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Fix math.fround

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This commit is contained in:
Lars Mueller 2023-02-26 15:39:37 +01:00
parent c5e622f4a9
commit fdfe65167f
1 changed files with 12 additions and 5 deletions
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17
math.lua
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@ -152,6 +152,9 @@ function tostring(number, base, digit_function, precision)
end end
-- See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/fround#polyfill -- See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Math/fround#polyfill
-- Rounds a 64-bit float to a 32-bit float;
-- if the closest 32-bit float is out of bounds,
-- the appropriate infinity is returned.
function fround(number) function fround(number)
if number == 0 or number ~= number then if number == 0 or number ~= number then
return number return number
@ -161,14 +164,18 @@ function fround(number)
sign = -1 sign = -1
number = -number number = -number
end end
local exp = math_floor(math.log(number, 2)) local _, exp = math.frexp(number)
exp = exp - 1 -- we want 2^exponent >= number > 2^(exponent-1)
local powexp = 2 ^ math.max(-126, math.min(exp, 127)) local powexp = 2 ^ math.max(-126, math.min(exp, 127))
local leading = exp < -127 and 0 or 1 local leading = exp <= -127 and 0 or 1 -- subnormal number?
local mantissa = math_floor((leading - number / powexp) * 0x800000 + 0.5) local mantissa = math.floor((number / powexp - leading) * 0x800000 + 0.5)
if mantissa <= -0x800000 then if
mantissa > 0x800000 -- doesn't fit in mantissa
or (exp >= 127 and mantissa == 0x800000) -- fits if the exponent can be increased
then
return sign * inf return sign * inf
end end
return sign * powexp * (leading - mantissa / 0x800000) return sign * powexp * (leading + mantissa / 0x800000)
end end
-- Export environment -- Export environment