Round Up/down with Rule Using Math Function only?

Question

Some Math people please help, I want to convert using only Math. Function. (Pow, Floor......etc) with only single statement as possile, not using if else to check if the 5fifth digits after decimals from 1-4 or 6-9 .

• i want to convert 5 digits after decimal to 5 digits after decimal with the following rules , alway 5 and 0 at the end.

Rule 1:

double number1 = 1.2345* 
if( * from 1 to 4)
   number1 ==> 1.23455 
if ( * from 6 to 9)
  number1  ==> 1.23460 

Rule 2:

double number2 = 1.2345* 
if( * from 1 to 4)
   number2 ==> 1.23450 

if ( * from 6 to 9)
  number2  ==> 1.23455 

I Came up with answer for Rule 1, but it need to 2 statement, I wonder if it can be done with only 1 statement

number1 = Math.Floor((number1 + 0.00005) * 20000) / 20000 - 0.00005;
number1 = Math.Floor((number1 + 0.00005) * 20000) / 20000 ;

Thanks

Answer 1

For rule #1:

var y = (int)((x - 0.00001) * 20000) / 20000.0 + 0.00005;

Result:

1.23450 => 1.23450
1.23451 => 1.23455
1.23452 => 1.23455
1.23453 => 1.23455
1.23454 => 1.23455
1.23455 => 1.23455
1.23456 => 1.23460
1.23457 => 1.23460
1.23458 => 1.23460
1.23459 => 1.23460
1.23460 => 1.23460

For rule #2:

var y = (int)(x * 20000) / 20000.0;

Result:

1.23450 => 1.23450
1.23451 => 1.23450
1.23452 => 1.23450
1.23453 => 1.23450
1.23454 => 1.23450
1.23455 => 1.23455
1.23456 => 1.23455
1.23457 => 1.23455
1.23458 => 1.23455
1.23459 => 1.23455