[libc-commits] [libc] [libc][math] Add shared functions to check exceptions for exp* functions. (PR #202503)

[Hubert Tong via libc-commits]

================
@@ -0,0 +1,84 @@
+//===-- Check exceptions for exp functions ----------------------*- 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_CHECK_EXP_EXCEPTIONS_H
+#define LLVM_LIBC_SRC___SUPPORT_MATH_CHECK_EXP_EXCEPTIONS_H
+
+#include "hdr/fenv_macros.h"
+#include "src/__support/FPUtil/FPBits.h"
+#include "src/__support/common.h"
+#include "src/__support/macros/config.h"
+
+namespace LIBC_NAMESPACE_DECL {
+
+namespace math {
+
+namespace check {
+
+namespace exp_internal {
+
+template <typename T> struct Bounds;
+
+template <> struct Bounds<float> {
+  // Smallest value that will cause overflow, generated from Sollya:
+  // > float_max = 2^127 * (2 - 2^-23);
+  // > upper = round(log(float_max), SG, RU);
+  // > printfloat(upper);
+  static constexpr float UPPER = 0x1.62e43p6f;
+  static constexpr uint32_t UPPER_BITS = 0x42b1'7218;
+  // Largest value that will cause underflow, generated from Sollya:
+  // > float_min = 2^-126;
+  // > lower = round(log(float_min), SG, RD);
+  // > printfloat(lower);
+  static constexpr float LOWER = -0x1.5d58ap6f;
+  static constexpr uint32_t LOWER_BITS = 0xc2ae'ac50;
+};
+
+template <> struct Bounds<double> {
+  // Smallest value that will cause overflow, generated from Sollya:
+  // > double_max = 2^1023 * (2 - 2^-52);
+  // > upper = round(log(double_max), D, RU);
+  // > printdouble(upper);
+  static constexpr double UPPER = 0x1.62e42fefa39fp9;
+  static constexpr uint64_t UPPER_BITS = 0x4086'2e42'fefa'39f0;
+  // Largest value that will cause underflow, generated from Sollya:
+  // > double_min = 2^-1022;
----------------
hubert-reinterpretcast wrote:

Similarly, `2^-1022 - 2^(-1022 - 53)`.

https://github.com/llvm/llvm-project/pull/202503