---
title: Float literal approximates a known mathematical constant
description: Datadog, the leading service for cloud-scale monitoring.
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  Docs > Datadog Security > Code Security > Static Code Analysis (SAST) > SAST
  Rules > Float literal approximates a known mathematical constant
---

# Float literal approximates a known mathematical constant

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## Metadata{% #metadata %}

**ID:** `rust-code-quality/approx-constant`

**Language:** Rust

**Severity:** Error

**Category:** Error Prone

**CWE**: [682](https://cwe.mitre.org/data/definitions/682.html)

## Description{% #description %}

Using a hand-written approximation of a floating-point constant defined in `std::f32::consts` or `std::f64::consts`. The standard library constants carry the maximum precision available for the type so they should be used. For example `std::f64::consts::PI`

## Non-Compliant Code Examples{% #non-compliant-code-examples %}

```rust
// approximate PI
let a = 3.14;
// approximate E
let b = 2.7183_f64;
```

## Compliant Code Examples{% #compliant-code-examples %}

```rust
let a = std::f32::consts::PI;
let b = std::f64::consts::E;
let c = 3.1;
```
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