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Programming-Idioms

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Idiom #367 Find the next significant digit

Floor a decimal value, x, to the first significant digit.

For example, 1.0234 is ≈ 1.02.

https://en.wikipedia.org/wiki/Significant_figures

from decimal import Decimal
from math import floor, modf, log
num, integer = modf(x)
y = log(num) / log(Decimal('.1'))
denom = 10 ** (floor(y) + 1)
x = int(x * denom) / denom
#include <cmath>
double i, n {modf(x, &i)},
       y {log(n) / log(.1)},
       d {pow(10, floor(y) + 1)};
x = trunc(x * d) / d;
let i = Math.trunc(x),
    n = x - i,
    y = Math.log(n) / Math.log(.1),
    d = Math.pow(10, Math.trunc(y) + 1)
x = Math.trunc(x * d) / d
import static java.lang.Math.log;
import static java.lang.Math.pow;
double i = (int) x,
       n = x - i,
       y = log(n) / log(.1),
       d = pow(10, (int) y + 1);
x = (int) (x * d) / d;
  str(x,s);
  p := Pos('.',s) + 1;
  while (s[p] = '0') do inc(p);
  setlength(s,p);
New implementation...
< > ⌨
reilas 
num, integer = modf(x)
y = log(num) / log(Decimal('.1'))
denom = 10 ** (floor(y) + 1)
x = int(x * denom) / denom
double i, n {modf(x, &i)},
       y {log(n) / log(.1)},
       d {pow(10, floor(y) + 1)};
x = trunc(x * d) / d;
let i = Math.trunc(x),
    n = x - i,
    y = Math.log(n) / Math.log(.1),
    d = Math.pow(10, Math.trunc(y) + 1)
x = Math.trunc(x * d) / d
double i = (int) x,
       n = x - i,
       y = log(n) / log(.1),
       d = pow(10, (int) y + 1);
x = (int) (x * d) / d;
  str(x,s);
  p := Pos('.',s) + 1;
  while (s[p] = '0') do inc(p);
  setlength(s,p);