Fix #7640: tally calculation precision error

[yihuang]

Solution:

• change (a / b) * c to a * c / b

Description

closes: #7640

---

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• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer
• Review Codecov Report in the comment section below once CI passes

[codecov]

Codecov Report

Merging #7641 into master will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #7641      +/-   ##
==========================================
- Coverage   54.34%   54.34%   -0.01%     
==========================================
  Files         610      610              
  Lines       38629    38627       -2     
==========================================
- Hits        20992    20990       -2     
  Misses      15493    15493              
  Partials     2144     2144              

[amaury1093]

I've never looked at Dec's code, I thought Dec would handle arithmetic like this correctly. Anyways, this lgtm too, but I would prefer having someone with more experience on this code have a look too.

[fedekunze]

Thanks! can you add a test case that matches your example from the issue?

[cwgoes]

We should always be using this order of operations, I wonder if we can lint for it somehow.

[sunnya97]

@amaurymartiny Dec has limited precision, hardcode defaulted to 18 decimal points

[yihuang]

Thanks! can you add a test case that matches your example from the issue?

I don't know how to setup related chain environment in unit tests, or simulation tests, not clear about how the simulation framework works either, I need to read more about that.

[fedekunze]

I don't know how to setup related chain environment in unit tests, or simulation tests, not clear about how the simulation framework works either, I need to read more about that.

@yihuang It could just be a Dec unit test on types/dec_test.go

[yihuang]

I don't know how to setup related chain environment in unit tests, or simulation tests, not clear about how the simulation framework works either, I need to read more about that.

@yihuang It could just be a Dec unit test on types/dec_test.go

just added a simple test case.

[cwgoes]

utACK

[fedekunze]

I think this PR requires a Bug Fix changelog entry

[yihuang]

I think this PR requires a Bug Fix changelog entry

thanks, done.