{"id":13024,"date":"2022-11-30T17:22:53","date_gmt":"2022-11-30T15:22:53","guid":{"rendered":"https:\/\/www.btc-embedded.com\/?p=13024"},"modified":"2022-12-15T13:48:21","modified_gmt":"2022-12-15T11:48:21","slug":"why-back-to-back-testing-is-still-needed-for-floating-point","status":"publish","type":"post","link":"https:\/\/www.btc-embedded.com\/de\/why-back-to-back-testing-is-still-needed-for-floating-point\/","title":{"rendered":"Why Back-to-back testing is still needed for floating-point"},"content":{"rendered":"\t\t
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Introduction<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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When I started working at BTC Embedded Systems in 2014, floating-point was a rare topic in customer meetings and many control units supported fixed-point only. But since then, floating-point became more and more important and has fully arrived in the projects today.<\/span>\u00a0<\/span><\/p>

Back-to-back testing can be used for various use cases but the most common one is to compare a Simulink model vs. auto-generated production code. In the past, this made a lot of sense since the model was usually using floating-point and the code was implemented with fixed-point. The Back-to-back test verified, if the translation from model to code does still lead to the same behavior.<\/span>\u00a0<\/span><\/p>

This raises the question, if a floating-point Back-to-back test is still needed, since both model and code use floating-point data types now.<\/span>\u00a0<\/span><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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How does floating-point work? <\/h3>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Fixed-point is not a real datatype, it could be described as a ways to implement integer datatypes with a user-defined precision. Please, also read the article What you should know about fixed-point from my colleague Markus Gros for more information.<\/span>\u00a0<\/span><\/p>

However, this is different for floating-point variables. The available bits are split into 3 different sections to represent the sign, the exponent, and the mantissa (see below).<\/span>\u00a0<\/span><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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For the value 1 with a 32-bit floating-point variable (single precision), it looks like this:<\/span>\u00a0<\/span><\/p>