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