[libc-commits] [libc] [llvm] [libc][math][c23] Add asinbf16 math function (PR #184170)

[Mohamed Emad via libc-commits]

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@@ -0,0 +1,101 @@
+//===-- Implementation header for asinbf16 ----------------------*- 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_ASINBF16_H
+#define LLVM_LIBC_SRC___SUPPORT_MATH_ASINBF16_H
+
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/PolyEval.h"
+#include "src/__support/FPUtil/bfloat16.h"
+#include "src/__support/FPUtil/cast.h"
+#include "src/__support/FPUtil/multiply_add.h"
+#include "src/__support/FPUtil/sqrt.h"
+#include "src/__support/macros/optimization.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace math {
+
+LIBC_INLINE constexpr bfloat16 asinbf16(bfloat16 x) {
+  // Generated by Sollya using the following command:
+  // > display = hexadecimal;
+  // > round(pi/2, SG, RN);
+  constexpr float PI_2 = 0x1.921fb6p0f;
+
+  using FPBits = fputil::FPBits<bfloat16>;
+  FPBits xbits(x);
+
+  uint16_t x_u = xbits.uintval();
+  uint16_t x_abs = x_u & 0x7fff;
+  float x_sign = (xbits.sign() == Sign::NEG) ? -1 : 1;
+  float xf = x;
+
+  // case 1: |x|>=1, NaN or Inf
+  if (LIBC_UNLIKELY(x_abs >= 0x3F80)) {
+    if (x_abs == 0x3F80) {
+      return bfloat16(x_sign * PI_2);
+    }
+    // NaN
+    if (xbits.is_nan()) {
+      if (xbits.is_signaling_nan()) {
+        fputil::raise_except_if_required(FE_INVALID);
+        return FPBits::quiet_nan().get_val();
+      }
+      return x; // quiet NaN
+    }
+    // |x|>1 & inf
+    fputil::raise_except_if_required(FE_INVALID);
+    fputil::set_errno_if_required(EDOM); // Domain is bounded
+    return FPBits::quiet_nan().get_val();
+  }
+
+  // case 2:  |x| = {0}
+  if (LIBC_UNLIKELY(x_abs == 0))
+    return x; // with sign
+
+  if (LIBC_UNLIKELY(x_abs <= 0x3D00)) {
+    int rounding = fputil::quick_get_round();
+    if ((xbits.is_pos() && rounding == FE_UPWARD) ||
+        (xbits.is_neg() && rounding == FE_DOWNWARD)) {
+      return bfloat16(fputil::multiply_add(xf, 0x1.0p-13f, xf));
+    }
+    return x;
+  }
+
+  float xf_abs = (xf < 0 ? -xf : xf);
+  float x_sq = xf_abs * xf_abs;
+
+  // Degree 6 polynomial of asin(x) generated using Sollya with command :
+  // > display = hexadecimal
+  // > P = fpminimax(asin(x)/x, [|0,2,4,6|], [|SG,SG,SG,SG|], [0, 0.5]);
+  auto asin_poly = [](float u) {
----------------
hulxv wrote:

use [`asin_eval`](https://github.com/llvm/llvm-project/blob/c782e2d40572ce4ff3a71562265bf6f01857c132/libc/src/__support/math/inv_trigf_utils.h#L171) from `inv_tragf_utils` 

https://github.com/llvm/llvm-project/pull/184170