llvm/libc/src/math/generic/log1pf.cpp

//===-- Single-precision log1p(x) function --------------------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//

#include "src/math/log1pf.h"
#include "common_constants.h" // Lookup table for (1/f) and log(f)
#include "src/__support/FPUtil/FEnvImpl.h"
#include "src/__support/FPUtil/FMA.h"
#include "src/__support/FPUtil/FPBits.h"
#include "src/__support/FPUtil/PolyEval.h"
#include "src/__support/FPUtil/except_value_utils.h"
#include "src/__support/FPUtil/multiply_add.h"
#include "src/__support/common.h"
#include "src/__support/macros/config.h"
#include "src/__support/macros/optimization.h" // LIBC_UNLIKELY
#include "src/__support/macros/properties/cpu_features.h"

// This is an algorithm for log10(x) in single precision which is
// correctly rounded for all rounding modes.
// - An exhaustive test show that when x >= 2^45, log1pf(x) == logf(x)
// for all rounding modes.
// - When 2^(-6) <= |x| < 2^45, the sum (double(x) + 1.0) is exact,
// so we can adapt the correctly rounded algorithm of logf to compute
// log(double(x) + 1.0) correctly.  For more information about the logf
// algorithm, see `libc/src/math/generic/logf.cpp`.
// - When |x| < 2^(-6), we use a degree-8 polynomial in double precision
// generated with Sollya using the following command:
//   fpminimax(log(1 + x)/x, 7, [|D...|], [-2^-6; 2^-6]);

namespace LIBC_NAMESPACE_DECL {

namespace internal {

// We don't need to treat denormal and 0
LIBC_INLINE float log(double x) { … }

} // namespace internal

LLVM_LIBC_FUNCTION(float, log1pf, (float x)) { … }

} // namespace LIBC_NAMESPACE_DECL