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Invalid plan arising from integer rounding #190

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merged 4 commits into from
May 12, 2022
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bendbennett
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@bendbennett bendbennett commented May 11, 2022

Overview

Issue 1

A lossy conversion between int64 and uint64 can arise because of the use of float64(), which has a precision of 53.

This issue arises in the following locations:

Taking the form:

return NewValue(Number, big.NewFloat(float64(rv))), nil

Issue 2

Another potential lossy operation can arise from the usage of big.Float.Set.

This issue arises in the following location:

This is a consequence of the following:

v, ok := val.value.(*big.Float)
if !ok {
	return fmt.Errorf("can't unmarshal %s into %T, expected *big.Float", val.Type(), dst)
}
target.Set(v)

Because v uses the default precision of 53 of big.Float

An additional consequence of using target.Set(v) is that the tests within value_msgpack_test.go would not detect this form of rounding.

Fixes

  • new(big.Float).SetInt64() or new(big.Float).SetUint64() is used as appropriate in value_msgpack.go.
  • big.Float.Copy instead of big.Float.Set is used within value.go.
  • Tests within value_msgpack_test.go have been updated to check for rounding.

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@detro detro left a comment

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👨‍🍳 😘

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@bflad bflad left a comment

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Looks good to me, just needs a CHANGELOG entry added, e.g. in .changelog/190.txt

```release-note:bug
tftypes: Prevented loss of number precision with integers between 54 and 64 bits
```

@bflad bflad added the bug Something isn't working label May 11, 2022
@bflad bflad added this to the v0.10.0 milestone May 11, 2022
@bendbennett bendbennett merged commit 4f3425d into main May 12, 2022
@bendbennett bendbennett deleted the bendbennett/issues-189 branch May 12, 2022 13:22
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Invalid plan arising from integer rounding
3 participants