Is there a (simple) way to get the “sign” of a number (integer) in PHP comparable to `gmp_sign`

^{Docs}:

- -1 negative
- 0 zero
- 1 positive

I remember there is some sort of compare function that can do this but I’m not able to find it at the moment.

I quickly compiled this (Demo) which does the job, but maybe there is something more nifty (like a single function call?), I would like to map the result onto an array:

```
$numbers = array(-100, 0, 100);
foreach($numbers as $number)
{
echo $number, ': ', $number ? abs($number) / $number : 0, "\n";
}
```

(this code might run into floating point precision problems probably)

Related: Request #19621 Math needs a “sign()” function

Here’s a cool one-liner that will do it for you efficiently and reliably:

```
function sign($n) {
return ($n > 0) - ($n < 0);
}
```

### Answer：

In PHP 7 you should use the combined comparison operator (`<=>`

):

```
$sign = $i <=> 0;
```

### Answer：

A variant to the above in my question I tested and which works as well and has not the floating point problem:

```
min(1, max(-1, $number))
```

*Edit:* The code above has a flaw for float numbers (question was about integer numbers) in the range greater than `-1`

and smaller than `1`

which can be fixed with the following shorty:

```
min(1, max(-1, $number == 0 ? 0 : $number * INF))
```

That one still has a flaw for the float `NAN`

making it return `-1`

always. That might not be correct. Instead one might want to return `0`

as well:

```
min(1, max(-1, (is_nan($number) or $number == 0) ? 0 : $number * INF))
```

### Answer：

You can nest ternary operators:

```
echo $number, ': ', ($number >= 0 ? ($number == 0 ? 0 : 1) : -1 )
```

This has no problem with floating point precision and avoids an floating point division.

### Answer：

What’s wrong with this form?

```
if ( $num < 0 )
{
//negative
}
else if ( $num == 0 )
{
//zero
}
else
{
//positive
}
```

or ternary:

```
$sign = $num < 0 ? -1 : ( $num > 0 ? 1 : 0 );
```

Not sure of the performance of `abs`

vs value comparison, but you could use:

```
$sign = $num ? $num / abs($num) : 0;
```

and you could turn any of them into a function:

```
function valueSign($num)
{
return $sign = $num < 0 ? -1 : ( $num > 0 ? 1 : 0 );
//or
return $sign = $num ? $num / abs($num) : 0;
}
```

I suppose you could be talking about `gmp_cmp`

, which you could call as `gmp_cmp( $num, 0 );`

### Answer：

I think that gmp_sign is not very efficient because it expects a GMP or string.

($n ? abs($n)/$n : 0) is mathematically correct, but the division costs time.

The min/max solutions seem to get unnecessary complex for floats.

($n > 0) – ($n < 0) always does 2 tests and one subtraction

($n < 0 ? -1 : ($n > 0 ? 1 : 0) does one or two tests and no arithmetic, it should be most efficient.

But I don’t believe that the difference will be relevant for most use cases.

### Answer：

I know this is late but what about simply dividing the number by the abs() of itself?

Something like:

```
function sign($n) {
return $n/(abs($n));
}
```

Put whatever error handling you want for div by zero.

### Answer：

Use `strcmp`

^{Docs}:

```
echo $number, ': ', strcmp($number, 0), "\n";
```

### Answer：

Here’s one without loop:

```
function sign($number){
echo $number, ': ', $number ? abs($number) / $number : 0, "\n";
}
$numbers = array(-100, 0, 100);
array_walk($numbers, 'sign');
```

Tags: phpphp