 insertions(+)
 create mode 100644 libc/src/math/generic/sinpi.cpp

diff --git a/libc/src/math/generic/sinpi.cpp b/libc/src/math/generic/sinpi.cpp
new file mode 100644
index 0000000000000..69116ced9fbc7
--- /dev/null
+++ b/libc/src/math/generic/sinpi.cpp
@@ -0,0 +1,63 @@
+//===-- double-precision sinpi function ----------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#include "src/math/sinpi.h"
+#include "sincos_eval.h"
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/PolyEval.h"
+#include "src/__support/FPUtil/multiply_add.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/optimization.h" // LIBC_UNLIKELY
+
+namespace LIBC_NAMESPACE_DECL {
+
+LLVM_LIBC_FUNCTION(double, sinpi, (double x)) {
+  using FPBits = typename fputil::FPBits<double>;
+  FPBits xbits(x);
+
+  uint64_t x_u = xbits.uintval();
+  uint64_t x_abs = x_u & 0x7fff'ffffU;
+  long double xd = static_cast<long double>(x);
+
+  if (LIBC_UNLIKELY(x_abs >= 0x7c00)) {
+    if (x_abs == 0x7c00) {
+      fputil::set_errno_if_required(EDOM);
+      fputil::raise_except_if_required(FE_INVALID);
+    }
+    return x + FPBits::quiet_nan().get_val();
+  } else {
+    return FPBits::zero(xbits.sign()).get_val();
+  }
+
+  if (LIBC_UNLIKELY(x_abs <= 0x3d80'0000U)) {
+    if (LIBC_UNLIKELY(x_abs < 0x33CD'01D7U)) {
+      if (LIBC_UNLIKELY(x_abs == 0U)) {
+	return x;
+    }
+      long double xdpi = xd * 0x1.921fb5444d18p1;
+       return  static_cast<double>(xdpi);
+    }
+  long double xsq = xd * xd;
+
+  long double result = fputil::polyeval(xsq,0x1.921fb54442d183f07b2385653d8p1, -0x1.4abbce625bd95cdc955aeed9abcp2, 0x1.466bc6769ddfdb085486c0ff3ep1, -0x1.32d2c4a48bfd71fa9cdf60a0e4p-1,  0x1.502cbd2c72e3168ff209bc7656cp-4);
+
+  return static_cast<double>(xd * result);
+  }
+
+  long double sin_k, cos_k, sin_y, cosm1_y;
+  sincospi_eval(xd, sin_k, cos_k, sin_y, cosm1_y);
+
+  if (LIBC_UNLIKELY(sin_y == 0 && sin_k == 0))
+    return FPBits::zero(xbits.sign()).get_val();
+
+  return static_cast<double>(fputil::multiply_add(
+						  sin_y, cos_k, fputil::multiply_add(cosm1_y, sin_k, sin_k)));
+}
+}