[ruby-core:100298] [Ruby master Bug#17214] BigDecimal exponentiation gives incorrect results

[nobu@ruby-lang.org]

Issue #17214 has been updated by nobu (Nobuyoshi Nakada).

Status changed from Open to Rejected

`BigDecimal` instances hold the precision, and it is not enough in that case.
You need to override the default precision in some operations.
```ruby
BigDecimal(2222).power(3.5, Float::DIG).to_i #=> 517135308457
```


----------------------------------------
Bug #17214: BigDecimal exponentiation gives incorrect results
https://bugs.ruby-lang.org/issues/17214#change-87883

* Author: karatedog (Földes László)
* Status: Rejected
* Priority: Normal
* ruby -v: ruby 2.7.1p83 (2020-03-31 revision a0c7c23c9c) [x86_64-linux]
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
This is an incorrect value:

```ruby
(BigDecimal("2222") ** BigDecimal("3.5")).to_i
# => 517135311000
```

This is the correct value (within Float precision):

```ruby
2222 ** 3.5
# => 517135308457.25256
```

As the Base gets larger, the problem is more visible. Wrong value, number of trailing zeroes increase:

```ruby
(BigDecimal("22222") ** BigDecimal("3.5")).to_i
# => 1635840670000000
```

Nearing maximum Float precision:

```ruby
22222 ** 3.5
# => 1635840670214066.5
```



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