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package humanize
import (
"errors"
"math"
"regexp"
"strconv"
)
var siPrefixTable = map[float64]string{
-30: "q", // quecto
-27: "r", // ronto
-24: "y", // yocto
-21: "z", // zepto
-18: "a", // atto
-15: "f", // femto
-12: "p", // pico
-9: "n", // nano
-6: "µ", // micro
-3: "m", // milli
0: "",
3: "k", // kilo
6: "M", // mega
9: "G", // giga
12: "T", // tera
15: "P", // peta
18: "E", // exa
21: "Z", // zetta
24: "Y", // yotta
27: "R", // ronna
30: "Q", // quetta
}
var revSIPrefixTable = revfmap(siPrefixTable)
// revfmap reverses the map and precomputes the power multiplier
func revfmap(in map[float64]string) map[string]float64 {
rv := map[string]float64{}
for k, v := range in {
rv[v] = math.Pow(10, k)
}
return rv
}
var riParseRegex *regexp.Regexp
func init() {
ri := `^([\-0-9.]+)\s?([`
for _, v := range siPrefixTable {
ri += v
}
ri += `]?)(.*)`
riParseRegex = regexp.MustCompile(ri)
}
// ComputeSI finds the most appropriate SI prefix for the given number
// and returns the prefix along with the value adjusted to be within
// that prefix.
//
// See also: SI, ParseSI.
//
// e.g. ComputeSI(2.2345e-12) -> (2.2345, "p")
func ComputeSI(input float64) (float64, string) {
if input == 0 {
return 0, ""
}
mag := math.Abs(input)
exponent := math.Floor(logn(mag, 10))
exponent = math.Floor(exponent/3) * 3
value := mag / math.Pow(10, exponent)
// Handle special case where value is exactly 1000.0
// Should return 1 M instead of 1000 k
if value == 1000.0 {
exponent += 3
value = mag / math.Pow(10, exponent)
}
value = math.Copysign(value, input)
prefix := siPrefixTable[exponent]
return value, prefix
}
// SI returns a string with default formatting.
//
// SI uses Ftoa to format float value, removing trailing zeros.
//
// See also: ComputeSI, ParseSI.
//
// e.g. SI(1000000, "B") -> 1 MB
// e.g. SI(2.2345e-12, "F") -> 2.2345 pF
func SI(input float64, unit string) string {
value, prefix := ComputeSI(input)
return Ftoa(value) + " " + prefix + unit
}
// SIWithDigits works like SI but limits the resulting string to the
// given number of decimal places.
//
// e.g. SIWithDigits(1000000, 0, "B") -> 1 MB
// e.g. SIWithDigits(2.2345e-12, 2, "F") -> 2.23 pF
func SIWithDigits(input float64, decimals int, unit string) string {
value, prefix := ComputeSI(input)
return FtoaWithDigits(value, decimals) + " " + prefix + unit
}
var errInvalid = errors.New("invalid input")
// ParseSI parses an SI string back into the number and unit.
//
// See also: SI, ComputeSI.
//
// e.g. ParseSI("2.2345 pF") -> (2.2345e-12, "F", nil)
func ParseSI(input string) (float64, string, error) {
found := riParseRegex.FindStringSubmatch(input)
if len(found) != 4 {
return 0, "", errInvalid
}
mag := revSIPrefixTable[found[2]]
unit := found[3]
base, err := strconv.ParseFloat(found[1], 64)
return base * mag, unit, err
}
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