====== Request for Comments: Add grisu3 strtod algorithm to PHP ======
  * Version: 0.9
  * Date: 2011-07-15
  * Author: David Soria Parra <dsp at php dot net>
  * Status: Inactive
  * Proposed for: PHP 5.4

===== Introduction =====

Converting strings to doubles is a common problem in applications. The current standard in solving this problem
is David Gays strtod algorithm. This algorithm is used in PHP and can be found in zend_strtod. Recently
Florian Loitsch found a new algorithm, called grisu3, to this problem. His algorithm is faster than David Gays algorithm. An
OpenSource implementation exists [[http://code.google.com/p/double-conversion/|here]]. The grisu3 algorithm fails in about
0.5% cases. The library will fall back to David Gays algorithm in that case.

===== Proposal =====

  * add grisu3 library to PHP source
  * add grisu3 to the PHP build system
  * add --enable-grisu3 option to PHP configure. disabled by default.

===== Why do we need a new strtod? =====

Using grisu3 will speed up string to double and double to string conversions. In particular json_encode and json_decode
of json data includign doubles will be faster. Simple microbenchmarks show about 20% faster json_decode.

The library includes strtod (string to double) and dtoa (double to string) conversion methods.
zend_strtod and zend_dtoa will provide the same signature. The current algorithm will be moved to zend_strtod_dragon4.c
and the zend_strtod/dtoa wrapper for the double-conversion library will go to zend_strtdo_grisu3.cc

===== Common Misconceptions =====

The grisu3 algorithm is optional. By default we still use David Gays algorithm. There is no BC break in the
API.

===== Caveats  =====

The double-conversion library is written in C++. To compile PHP with grisu3 you will need a C++ compiler.

===== Proposal and Patch =====

There is a initial patchset at http://bitbucket.org/segv/php-src

===== More about Grisu3 =====

http://www.serpentine.com/blog/2011/06/29/here-be-dragons-advances-in-problems-you-didnt-even-know-you-had/

===== Changelog =====