Re: math operations with base#prefix

[alex xmb ratchev]

On Mon, Sep 18, 2023, 04:03 Kerin Millar <kfm@plushkava.net> wrote:

> Hi Victor,
>
> On Sun, 17 Sep 2023, at 8:59 PM, Victor Pasko wrote:
> > Hi,
> >
> > Could you please take a look at attached bug.bash.
> >
> > Maybe, not all math combinations were presented there or the test has
> > duplications somehow.
> > Here are results of several runs with test# as argument
> >
> >
> > *% bash --version*GNU bash, version 5.2.15(3)-release (x86_64-pc-cygwin)
> >
> > Good test without argument but others with errors :(
> > *% ./bug.bash*
> >
> > res1=010 good 010 base8
> > res2=03 good 03 base8
> > res=17 good result 17 base10 (res1+3*res2)
> > base10-res=19 good result 19 base10 (res1+3*res2)
> > base10-res=19 good result 19 base10 (res1+3*res2)
> > base10-res=19 good result 19 base10 (res1+3*res2)
> > res1=8 good result 8 base10
> > res1=10 good result 10
> > res1=10 good result 10
> > res1=010 good result 010 base8
> > base10-res1=10 good result 10
> > res1=16 good result 16
> >
> >
> > *% ./bug.bash 1*
> > TESTCASE=1
> > res1=010 good 010 base8
> > res2=03 good 03 base8
> > res=17 good result 17 base10 (res1+3*res2)
> > base10-res=19 good result 19 base10 (res1+3*res2)
> > ./bug.bash: line 29: let: res = base10#010 + base10#03 * 3: syntax error:
> > invalid arithmetic operator (error token is "#010 + base10#03 * 3")
>
> This seems like a misinterpretation of the manual. The manual states that
> numbers "take the form [base#]n, where the optional base is a decimal
> number between 2 and 64 representing the arithmetic base". As such,
> "base10" is not a decimal number between 2 and 64, whereas "10" would be.
>
> > base10-res=19 good result 19 base10 (res1+3*res2)
> > base10-res=19 good result 19 base10 (res1+3*res2)
> > res1=8 good result 8 base10
> > res1=10 good result 10
> > res1=10 good result 10
> > res1=010 good result 010 base8
> > base10-res1=10 good result 10
> > res1=16 good result 16
> >
> >
> > *% ./bug.bash 2*
> > TESTCASE=2
> > res1=010 good 010 base8
> > res2=03 good 03 base8
> > res=17 good result 17 base10 (res1+3*res2)
> > base10-res=19 good result 19 base10 (res1+3*res2)
> > base10-res=19 good result 19 base10 (res1+3*res2)
> > ./bug.bash: line 35: let: res = 10#res1: value too great for base (error
> > token is "10#res1")
>
> For numbers in the form "[base#]n", it isn't practically possible for n to
> be specified using a variable without prefixing it with a sigil (so that it
> is treated as a parameter expansion and injected). There is a very good
> reason for this: numbers in a base higher than 10 can require alphabetical
> letters to be expressed. Consider the following example.
>
> $ echo $(( 16#ff ))
> 255
>

some were prefixed with 0 which make those also not work

This is the appropriate outcome. It would be undesirable for "ff" to be
> treated as a variable name identifier there.
>
> In your case, the error is that the letters "r", "e" and "s" have ordinal
> values that are too high to be valid for base 10, but they could have been
> valid for a higher base.
>
> $ echo $(( 29#res1 ))
> 671090
>
> --
> Kerin Millar <kfm@plushkava.net>
>
>