From: Fred Morcos <fred.morcos@open-xchange.com>
Date: Mon, 21 Mar 2022 13:52:55 +0000 (+0100)
Subject: Checked int conversions: Avoid checks when boundary values are equal
X-Git-Tag: rec-4.7.0-beta1~41^2
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=bfd1f31bddfe3d214652274aff6f9edf88eb334b;p=thirdparty%2Fpdns.git

Checked int conversions: Avoid checks when boundary values are equal
---

diff --git a/pdns/misc.hh b/pdns/misc.hh
index 4d27de7017..aee835b063 100644
--- a/pdns/misc.hh
+++ b/pdns/misc.hh
@@ -656,8 +656,20 @@ auto checked_conv(F from) -> T
   static_assert((std::numeric_limits<F>::is_signed && std::numeric_limits<T>::is_signed) || (!std::numeric_limits<F>::is_signed && !std::numeric_limits<T>::is_signed),
                 "checked_conv: The `T` and `F` types must either both be signed or unsigned");
 
-  if (from < std::numeric_limits<T>::min() || from > std::numeric_limits<T>::max()) {
-    throw std::out_of_range("checked_conv: conversion from value that is out of range for target type");
+  constexpr auto tMin = std::numeric_limits<T>::min();
+  if constexpr (std::numeric_limits<F>::min() != tMin) {
+    if (from < tMin) {
+      string s = "checked_conv: source value " + std::to_string(from) + " is smaller than target's minimum possible value " + std::to_string(tMin);
+      throw std::out_of_range(s);
+    }
+  }
+
+  constexpr auto tMax = std::numeric_limits<T>::max();
+  if constexpr (std::numeric_limits<F>::max() != tMax) {
+    if (from > tMax) {
+      string s = "checked_conv: source value " + std::to_string(from) + " is larger than target's maximum possible value " + std::to_string(tMax);
+      throw std::out_of_range(s);
+    }
   }
 
   return static_cast<T>(from);