libc/src/__support/FPUtil/PolyEval.h

   1 //===-- Common header for PolyEval implementations --------------*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 #ifndef LLVM_LIBC_SRC_SUPPORT_FPUTIL_POLYEVAL_H
  10 #define LLVM_LIBC_SRC_SUPPORT_FPUTIL_POLYEVAL_H
  11
  12 #include "multiply_add.h"
  13 #include "src/__support/common.h"
  14
  15 // Evaluate polynomial using Horner's Scheme:
  16 // With polyeval(x, a_0, a_1, ..., a_n) = a_n * x^n + ... + a_1 * x + a_0, we
  17 // evaluated it as:  a_0 + x * (a_1 + x * ( ... (a_(n-1) + x * a_n) ... ) ) ).
  18 // We will use FMA instructions if available.
  19 // Example: to evaluate x^3 + 2*x^2 + 3*x + 4, call
  20 //   polyeval( x, 4.0, 3.0, 2.0, 1.0 )
  21
  22 namespace __llvm_libc {
  23 namespace fputil {
  24
  25 template <typename T> LIBC_INLINE T polyeval(T, T a0) { return a0; }
  26
  27 template <typename T, typename... Ts>
  28 LIBC_INLINE T polyeval(T x, T a0, Ts... a) {
  29   return multiply_add(x, polyeval(x, a...), a0);
  30 }
  31
  32 } // namespace fputil
  33 } // namespace __llvm_libc
  34
  35 #endif // LLVM_LIBC_SRC_SUPPORT_FPUTIL_POLYEVAL_H