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Message-ID:  <5367453E.3030906@morningstar2.co.uk>
Date:         Mon, 5 May 2014 09:01:02 +0100
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From: Joseph Wright <joseph.wright@MORNINGSTAR2.CO.UK>
Subject: Re: \__dim_strip_bp:n
To: LATEX-L@LISTSERV.UNI-HEIDELBERG.DE
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Status: R

On 05/05/2014 00:08, Heiko Oberdiek wrote:
> Hello,
>=20
> macro \__dim_strip_bp:n is defined in l3skip.dtx the following way:
>=20
>   \cs_new:Npn \__dim_strip_bp:n #1
>     { \__dim_strip_pt:n { 0.996 26 \__dim_eval:w #1 \__dim_eval_end: } =
}
>=20
> The calculation from bp to bp is essentially:
>=20
>     \dimexpr 0.99626\dimexpr #1\relax\relax
>=20
> Of course, there will always be rounding errors, but the code
> can be improved by a scaling operation inside e-TeX's \dimexpr,
> from "The e-TeX manual":
>=20
> | The arithmetic operations are performed individually, except
> | for =91scaling=92 operations (a multiplication immediately followed
> | by a division) which are performed as one combined operation
> | with a 64-bit product as intermediate value.
>=20
> Improved version with higher precision:
>=20
>   \cs_new:Npn \__dim_strip_bp:n #1
>     {
>       \__dim_strip_pt:n
>         {
>           \__dim_eval:w ( #1 ) * 800 / 803 \__dim_eval_end:
>         }
>     }
>=20
> * 800/803 is the integer fraction for 72/72.27
> * The parentheses around #1 ensure, that #1 is
>   calculated first.
>=20
> Yours sincerely
>   Heiko Oberdiek
>=20

Altered in the trunk: will feature in the next release.
--
Joseph Wright

--=20
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