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

[Hubert Tong via libc-commits]

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@@ -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);
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hubert-reinterpretcast wrote:

> if we consider the `FE_UPWARD`, the overflow will in theory happens earlier than `FE_TONEAREST`

True, but I think documenting the calculation with both values and the conclusion that one boundary value works for all rounding modes is what should happen.

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