---
title: math.log2() function
description: >
  `math.log2()` is a function returns the binary logarithm of `x`.
menu:
  flux_v0_ref:
    name: math.log2
    parent: math
    identifier: math/log2
weight: 101
---

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`math.log2()` is a function returns the binary logarithm of `x`.



##### Function type signature

```js
(x: float) => float
```

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For more information, see [Function type signatures](/flux/v0/function-type-signatures/).
{{% /caption %}}

## Parameters

### x
({{< req >}})
the value used in the operation.




## Examples

- [Return the binary logarithm of a value](#return-the-binary-logarithm-of-a-value)
- [Use math.log2 in map](#use-mathlog2-in-map)

### Return the binary logarithm of a value

```js
import "math"

math.log2(x: 3.14)// 1.6507645591169022


```


### Use math.log2 in map

```js
import "sampledata"
import "math"

sampledata.float()
    |> map(fn: (r) => ({r with _value: math.log2(x: r._value)}))

```

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{{% expand "View example input and output" %}}

#### Input data

| _time                | *tag | _value  |
| -------------------- | ---- | ------- |
| 2021-01-01T00:00:00Z | t1   | -2.18   |
| 2021-01-01T00:00:10Z | t1   | 10.92   |
| 2021-01-01T00:00:20Z | t1   | 7.35    |
| 2021-01-01T00:00:30Z | t1   | 17.53   |
| 2021-01-01T00:00:40Z | t1   | 15.23   |
| 2021-01-01T00:00:50Z | t1   | 4.43    |

| _time                | *tag | _value  |
| -------------------- | ---- | ------- |
| 2021-01-01T00:00:00Z | t2   | 19.85   |
| 2021-01-01T00:00:10Z | t2   | 4.97    |
| 2021-01-01T00:00:20Z | t2   | -3.75   |
| 2021-01-01T00:00:30Z | t2   | 19.77   |
| 2021-01-01T00:00:40Z | t2   | 13.86   |
| 2021-01-01T00:00:50Z | t2   | 1.86    |


#### Output data

| _time                | _value             | *tag |
| -------------------- | ------------------ | ---- |
| 2021-01-01T00:00:00Z | NaN                | t1   |
| 2021-01-01T00:00:10Z | 3.4489009511451276 | t1   |
| 2021-01-01T00:00:20Z | 2.877744249949002  | t1   |
| 2021-01-01T00:00:30Z | 4.131754090984813  | t1   |
| 2021-01-01T00:00:40Z | 3.9288440367125674 | t1   |
| 2021-01-01T00:00:50Z | 2.1473066987802936 | t1   |

| _time                | _value             | *tag |
| -------------------- | ------------------ | ---- |
| 2021-01-01T00:00:00Z | 4.3110671022555955 | t2   |
| 2021-01-01T00:00:10Z | 2.3132458517875616 | t2   |
| 2021-01-01T00:00:20Z | NaN                | t2   |
| 2021-01-01T00:00:30Z | 4.305240965954483  | t2   |
| 2021-01-01T00:00:40Z | 3.792855352362489  | t2   |
| 2021-01-01T00:00:50Z | 0.8953026213333067 | t2   |

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