php/php-src — pull request #818 by TazeTSchnitzel (2014-09-13 02:01:22+00:00)
Title: Adds M_TAU constant for τ (2π)

This makes dealing with radians much easier:

```php
$1 = M_TAU; # full turn (360˚)
$2 = M_TAU / 2; # half-circle (180˚)
$4 = M_TAU / 4; # quarter-circle (90˚)
$8 = M_TAU / 8; # eighth-circle (45˚)
```