return tens_cont + ones_end -- e.g. ninety-nine -> 99
end
end
end
return -1 -- Failed
end  
-- Converts a number expressed as a string in scientific notation to a string in standard decimal notation
-- e.g. 1.23E5 -> 123000, 1.23E-5 = .0000123. Conversion is exact, no rounding is performed.
local function scientific_notation_to_decimal(num)
local exponent, subs = num:gsub("^%-?%d*%.?%d*%-?[Ee]([+%-]?%d+)$", "%1")
if subs == 0 then return num end -- Input not in scientific notation, just return unmodified
exponent = tonumber(exponent)  
local negative = num:find("^%-")
local _, decimal_pos = num:find("%.")
-- Mantissa will consist of all decimal digits with no decimal point
local mantissa = num:gsub("^%-?(%d*)%.?(%d*)%-?[Ee][+%-]?%d+$", "%1%2")
if negative and decimal_pos then decimal_pos = decimal_pos - 1 end
if not decimal_pos then decimal_pos = #mantissa + 1 end  
-- Remove leading zeros unless decimal point is in first position
while decimal_pos > 1 and mantissa:sub(1,1) == '0' do
mantissa = mantissa:sub(2)
decimal_pos = decimal_pos - 1
end
-- Shift decimal point for exponent > 0
while exponent > 0 do
decimal_pos = decimal_pos + 1
exponent = exponent - 1
if decimal_pos > #mantissa + 1 then mantissa = mantissa .. '0' end
-- Remove leading zeros unless decimal point is in first position
while decimal_pos > 1 and mantissa:sub(1,1) == '0' do
mantissa = mantissa:sub(2)
decimal_pos = decimal_pos - 1
end
end
-- Shift decimal point for exponent < 0
while exponent < 0 do
if decimal_pos == 1 then
mantissa = '0' .. mantissa
else
decimal_pos = decimal_pos - 1
end
exponent = exponent + 1
end  
-- Insert decimal point in correct position and return
return (negative and '-' or '') .. mantissa:sub(1, decimal_pos - 1) .. '.' .. mantissa:sub(decimal_pos)
end  
-- Rounds a number to the nearest integer (NOT USED)
local function round_num(x)
if x%1 >= 0.5 then
return math.ceil(x)
else
return math.floor(x)
end
end  
-- Rounds a number to the nearest two-word number (round = up, down, or "on" for round to nearest).
-- Numbers with two digits before the decimal will be rounded to an integer as specified by round.
-- Larger numbers will be rounded to a number with only one nonzero digit in front and all other digits zero.
-- Negative sign is preserved and does not count towards word limit.
local function round_for_english(num, round)
-- If an integer with at most two digits, just return
if num:find("^%-?%d?%d%.?$") then return num end  
local negative = num:find("^%-")
if negative then
-- We're rounding magnitude so flip it
if round == 'up' then round = 'down' elseif round == 'down' then round = 'up' end
end  
-- If at most two digits before decimal, round to integer and return
local _, _, small_int, trailing_digits, round_digit = num:find("^%-?(%d?%d?)%.((%d)%d*)$")
if small_int then
if small_int == '' then small_int = '0' end
if (round == 'up' and trailing_digits:find('[1-9]')) or (round == 'on' and tonumber(round_digit) >= 5) then
small_int = tostring(tonumber(small_int) + 1)
end
return (negative and '-' or '') .. small_int
end  
-- When rounding up, any number with > 1 nonzero digit will round up (e.g. 1000000.001 rounds up to 2000000)
local nonzero_digits = 0
for digit in num:gfind("[1-9]") do
nonzero_digits = nonzero_digits + 1
end  
num = num:gsub("%.%d*$", "") -- Remove decimal part
-- Second digit used to determine which way to round lead digit
local _, _, lead_digit, round_digit, round_digit_2, rest = num:find("^%-?(%d)(%d)(%d)(%d*)$")
if tonumber(lead_digit .. round_digit) < 20 and (1 + #rest) % 3 == 0 then
-- In English numbers < 20 are one word so put 2 digits in lead and round based on 3rd
lead_digit = lead_digit .. round_digit
round_digit = round_digit_2
else
rest = round_digit_2 .. rest
end  
if (round == 'up' and nonzero_digits > 1) or (round == 'on' and tonumber(round_digit) >= 5) then
lead_digit = tostring(tonumber(lead_digit) + 1)
end
-- All digits but lead digit will turn to zero
rest = rest:gsub("%d", "0")
return (negative and '-' or '') .. lead_digit .. '0' .. rest
end  
local denominators = {
[2] = { 'half', plural = 'halves' },
[3] = { 'third' },
[4] = { 'quarter', us = 'fourth' },
[5] = { 'fifth' },
[6] = { 'sixth' },
[8] = { 'eighth' },
[9] = { 'ninth' },
[10] = { 'tenth' },
[16] = { 'sixteenth' },
}  
-- Return status, fraction where:
-- status is a string:
-- "finished" if there is a fraction with no whole number;
-- "ok" if fraction is empty or valid;
-- "unsupported" if bad fraction;
-- fraction is a string giving (numerator / denominator) as English text, or is "".
-- Only unsigned fractions with a very limited range of values are supported,
-- except that if whole is empty, the numerator can use "-" to indicate negative.
-- whole (string or nil): nil or "" if no number before the fraction
-- numerator (string or nil): numerator, if any (default = 1 if a denominator is given)
-- denominator (string or nil): denominator, if any
-- sp_us (boolean): true if sp=us
-- negative_word (string): word to use for negative sign, if whole is empty
-- use_one (boolean): false: 2+1/2 → "two and a half"; true: "two and one-half"
local function fraction_to_english(whole, numerator, denominator, sp_us, negative_word, use_one)
if numerator or denominator then
local finished = (whole == nil or whole == '')
local sign = ''
if numerator then
if finished and numerator:sub(1, 1) == '-' then
numerator = numerator:sub(2)
sign = negative_word .. ' '
end
else
numerator = '1'
end
if not numerator:match('^%d+$') or not denominator or not denominator:match('^%d+$') then
return 'unsupported', ''
end
numerator = tonumber(numerator)
denominator = tonumber(denominator)
local dendata = denominators[denominator]
if not (dendata and 1 <= numerator and numerator <= 99) then
return 'unsupported', ''
end
local numstr, denstr
local sep = '-'
if numerator == 1 then
denstr = sp_us and dendata.us or dendata[1]
if finished or use_one then
numstr = 'one'
elseif denstr:match('^[aeiou]') then
numstr = 'an'
sep = ' '
else
numstr = 'a'
sep = ' '
end
else
numstr = numeral_to_english_less_100(numerator)
denstr = dendata.plural
if not denstr then
denstr = (sp_us and dendata.us or dendata[1]) .. 's'
end
end
if finished then
return 'finished', sign .. numstr .. sep .. denstr
end
return 'ok', ' and ' .. numstr .. sep .. denstr
end
return 'ok', ''
end  
-- Takes a decimal number and converts it to English text.
-- Return nil if a fraction cannot be converted (only some numbers are supported for fractions).
-- num (string or nil): the number to convert.
-- Can be an arbitrarily large decimal, such as "-123456789123456789.345", and
-- can use scientific notation (e.g. "1.23E5").
-- May fail for very large numbers not listed in "groups" such as "1E4000".
-- num is nil if there is no whole number before a fraction.
-- numerator (string or nil): numerator of fraction (nil if no fraction)
-- denominator (string or nil): denominator of fraction (nil if no fraction)
-- capitalize (boolean): whether to capitalize the result (e.g. 'One' instead of 'one')
-- use_and (boolean): whether to use the word 'and' between tens/ones place and higher places
-- hyphenate (boolean): whether to hyphenate all words in the result, useful as an adjective
-- ordinal (boolean): whether to produce an ordinal (e.g. 'first' instead of 'one')
-- plural (boolean): whether to pluralize the resulting number
-- links: nil: do not add any links; 'on': link "billion" and larger to Orders of magnitude article;
-- any other text: list of numbers to link (e.g. "billion,quadrillion")
-- negative_word: word to use for negative sign (typically 'negative' or 'minus'; nil to use default)
-- round: nil or '': no rounding; 'on': round to nearest two-word number; 'up'/'down': round up/down to two-word number
-- zero: word to use for value '0' (nil to use default)
-- use_one (boolean): false: 2+1/2 → "two and a half"; true: "two and one-half"