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Re: Optimization for std::to_string()

From: Jonathan Wakely <jwakely at redhat dot com>
To: niXman <i dot nixman at autistici dot org>
Cc: gcc-patches at gcc dot gnu dot org, libstdc++ at gcc dot gnu dot org
Date: Fri, 20 Jul 2018 14:49:15 +0100
Subject: Re: Optimization for std::to_string()
References: <c9b263c6182555a3241c48f368e477e5@autistici.org> <20180720100522.GP14057@redhat.com> <bf1d55977a3cda4705a4d8e86538db23@autistici.org>

On 20/07/18 13:51 +0300, niXman wrote:

Jonathan Wakely 2018-07-20 13:05:

On 20/07/18 12:44 +0300, niXman wrote:

Thanks. How did you verify it's an optimization?

Optimization is that there is no superfluous copying into string.

The to_string functions always pass at least __n=16 to __to_xstring,
which is larger than the SSO buffer in std::__cxx11::string, and so
forces a memory allocation.

I didn't think about this...


Avoiding an unconditional dynamic allocation is the main advantage of
using alloca.

References:
- Optimization for std::to_string()
  - From: niXman
- Re: Optimization for std::to_string()
  - From: Jonathan Wakely
- Re: Optimization for std::to_string()
  - From: niXman

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