[Bug]: The "calc" option is unsafe because it rounds the resulting value not like browser (Chrome) does

[Serator]

Describe the bug

I have the following code:

html {
  font-size: calc(16 * 100 / 1920 * 1vw);
}

Google Chrome renders this as 16px.

The cssnano option calc converts these styles to
html{font-size:.83333vw}
that Google Chrome renders as `15.9999px'.

Expected behaviour

The optimized values should be the same as the original.

Steps to reproduce

https://cssnano.co/playground/#eyJpbnB1dCI6Imh0bWwge1xuICBmb250LXNpemU6IGNhbGMoMTYgKiAxMDAgLyAxOTIwICogMXZ3KTtcbn0iLCJjb25maWciOiJjc3NuYW5vLXByZXNldC1kZWZhdWx0In0=

Version

6.0.1

Preset

default

Environment

System:
    OS: Windows 10 10.0.19045
    CPU: (8) x64 Intel(R) Core(TM) i7-6700HQ CPU @ 2.60GHz
    Memory: 2.51 GB / 15.76 GB

Package details

├─┬ cssnano@6.0.1
│ ├─┬ cssnano-preset-default@6.0.1
│ │ ├─┬ css-declaration-sorter@6.4.1
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ cssnano-utils@4.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-calc@9.0.1
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-colormin@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-convert-values@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-discard-comments@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-discard-duplicates@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-discard-empty@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-discard-overridden@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-merge-longhand@6.0.0
│ │ │ ├── postcss@8.4.31 deduped
│ │ │ └─┬ stylehacks@6.0.0
│ │ │   └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-merge-rules@6.0.1
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-minify-font-values@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-minify-gradients@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-minify-params@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-minify-selectors@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-normalize-charset@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-normalize-display-values@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-normalize-positions@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-normalize-repeat-style@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-normalize-string@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-normalize-timing-functions@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-normalize-unicode@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-normalize-url@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-normalize-whitespace@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-ordered-values@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-reduce-initial@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-reduce-transforms@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-svgo@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ ├─┬ postcss-unique-selectors@6.0.0
│ │ │ └── postcss@8.4.31 deduped
│ │ └── postcss@8.4.31 deduped
│ └── postcss@8.4.31 deduped
├─┬ htmlnano@2.0.4
│ ├── cssnano@6.0.1 deduped
│ └── postcss@8.4.31 deduped
├─┬ postcss-nesting@12.0.1
│ └── postcss@8.4.31 deduped
├─┬ postcss-preset-env@9.2.0
│ ├─┬ @csstools/postcss-cascade-layers@4.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-color-function@3.0.7
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-color-mix-function@2.0.7
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-exponential-functions@1.0.1
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-font-format-keywords@3.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-gamut-mapping@1.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-gradients-interpolation-method@4.0.7
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-hwb-function@3.0.6
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-ic-unit@3.0.2
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-initial@1.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-is-pseudo-class@4.0.3
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-logical-float-and-clear@2.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-logical-resize@2.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-logical-viewport-units@2.0.3
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-media-minmax@1.1.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-media-queries-aspect-ratio-number-values@2.0.3
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-nested-calc@3.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-normalize-display-values@3.0.1
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-oklab-function@3.0.7
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-progressive-custom-properties@3.0.2
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-relative-color-syntax@2.0.7
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-scope-pseudo-class@3.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-stepped-value-functions@3.0.2
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-text-decoration-shorthand@3.0.3
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-trigonometric-functions@3.0.2
│ │ └── postcss@8.4.31 deduped
│ ├─┬ @csstools/postcss-unset-value@3.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ autoprefixer@10.4.16
│ │ └── postcss@8.4.31 deduped
│ ├─┬ css-blank-pseudo@6.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ css-has-pseudo@6.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ css-prefers-color-scheme@9.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-attribute-case-insensitive@6.0.2
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-clamp@4.1.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-color-functional-notation@6.0.2
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-color-hex-alpha@9.0.2
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-color-rebeccapurple@9.0.1
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-custom-media@10.0.2
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-custom-properties@13.3.2
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-custom-selectors@7.1.6
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-dir-pseudo-class@8.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-double-position-gradients@5.0.2
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-focus-visible@9.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-focus-within@8.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-font-variant@5.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-gap-properties@5.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-image-set-function@6.0.1
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-lab-function@6.0.7
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-logical@7.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-opacity-percentage@2.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-overflow-shorthand@5.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-page-break@3.0.4
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-place@9.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-pseudo-class-any-link@9.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-replace-overflow-wrap@4.0.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-selector-not@7.0.1
│ │ └── postcss@8.4.31 deduped
│ └── postcss@8.4.31 deduped
├── postcss@8.4.31
├─┬ svelte-check@3.5.2
│ └─┬ svelte-preprocess@5.0.4
│   └── postcss@8.4.31 deduped
├─┬ tailwindcss@3.3.3
│ ├─┬ postcss-import@15.1.0
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-js@4.0.1
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-load-config@4.0.1
│ │ └── postcss@8.4.31 deduped
│ ├─┬ postcss-nested@6.0.1
│ │ └── postcss@8.4.31 deduped
│ └── postcss@8.4.31 deduped
└─┬ vite@4.4.11
  └── postcss@8.4.31 deduped

Additional context

No response

[ludofischer]

What precision what would be acceptable to you? I don't think it's possible to ever get the right number, we can only add more 9s at the end. I am curious about the use case, with 1/10000 of a pixel, you would need a huge screen with a low resolution to see a difference. I would suggest deactivating the postcss-calc transform as I doubt it's possible to calculate an exact.