Convert number to float in bytes - serialization

Question

I know that lua uses double precision number formats so I wonder if there is a way to convert number directly into string as float value (4 bytes) so that I could send it over udp socket

Answer 1

For Lua 5.3+
local function float32_binary_dump(value)
return ("<f"):pack(value)
end
For Lua 5.1+
local function float32_binary_dump(value)
local img, s, h, d = 2^32 - 2^22, "", 1
if value == value then
img = 2^31 - 2^23
if value < 0 or value == 0 and 1/value < 0 then
value, img = -value, 2^32 - 2^23
end
if value > 0.5 * 2^-149 and value < 2^128 then
-- rounding 64-bit double to 32-bit float
d = math.floor(math.log(value)/math.log(2) + 0.5)
d = value < 2^d and d - 1 or d
local e = 2^(d < -126 and -149 or d - 23)
value = value + 0.5 * e
local r = value % e
value = value - (r == 0 and value % (e + e) or r)
end
-- dumping 32-bit image of float
if value < 2^-149 then
img = img - (2^31 - 2^23)
elseif value <= 2^128 - 2^104 then
if d < -126 then
d, h = -126, 0
end
img = img + (value / 2^d + (d - (-126)) * h - 255) * 2^23
end
end
-- convert 32-bit image to little-endian string
while #s < 4 do
local b = img % 256
s = s..string.char(b)
img = (img - b) / 256
end
return s
end