[libc-commits] [libc] [llvm] [libc][math] Refactor tanpif16 to header-only (PR #181240)

[Muhammad Bassiouni via libc-commits]

================
@@ -0,0 +1,122 @@
+//===-- Implementation header for tanpif16 ----------------------*- 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_TANPIF16_H
+#define LLVM_LIBC_SRC___SUPPORT_MATH_TANPIF16_H
+
+#include "include/llvm-libc-macros/float16-macros.h"
+
+#ifdef LIBC_TYPES_HAS_FLOAT16
+
+#include "hdr/errno_macros.h"
+#include "hdr/fenv_macros.h"
+#include "sincosf16_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/macros/optimization.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace math {
+
+LIBC_INLINE float16 tanpif16(float16 x) {
+  using namespace sincosf16_internal;
+  using FPBits = typename fputil::FPBits<float16>;
+  FPBits xbits(x);
+
+  uint16_t x_u = xbits.uintval();
+  uint16_t x_abs = x_u & 0x7fff;
+
+  // Handle exceptional values
+  if (LIBC_UNLIKELY(x_abs <= 0x4335)) {
+    if (LIBC_UNLIKELY(x_abs == 0U))
+      return x;
+
+#ifndef LIBC_MATH_HAS_SKIP_ACCURATE_PASS
+    constexpr size_t N_EXCEPTS = 21;
+
+    constexpr fputil::ExceptValues<float16, N_EXCEPTS> TANPIF16_EXCEPTS{{
+        // (input, RZ output, RU offset, RD offset, RN offset)
+        {0x07f2, 0x0e3d, 1, 0, 0}, {0x086a, 0x0eee, 1, 0, 1},
+        {0x08db, 0x0fa0, 1, 0, 0}, {0x094c, 0x1029, 1, 0, 0},
+        {0x0b10, 0x118c, 1, 0, 0}, {0x1ce0, 0x23a8, 1, 0, 1},
+        {0x1235, 0x18e0, 1, 0, 0}, {0x2579, 0x2c4e, 1, 0, 0},
+        {0x28b2, 0x2f68, 1, 0, 1}, {0x2a43, 0x30f4, 1, 0, 1},
+        {0x31b7, 0x3907, 1, 0, 0}, {0x329d, 0x3a12, 1, 0, 1},
+        {0x34f1, 0x3dd7, 1, 0, 0}, {0x3658, 0x41ee, 1, 0, 0},
+        {0x38d4, 0xc1ee, 0, 1, 0}, {0x3d96, 0x41ee, 1, 0, 0},
+        {0x3e6a, 0xc1ee, 0, 1, 0}, {0x40cb, 0x41ee, 1, 0, 0},
+        {0x4135, 0xc1ee, 0, 1, 0}, {0x42cb, 0x41ee, 1, 0, 0},
+        {0x4335, 0xc1ee, 0, 1, 0},
+    }};
+
+    bool x_sign = x_u >> 15;
+
+    if (auto r = TANPIF16_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 2^10 are integers, or infinity, or NaN
+  if (LIBC_UNLIKELY(x_abs >= 0x6400)) {
+    // Check for NaN or infinity values
+    if (LIBC_UNLIKELY(x_abs >= 0x7c00)) {
+      if (xbits.is_signaling_nan()) {
+        fputil::raise_except_if_required(FE_INVALID);
+        return FPBits::quiet_nan().get_val();
+      }
+      // is inf
+      if (x_abs == 0x7c00) {
+        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)
+  float xf = x;
+  float sin_k = 0, cos_k = 0, sin_y = 0, cosm1_y = 0;
+  sincospif16_eval(xf, 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);
+
+    int16_t x_mp5_u = static_cast<int16_t>(x - 0.5);
+    return ((x_mp5_u & 0x1) ? -1 : 1) * FPBits::inf().get_val();
+  }
+
+  using fputil::multiply_add;
+  return fputil::cast<float16>(
+      multiply_add(sin_y, cos_k, multiply_add(cosm1_y, sin_k, sin_k)) /
+      multiply_add(sin_y, -sin_k, multiply_add(cosm1_y, cos_k, cos_k)));
+}
+} // namespace math
+} // namespace LIBC_NAMESPACE_DECL
----------------
bassiounix wrote:

```suggestion
}

} // namespace math
} // namespace LIBC_NAMESPACE_DECL
```

https://github.com/llvm/llvm-project/pull/181240