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 
14 // Evaluate polynomial using Horner's Scheme:
15 // With polyeval(x, a_0, a_1, ..., a_n) = a_n * x^n + ... + a_1 * x + a_0, we
16 // evaluated it as:  a_0 + x * (a_1 + x * ( ... (a_(n-1) + x * a_n) ... ) ) ).
17 // We will use FMA instructions if available.
18 // Example: to evaluate x^3 + 2*x^2 + 3*x + 4, call
19 //   polyeval( x, 4.0, 3.0, 2.0, 1.0 )
20 
21 namespace __llvm_libc {
22 namespace fputil {
23 
24 template <typename T> static inline T polyeval(T x, T a0) { return a0; }
25 
26 template <typename T, typename... Ts>
27 static inline T polyeval(T x, T a0, Ts... a) {
28   return multiply_add(x, polyeval(x, a...), a0);
29 }
30 
31 } // namespace fputil
32 } // namespace __llvm_libc
33 
34 #endif // LLVM_LIBC_SRC_SUPPORT_FPUTIL_POLYEVAL_H
35