[Rd] Floating point issue

[Antoine Fabri]

Thanks, I get the exact same results as yours

``` r
bitC <- function(x) noquote(vapply(as.double(x), function(x) { # split one
double
  b <- substr(as.character(rev(numToBits(x))), 2L, 2L)
      paste0(c(b[1L], " ", b[2:12], " | ", b[13:64]), collapse = "")
    }, ""))
bitC(10^25)
#> [1] 0 10001010010 | 0000100010110010101000101100001010000000001010010001
bitC(10000000000000000905969664)
#> [1] 0 10001010010 | 0000100010110010101000101100001010000000001010010010
bitC(10000000000000000905969664 - 10^25)
#> [1] 0 10000011110 | 0000000000000000000000000000000000000000000000000000
bitC(1e25)
#> [1] 0 10001010010 | 0000100010110010101000101100001010000000001010010001
```

<sup>Created on 2022-07-10 by the [reprex package](
https://reprex.tidyverse.org) (v2.0.1)</sup>

Le dim. 10 juil. 2022 à 22:23, Bill Dunlap <williamwdunlap using gmail.com> a
écrit :

> The following function, 'bitC' from ?numToBits, displays the bits in a
> double precision number, separated into the sign bit, the 11 exponent bits,
> and the 52 bits in the mantissa.  I've shown the results with your numbers
> from R-2.4.0 on my Windows 11 Lenovo laptop: what do you get?
>
> > bitC <- function(x) noquote(vapply(as.double(x), function(x) { # split
> one double
> +     b <- substr(as.character(rev(numToBits(x))), 2L, 2L)
> +     paste0(c(b[1L], " ", b[2:12], " | ", b[13:64]), collapse = "")
> +   }, ""))
> > bitC(10^25)
> # [1] 0 10001010010 | 0000100010110010101000101100001010000000001010010001
> > bitC(10000000000000000905969664)
> # [1] 0 10001010010 | 0000100010110010101000101100001010000000001010010001
> > bitC(10000000000000000905969664 - 10^25)
> # [1] 0 00000000000 | 0000000000000000000000000000000000000000000000000000
> > bitC(1e25)
> # [1] 0 10001010010 | 0000100010110010101000101100001010000000001010010001
>
> -Bill
>
> On Sun, Jul 10, 2022 at 7:00 AM Antoine Fabri <antoine.fabri using gmail.com>
> wrote:
>
>> Dear r-devel,
>>
>> For some numbers, the printed value is not equivalent to the input :
>>
>> options(scipen = 999)
>> ## GOOD
>> 1e24
>> #> [1]  999999999999999983222784
>> 1e24 == 999999999999999983222784
>> #> [1] TRUE
>>
>> ## BAD
>> 1e25
>> #> [1] 10000000000000000905969664
>> 1e25 == 10000000000000000905969664
>> #> [1] FALSE
>>
>> ## STILL BAD
>> 10000000000000000905969664
>> #> [1] 10000000000000003053453312
>>
>> ## GOOD AGAIN
>> 10000000000000003053453312
>> #> [1] 10000000000000003053453312
>>
>> # Additionally
>> 10000000000000000000000000 == 1e25
>> #> [1] FALSE
>>
>> Are these bugs ?
>>
>>         [[alternative HTML version deleted]]
>>
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>> R-devel using r-project.org mailing list
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>>
>

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