[libc-commits] [libc] [llvm] [libc][math] Add tgammabf16 math support for bfloat16. (PR #208689)

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+//===-- Implementation header for tgammabf16 --------------------*- 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_TGAMMABF16_H
+#define LLVM_LIBC_SRC___SUPPORT_MATH_TGAMMABF16_H
+
+#include "hdr/errno_macros.h"
+#include "hdr/fenv_macros.h"
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/bfloat16.h"
+#include "src/__support/FPUtil/cast.h"
+#include "src/__support/FPUtil/multiply_add.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/optimization.h"
+#include "src/__support/math/exp.h"
+#include "src/__support/math/log.h"
+#include "src/__support/math/sin.h"
+
+namespace LIBC_NAMESPACE_DECL {
+namespace math {
+
+namespace tgammabf16_internal {
+
+LIBC_INLINE_VAR constexpr double PI = 0x1.921fb54442d18p+1;
+LIBC_INLINE_VAR constexpr double LOG_SQRT_2_PI = 0x1.d67f1c864beb5p-1;
+
+// Paul Godfrey's exact Lanczos approximation coefficients (g=7, n=9)
+LIBC_INLINE_VAR constexpr double LANCZOS_COEFFS[9] = {
+    0.99999999999980993,  676.5203681218851,     -1259.1392167224028,
+    771.32342877765313,   -176.61502916214059,   12.507343278224757,
+    -0.13857109526572012, 9.9843695780195716e-6, 1.5056327351493116e-7};
+
+LIBC_INLINE bool is_negative_integer(double x) {
+  if (x > -1.0)
+    return false;
+  if (x <= -128.0)
+    return true;
+  int n = static_cast<int>(x);
+  return x == static_cast<double>(n);
+}
+
+} // namespace tgammabf16_internal
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Sukumarsawant wrote:

you can shift this inside the function unless its used or plan to be used somewhere else .
Also can we do it in `float`(or lesser) instead of `double` in this folder ?

https://github.com/llvm/llvm-project/pull/208689