property NSString : a reference to current application’s NSString
property NSNumber : a reference to current application’s NSNumber
property NSNumberFormatter : a reference to current application’s NSNumberFormatter
property NSNumberFormatterRoundUp : a reference to current application’s NSNumberFormatterRoundUp
property NSNumberFormatterRoundDown : a reference to current application’s NSNumberFormatterRoundDown

set a to "0.9096617698669434"
set a1Res to roundingDownNumStr(a, 2) of me

set b to "0.0001830748806241899"
set b1Res to roundingDownNumStr(b, 2) of me

return {a1Res, b1Res}
–>　　{​​​​​0.9, ​​​​​0.0​​​}

on roundingDownNumStr(aNum as string, aDigit as integer)
　　set a to NSString’s stringWithString:aNum
　　set aa to a’s doubleValue()
　　set aFormatter to NSNumberFormatter’s alloc()’s init()
　　aFormatter’s setMaximumFractionDigits:aDigit
　　aFormatter’s setRoundingMode:(NSNumberFormatterRoundDown)
　　set aStr to aFormatter’s stringFromNumber:aa
　　return (aStr as text) as real
end roundingDownNumStr

on roundingUpNumStr(aNum as string, aDigit as integer)
　　set a to NSString’s stringWithString:aNum
　　set aa to a’s doubleValue()
　　set aFormatter to NSNumberFormatter’s alloc()’s init()
　　aFormatter’s setMaximumFractionDigits:aDigit
　　aFormatter’s setRoundingMode:(NSNumberFormatterRoundUp)
　　set aStr to aFormatter’s stringFromNumber:aa
　　return (aStr as text) as real
end roundingUpNumStr

set theNumber to 1.234567890123E+12
set theResult to formatNumber_(theNumber)
–> "1,234,567,890,123"

set aRes to textFromNumber_forLocale_(1.2345678E+4, "fr")
–> "douze-mille-trois-cent-quarante-cinq virgule six sept huit"

set aRes to textFromNumber_forLocale_(1.2345678E+4, "ja")
–> "一万二千三百四十五・六七八"

set aRes to formatNumber_usingFormat_(1.2345678E+4, "#,###.00;0.00;(#,##0.00)")
–> "12,345.68"

on formatNumber:theNumber
　　set theFormatter to current application’s NSNumberFormatter’s new()
　　theFormatter’s setNumberStyle:(current application’s NSNumberFormatterDecimalStyle)
　　set theResult to theFormatter’s stringFromNumber:theNumber
　　return theResult as text
end formatNumber:

on textFromNumber:theNumber forLocale:localeString
　　set theFormatter to current application’s NSNumberFormatter’s new()
　　theFormatter’s setNumberStyle:(current application’s NSNumberFormatterSpellOutStyle)
　　set theLocale to current application’s NSLocale’s localeWithLocaleIdentifier:localeString
　　theFormatter’s setLocale:theLocale
　　set theResult to theFormatter’s stringFromNumber:theNumber
　　return theResult as text
end textFromNumber:forLocale:

on formatNumber:theNumber usingFormat:formatString
　　set theFormatter to current application’s NSNumberFormatter’s new()
　　theFormatter’s setFormat:formatString
　　theFormatter’s setLocalizesFormat:false
　　set theResult to theFormatter’s stringFromNumber:theNumber
　　return theResult as text
end formatNumber:usingFormat:

set c to addLargeNumber(a, b) of me

on addLargeNumber(aNum, bNum)
　　set aNumStr to aNum as string
　　set bNumStr to bNum as string
　　
　　set aCMD to "echo ＼" scale=10; " & aNumStr & "+" & bNumStr & " ＼" | bc"
　　set aRes to do shell script aCMD
　　return aRes
end addLargeNumber