ios - Round number to nearest "nth" based on first non zero -

i want round double nearest non 0 number follows decimal.

for example:

x = 0.002341 rounded = 0.002  x = 0.000048123 rounded = 0.00005 

for cases base number > 0, should perform such

x = 1.000234 rounded = 1.0002 

i know can use double(round(1000*x)/1000) if know number of digits, want work number. there swift function this?

you can have little fun logarithms solve this:

func roundfirst(x:double) -> double {     if x == 0 {         return x;     }     let mul : double = pow(10, floor(log10(abs(x))))     return round(x/mul)*mul } 

the non-fractional part of log10(abs(x)) gives positive or negative power of ten of inverse of number use multiplier. floor drops fraction, , pow(10,...) gives multiplier use in rounding trick.

i tried in playground few numbers. here i've got:

println(roundfirst(0.002341))     // 0.002 println(roundfirst(0.000048123))  // 5e-05 println(roundfirst(0.0))          // 0.0 println(roundfirst(2.6))          // 3.0 println(roundfirst(123.0))        // 100 println(roundfirst(-0.002341))    // -0.002 println(roundfirst(-0.000048123)) // -5e-05 println(roundfirst(-2.6))         // -3.0 println(roundfirst(-123.0))       // -100