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Programming-Idioms

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Idiom #364 Calculate the order of magnitude for a value

Calculate the `SI prefix`, s, of value a.

For example, `k, M, G, T, etc.`

https://en.wikipedia.org/wiki/Metric_prefix
https://en.wikipedia.org/wiki/Orders_of_magnitude_(bit_rate)

#include <cmath>
#include <vector>
using namespace std;
struct units {
    double y;
    vector<char> a;
    units(int x) { y = log(x); }
    void add(char x) { a.push_back(x); }
    pair<int, char> get(int x) {
        int i (log(x) / y);
        return {i, a[i - 1]};
    }
};
units u {1'000};
for (char x : "kMGT") u.add(x);
pair p {u.get(a)};
a /= pow(1'000, p.first);
char x {p.second};
#include <cmath>
int y (log(a) / log(1'000));
a /= pow(1'000, y);
char x {"kMGT"[y - 1]};
import static java.lang.Math.log;
import static java.lang.Math.pow;
enum SI {
    k("kilo"),
    M("mega"),
    G("giga"),
    T("tera");
    String s;
    static double y = log(1_000);
    SI(String s) { this.s = s; }
    static SI get(double x) {
        int y = (int) (log(x) / SI.y);
        return values()[y - 1];
    }
}
SI si = SI.get(a);
a /= pow(1_000, si.ordinal() + 1);
String x = si.name();
import static java.lang.Math.log;
import static java.lang.Math.pow;
int y = (int) (log(a) / log(1_000));
a /= pow(1_000, y);
char x = "kMGT".charAt(y - 1);
function GetSIPrefix(AValue: Double): string;
const
  SIPrefixes: array[1..24] of String = ('Q','R','Y', 'Z','E','P','T','G','M','K','H','D','','d','c','m','µ','mc','n','p','f','a','z','y');
  SIFactors:  array[1..24] of Double = (1E+30,1E+27,1E+24, 1E+21, 1E+18, 1E+15, 1E+12, 1E+9, 1E+6, 1E+3,1E+2,1E+1,1,1E-1,1E-2,
var
  i: Integer;
begin
  Result := '';
  for i := 1 to 24 do
  begin
    if (Abs(AValue) >= SIFactors[i]) then
    begin
      Exit(SIPrefixes[i]);
    end;
  end;
end;
from math import log
class MetricPrefix(list):
    def append(self, *args):
        n = len(self) + 1
        arg = *args, 1_000 ** n
        super().append(arg)
    def __getitem__(self, key):
        if type(key) == int:
            i = int(log(key, 1_000)) - 1
            return super().__getitem__(i)
        for values in self:
            if key in values:
                return values
m = MetricPrefix()
m.append('k', 'kilo')
m.append('M', 'mega')
# Examples
k, kilo, value = m[1_000]
M = m['mega'][-1]
s = m[a]
from math import log
y = int(log(a, 1_000))
a /= 1_000 ** y
s = 'kMGT'[y - 1]
def metric_prefix(value):
    for n, prefix in enumerate('kMGT', 1):
        b = 1_000 ** n
        if value in range(b, b * 1_000):
            return f'{value / b} {prefix}'
s = f'{a} B is {metric_prefix(a)}B'
b = 1_000
match a:
    case v if v in range(b, b ** 2):
        s = v / 1e3, 'k', 'kilo'
    case v if v in range(b ** 2, b ** 3):
        s = v / 1e6, 'M', 'mega'
    case v if v in range(b ** 3, b ** 4):
        s = v / 1e9, 'G', 'giga'
    case v if v in range(b ** 4, b ** 5):
        s = v / 1e12, 'T', 'tera'
x =  case a
  when 1e3... 1e6 ; "k"
  when 1e6... 1e9 ; "M"
  when 1e9... 1e12; "G"
  when 1e12...1e15; "T"
  else ""
end
New implementation...
< > ⌨
reilas 
using namespace std;
struct units {
    double y;
    vector<char> a;
    units(int x) { y = log(x); }
    void add(char x) { a.push_back(x); }
    pair<int, char> get(int x) {
        int i (log(x) / y);
        return {i, a[i - 1]};
    }
};
units u {1'000};
for (char x : "kMGT") u.add(x);
pair p {u.get(a)};
a /= pow(1'000, p.first);
char x {p.second};
int y (log(a) / log(1'000));
a /= pow(1'000, y);
char x {"kMGT"[y - 1]};
enum SI {
    k("kilo"),
    M("mega"),
    G("giga"),
    T("tera");
    String s;
    static double y = log(1_000);
    SI(String s) { this.s = s; }
    static SI get(double x) {
        int y = (int) (log(x) / SI.y);
        return values()[y - 1];
    }
}
SI si = SI.get(a);
a /= pow(1_000, si.ordinal() + 1);
String x = si.name();
int y = (int) (log(a) / log(1_000));
a /= pow(1_000, y);
char x = "kMGT".charAt(y - 1);
function GetSIPrefix(AValue: Double): string;
const
  SIPrefixes: array[1..24] of String = ('Q','R','Y', 'Z','E','P','T','G','M','K','H','D','','d','c','m','µ','mc','n','p','f','a','z','y');
  SIFactors:  array[1..24] of Double = (1E+30,1E+27,1E+24, 1E+21, 1E+18, 1E+15, 1E+12, 1E+9, 1E+6, 1E+3,1E+2,1E+1,1,1E-1,1E-2,
var
  i: Integer;
begin
  Result := '';
  for i := 1 to 24 do
  begin
    if (Abs(AValue) >= SIFactors[i]) then
    begin
      Exit(SIPrefixes[i]);
    end;
  end;
end;
class MetricPrefix(list):
    def append(self, *args):
        n = len(self) + 1
        arg = *args, 1_000 ** n
        super().append(arg)
    def __getitem__(self, key):
        if type(key) == int:
            i = int(log(key, 1_000)) - 1
            return super().__getitem__(i)
        for values in self:
            if key in values:
                return values
m = MetricPrefix()
m.append('k', 'kilo')
m.append('M', 'mega')
# Examples
k, kilo, value = m[1_000]
M = m['mega'][-1]
s = m[a]
y = int(log(a, 1_000))
a /= 1_000 ** y
s = 'kMGT'[y - 1]
def metric_prefix(value):
    for n, prefix in enumerate('kMGT', 1):
        b = 1_000 ** n
        if value in range(b, b * 1_000):
            return f'{value / b} {prefix}'
s = f'{a} B is {metric_prefix(a)}B'
b = 1_000
match a:
    case v if v in range(b, b ** 2):
        s = v / 1e3, 'k', 'kilo'
    case v if v in range(b ** 2, b ** 3):
        s = v / 1e6, 'M', 'mega'
    case v if v in range(b ** 3, b ** 4):
        s = v / 1e9, 'G', 'giga'
    case v if v in range(b ** 4, b ** 5):
        s = v / 1e12, 'T', 'tera'
x =  case a
  when 1e3... 1e6 ; "k"
  when 1e6... 1e9 ; "M"
  when 1e9... 1e12; "G"
  when 1e12...1e15; "T"
  else ""
end