Patch: Remove unneeded double operation in libstdc++-v3/src/c++17/fs_path.cc

[Martin Küttler]

This is a small change to libstdc++ which does not change any behavior.

This change has two, ihmo positive, implications:

 - The implicit conversion from double to int is avoided (Avoiding a
   warning).

 - No floating point number is used at all, which could be significant
   in some scenarios.


diff --git a/libstdc++-v3/src/c++17/fs_path.cc 
b/libstdc++-v3/src/c++17/fs_path.cc
index d65b5482e8b..b47ed0aa7aa 100644
--- a/libstdc++-v3/src/c++17/fs_path.cc
+++ b/libstdc++-v3/src/c++17/fs_path.cc
@@ -447,8 +447,9 @@ path::_List::reserve(int newcap, bool exact = false)

   if (curcap < newcap)
 {
-  if (!exact && newcap < int(1.5 * curcap))
-   newcap = 1.5 * curcap;
+  const int nextcap = curcap + curcap / 2;
+  if (!exact && newcap < nextcap)
+   newcap = nextcap;

   void* p = ::operator new(sizeof(_Impl) + newcap * sizeof(value_type));
   std::unique_ptr<_Impl, _Impl_deleter> newptr(::new(p) _Impl{newcap});


-- 
Kernkonzept GmbH at Dresden, Germany, HRB 31129, CEO Dr.-Ing. Michael Hohmuth

Re: Patch: Remove unneeded double operation in libstdc++-v3/src/c++17/fs_path.cc

[Martin Küttler]

>>This is a small change to libstdc++ which does not change any behavior.
>
> Please CC the libstd...@gcc.gnu.org list on all libstdc++ patches, as
> documented at https://gcc.gnu.org/lists.html

Acknowledged. Sorry.

>>This change has two, ihmo positive, implications:
>>
>> - The implicit conversion from double to int is avoided (Avoiding a
>>   warning).
>
> I don't see any warning here. What do you see?

I see "warning: conversion from ‘double’ to ‘int’ may change value
[-Wfloat-conversion]" This appears to be a specifically enabled warning.

> Looking at path::_List::reserve now, we probably also want to avoid
> overflow. Although a path with INT_MAX/1.5 components seems
> implausible for 32-bit and 64-bit targets, it could be a problem for
> 16-bit targets. I'll take care of that too.

Nice catch.

Martin

--
Kernkonzept GmbH at Dresden, Germany, HRB 31129, CEO Dr.-Ing. Michael Hohmuth