[libc-commits] [libc] [libc][math][c23] implement C23 math function `tanpif` (PR #147192)

[via libc-commits]

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@@ -0,0 +1,106 @@
+//===-- Single-precision tanpi 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/tanpif.h"
+#include "sincosf_utils.h"
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/cast.h"
+#include "src/__support/FPUtil/except_value_utils.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 {
+
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+constexpr size_t N_EXCEPTS = 3;
+
+constexpr fputil::ExceptValues<float, N_EXCEPTS> TANPIF_EXCEPTS{{
+    // (input, RZ output, RU offset, RD offset, RN offset)
+    {0x38F26685, 0x39BE6182, 1, 0, 0},
+    {0x3E933802, 0x3FA267DD, 1, 0, 0},
+    {0x3F3663FF, 0xBFA267DD, 0, 1, 0},
+}};
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+
+LLVM_LIBC_FUNCTION(float, tanpif, (float x)) {
+  using FPBits = typename fputil::FPBits<float>;
+  FPBits xbits(x);
+
+  uint32_t x_u = xbits.uintval();
+  uint32_t x_abs = x_u & 0x7fff'ffffU;
+  double xd = static_cast<double>(xbits.get_val());
+
+  // Handle exceptional values
+  if (LIBC_UNLIKELY(x_abs <= 0x3F3663FF)) {
+    if (LIBC_UNLIKELY(x_abs == 0U))
+      return x;
+
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+    bool x_sign = x_u >> 31;
+
+    if (auto r = TANPIF_EXCEPTS.lookup_odd(x_abs, x_sign);
+        LIBC_UNLIKELY(r.has_value()))
+      return r.value();
+#endif // !LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+  }
+
+  // Numbers greater or equal to 2^23 are always integers, or infinity, or NaN
+  if (LIBC_UNLIKELY(x_abs >= 0x4B00'0000)) {
+    // x is inf or NaN.
+    if (LIBC_UNLIKELY(x_abs >= 0x7f80'0000U)) {
+      if (xbits.is_signaling_nan()) {
+        fputil::raise_except_if_required(FE_INVALID);
+        return FPBits::quiet_nan().get_val();
+      }
+
+      if (x_abs == 0x7f80'0000U) {
+        fputil::set_errno_if_required(EDOM);
+        fputil::raise_except_if_required(FE_INVALID);
+      }
+
+      return x + FPBits::quiet_nan().get_val();
+    }
+
+    return FPBits::zero(xbits.sign()).get_val();
+  }
+
+  // Range reduction:
+  // For |x| > 1/32, we perform range reduction as follows:
+  // Find k and y such that:
+  //   x = (k + y) * 1/32
+  //   k is an integer
+  //   |y| < 0.5
+  //
+  // This is done by performing:
+  //   k = round(x * 32)
+  //   y = x * 32 - k
+  //
+  // Once k and y are computed, we then deduce the answer by the formula:
+  // tan(x) = sin(x) / cos(x)
+  //        = (sin_y * cos_k + cos_y * sin_k) / (cos_y * cos_k - sin_y * sin_k)
+  double sin_k, cos_k, sin_y, cosm1_y;
+  sincospif_eval(xd, sin_k, cos_k, sin_y, cosm1_y);
+
+  if (LIBC_UNLIKELY(sin_y == 0 && cos_k == 0)) {
+    fputil::set_errno_if_required(EDOM);
+    fputil::raise_except_if_required(FE_DIVBYZERO);
+
+    int32_t x_mp5_u = static_cast<int32_t>(x - 0.5);
----------------
lntue wrote:

mixed precision.  Use either `0.5f` or `xd`.

https://github.com/llvm/llvm-project/pull/147192