[libc-commits] [libc] [llvm] [libc][math] Refactor pow to Header Only. (PR #176529)

[Nico Weber via libc-commits]

================
@@ -0,0 +1,544 @@
+//===-- Implementation header for pow ------------------------*- 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_POW_H
+#define LLVM_LIBC_SRC___SUPPORT_MATH_POW_H
+
+#include "hdr/errno_macros.h"
+#include "hdr/fenv_macros.h"
+#include "src/__support/CPP/bit.h"
+#include "src/__support/FPUtil/FEnvImpl.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/FPUtil/PolyEval.h"
+#include "src/__support/FPUtil/double_double.h"
+#include "src/__support/FPUtil/multiply_add.h"
+#include "src/__support/FPUtil/nearest_integer.h"
+#include "src/__support/FPUtil/sqrt.h" // Speedup for pow(x, 1/2) = sqrt(x)
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/optimization.h" // LIBC_UNLIKELY
+#include "src/__support/math/common_constants.h" // Lookup tables EXP_M1 and EXP_M2.
+#include "src/__support/math/exp_constants.h" // Lookup tables EXP_M1 and EXP_M2.
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace math {
+
+using fputil::DoubleDouble;
+
+namespace {
+
+using namespace common_constants_internal;
+
+// Constants for log2(x) range reduction, generated by Sollya with:
+// > for i from 0 to 127 do {
+//     r = 2^-8 * ceil( 2^8 * (1 - 2^(-8)) / (1 + i*2^-7) );
+//     b = nearestint(log2(r) * 2^41) * 2^-41;
+//     c = round(log2(r) - b, D, RN);
+//     print("{", -c, ",", -b, "},");
+//   };
+// This is the same as -log2(RD[i]), with the least significant bits of the
+// high part set to be 2^-41, so that the sum of high parts + e_x is exact in
+// double precision.
+// We also replace the first and the last ones to be 0.
+constexpr DoubleDouble LOG2_R_DD[128] = {
----------------
nico wrote:

Add `LIBC_INLINE_VAR` in front of all constexpr variables.

https://github.com/llvm/llvm-project/pull/176529