[libc-commits] [libc] [llvm] [libc][math] Refactor log10, log1p, log2 implementation to header-only in src/__support/math folder. (PR #176089)

[Muhammad Bassiouni via libc-commits]

================
@@ -0,0 +1,1068 @@
+//===-- Double-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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC___SUPPORT_MATH_LOG1P_H
+#define LLVM_LIBC_SRC___SUPPORT_MATH_LOG1P_H
+
+#include "common_constants.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/dyadic_float.h"
+#include "src/__support/FPUtil/multiply_add.h"
+#include "src/__support/common.h"
+#include "src/__support/integer_literals.h"
+#include "src/__support/macros/config.h"
+#include "src/__support/macros/optimization.h" // LIBC_UNLIKELY
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace math {
+namespace log1p_internal {
+// 128-bit precision dyadic floating point numbers.
+using Float128 = typename fputil::DyadicFloat<128>;
+
+using LIBC_NAMESPACE::operator""_u128;
+
+using namespace common_constants_internal;
+
+// R1[i] = 2^-8 * nearestint( 2^8 / (1 + i * 2^-7) )
+constexpr double R1[129] = {
+    0x1p0,     0x1.fcp-1, 0x1.f8p-1, 0x1.f4p-1, 0x1.fp-1,  0x1.ecp-1, 0x1.eap-1,
+    0x1.e6p-1, 0x1.e2p-1, 0x1.dep-1, 0x1.dap-1, 0x1.d8p-1, 0x1.d4p-1, 0x1.dp-1,
+    0x1.cep-1, 0x1.cap-1, 0x1.c8p-1, 0x1.c4p-1, 0x1.cp-1,  0x1.bep-1, 0x1.bap-1,
+    0x1.b8p-1, 0x1.b4p-1, 0x1.b2p-1, 0x1.bp-1,  0x1.acp-1, 0x1.aap-1, 0x1.a6p-1,
+    0x1.a4p-1, 0x1.a2p-1, 0x1.9ep-1, 0x1.9cp-1, 0x1.9ap-1, 0x1.98p-1, 0x1.94p-1,
+    0x1.92p-1, 0x1.9p-1,  0x1.8ep-1, 0x1.8ap-1, 0x1.88p-1, 0x1.86p-1, 0x1.84p-1,
+    0x1.82p-1, 0x1.8p-1,  0x1.7ep-1, 0x1.7ap-1, 0x1.78p-1, 0x1.76p-1, 0x1.74p-1,
+    0x1.72p-1, 0x1.7p-1,  0x1.6ep-1, 0x1.6cp-1, 0x1.6ap-1, 0x1.68p-1, 0x1.66p-1,
+    0x1.64p-1, 0x1.62p-1, 0x1.6p-1,  0x1.5ep-1, 0x1.5cp-1, 0x1.5ap-1, 0x1.58p-1,
+    0x1.58p-1, 0x1.56p-1, 0x1.54p-1, 0x1.52p-1, 0x1.5p-1,  0x1.4ep-1, 0x1.4cp-1,
+    0x1.4ap-1, 0x1.4ap-1, 0x1.48p-1, 0x1.46p-1, 0x1.44p-1, 0x1.42p-1, 0x1.42p-1,
+    0x1.4p-1,  0x1.3ep-1, 0x1.3cp-1, 0x1.3cp-1, 0x1.3ap-1, 0x1.38p-1, 0x1.36p-1,
+    0x1.36p-1, 0x1.34p-1, 0x1.32p-1, 0x1.3p-1,  0x1.3p-1,  0x1.2ep-1, 0x1.2cp-1,
+    0x1.2cp-1, 0x1.2ap-1, 0x1.28p-1, 0x1.28p-1, 0x1.26p-1, 0x1.24p-1, 0x1.24p-1,
+    0x1.22p-1, 0x1.2p-1,  0x1.2p-1,  0x1.1ep-1, 0x1.1cp-1, 0x1.1cp-1, 0x1.1ap-1,
+    0x1.1ap-1, 0x1.18p-1, 0x1.16p-1, 0x1.16p-1, 0x1.14p-1, 0x1.14p-1, 0x1.12p-1,
+    0x1.12p-1, 0x1.1p-1,  0x1.0ep-1, 0x1.0ep-1, 0x1.0cp-1, 0x1.0cp-1, 0x1.0ap-1,
+    0x1.0ap-1, 0x1.08p-1, 0x1.08p-1, 0x1.06p-1, 0x1.06p-1, 0x1.04p-1, 0x1.04p-1,
+    0x1.02p-1, 0x1.02p-1, 0x1p-1,
+};
+
+// Extra constants for exact range reduction when FMA instructions are not
+// available:
+// r * c - 1 for r = 2^-8 * nearestint( 2^8 / (1 + i * 2^-7))
+//           and c = 1 + i * 2^-7
+//           with i = 0..128.
+[[maybe_unused]] constexpr double RCM1[129] = {
----------------
bassiounix wrote:

```suggestion
[[maybe_unused]] LIBC_INLINE_VAR constexpr double RCM1[129] = {
```

https://github.com/llvm/llvm-project/pull/176089