# LGF_CompareLRealByPrecision (FC / 3.0.2)

Overview

Author: Siemens Digital Industry

## Short description

This function checks floating point numbers for equality, by using an approximation formula and a fixed precision by constant 1.0E-12 (pico)

### Block Interface

| LGF_CompareLRealByPrecision (FC) |
--- | --- | ---
LReal |  |  | valueA |  | Ret_Val |  |  | Bool
LReal |  |  | valueB |  |  |  |  |
LReal |  |  | precision |  |  |  |  |

### Input parameter

Identifier | Data type | Description
--- | --- | ---
valueA | LReal | First LREAL number to be compared.
valueB | LReal | Second LREAL number to be compared.
precision | LReal | Accuracy with which the two values are compared.

### Output parameter

Identifier | Data type | Description
--- | --- | ---
Ret_Val | Bool | FALSE: not equal TRUE: approximately the same

## Functional description

The comparison of the LREAL numbers is based on an given accuracy at the parameter `precision`. The difference between the two input values must be smaller than the `precision` accuracy value multiplied by one of the two input values.

Equation:

result := FALSE OR ((#valueA = 0.0) AND (ABS(#valueB) <= #precision)) OR ((#valueB = 0.0) AND (ABS(#valueA) <= #precision)) OR (ABS(#valueA - #valueB) <= (#precision * ABS(#valueA)));

## Change log

Version & Date | Change description
--- | ---
| 1.0.0 | Simatic Systems Support
| 03.06.2019 | First released version function besad on `LGF_CompareLReal`
| 3.0.0 | Simatic Systems Support
| 23.04.2020 | Set version to V3.0.0, harmonize the version of the whole library
| 3.0.1 | Simatic Systems Support
| 19.01.2020 | Insert documentation
| 3.0.2 | Simatic Systems Support
| 21.12.2023 | Fix compare error if one value is exactly zero