# How to tell VS Code to use the fast math option?

**URL:** https://discourse.julialang.org/t/how-to-tell-vs-code-to-use-the-fast-math-option/18257
**Category:** VS Code
**Tags:** fast-math
**Created:** [December 3, 2018, 5:49pm UTC](https://discourse.julialang.org/t/how-to-tell-vs-code-to-use-the-fast-math-option/18257 "2018-12-03T17:49:21Z")
**Posts on this page:** 1
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### Author: ![StefanKarpinski](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/stefankarpinski/32/24_2.png) [@StefanKarpinski](https://discourse.julialang.org/u/StefanKarpinski)
#### Post date: [December 3, 2018, 6:51pm UTC](https://discourse.julialang.org/t/how-to-tell-vs-code-to-use-the-fast-math-option/18257/2 "2018-12-03T18:51:15Z")

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You really don’t want to use `--math-mode=fast`. You’re telling the compiler to do something that’s fundamentally broken, e.g. [sinpi and cospi return incorrect results when using `--math-mode=fast` · Issue #30073 · JuliaLang/julia · GitHub](https://github.com/JuliaLang/julia/issues/30073). The global flag is much worse than the occasional use of the `@fastmath` macro, which is far less broken, but still may cause incorrect results. You shouldn’t use `--math-mode=fast` unless you’re willing to take the risk that all of your results might be wrong.

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