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

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

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