# Request for Comments: Add a Logical Shift Operator For Strings

- Version: 1.0
- Date: 2011-17-07
- Author: Anthony Ferrara ircmaxell@php.net
- Status: Inactive
- First Published at: http://wiki.php.net/rfc/logicalshiftoperator

## Introduction

This RFC is to discuss the addition of 2 new operators to the core, a logical left shift and a logical right shift.

### Why do we need new operators?

The currently implemented left and right shift operators (`<<`

and `>>`

respectively) perform arithmetic shifts. I am proposing the introduction of a pair of logical shift operators which perform their operations on arbitrary length strings.

The problem can be seen by trying to shift `-1`

(`0xFFFFFFFF`

on 32 bit, `0xFFFFFFFFFFFFFFFF`

on 64 bit). If we try `-1 >> 1`

, we get back `-1`

again. This is due to the shift being arithmetic. If we try `-1 >> 2`

, we will still get `-1`

.

Additionally, the current shifts only work on strings when the string is parsable as a number. So `“2” >> 1`

yields `1`

instead of the expected logical value of `0x19`

.

At present, if you want to do a logical shift on a string, you need to iterate over the string and apply the shift to each part of it (where the part is less than 4 bytes long, to prevent issues on 32 bit systems). For example:

For example, to implement a logical left shift currently requires something like this (this example could be optimized, but the basics of it are there):

$mask = (0xff << (8 - $bits)) & 0xff; $state = 0; $length = strlen($data); for ($i = $length - 1; $i >= 0; $i--) { $tmp = ord($data[$i]); $result .= chr(($tmp << $bits) | $state); $state = ($tmp & $mask) >> (8 - $bits); } return strrev($result);

Other bitwise operators do operate properly on strings (such as XOR - `^`

, AND - `&`

and OR - `|`

). So it would be complete to add support for shifting strings.

## Proposal

I propose the addition of two new operators which will perform a logical shift. The selection of the operators is a little bit more difficult as `<<<`

is already taken by heredoc. Perhaps something like `b<<`

...

Example:

`$foo = “a long string” {operator} 1;`

Would yield a string with the following bits:

`0xc240d8dedcce40e6e8e4d2dcce`

## Changelog

- Added note about <<< being used by heredoc already.