Convert signed IEEE 754 float to hexadecimal representation

Question

I am using front-end Lua, which, unfortunately, is deprecated, so I am stuck here with version 5.1, which means that the bit32 library bit32 not available (which I probably could use to convert it).

So, I am wondering if anyone knows how I could implement a floating point function to binary (digit) or, even better, floating point to hex. The best I managed to come up with is the binary / hex decimal function ...

Answer 1

The following functions use some code from François Perrad lua-MessagePack . Thanks a lot to him.

 function float2hex (n) if n == 0.0 then return 0.0 end local sign = 0 if n < 0.0 then sign = 0x80 n = -n end local mant, expo = math.frexp(n) local hext = {} if mant ~= mant then hext[#hext+1] = string.char(0xFF, 0x88, 0x00, 0x00) elseif mant == math.huge or expo > 0x80 then if sign == 0 then hext[#hext+1] = string.char(0x7F, 0x80, 0x00, 0x00) else hext[#hext+1] = string.char(0xFF, 0x80, 0x00, 0x00) end elseif (mant == 0.0 and expo == 0) or expo < -0x7E then hext[#hext+1] = string.char(sign, 0x00, 0x00, 0x00) else expo = expo + 0x7E mant = (mant * 2.0 - 1.0) * math.ldexp(0.5, 24) hext[#hext+1] = string.char(sign + math.floor(expo / 0x2), (expo % 0x2) * 0x80 + math.floor(mant / 0x10000), math.floor(mant / 0x100) % 0x100, mant % 0x100) end return tonumber(string.gsub(table.concat(hext),"(.)", function (c) return string.format("%02X%s",string.byte(c),"") end), 16) end function hex2float (c) if c == 0 then return 0.0 end local c = string.gsub(string.format("%X", c),"(..)",function (x) return string.char(tonumber(x, 16)) end) local b1,b2,b3,b4 = string.byte(c, 1, 4) local sign = b1 > 0x7F local expo = (b1 % 0x80) * 0x2 + math.floor(b2 / 0x80) local mant = ((b2 % 0x80) * 0x100 + b3) * 0x100 + b4 if sign then sign = -1 else sign = 1 end local n if mant == 0 and expo == 0 then n = sign * 0.0 elseif expo == 0xFF then if mant == 0 then n = sign * math.huge else n = 0.0/0.0 end else n = sign * math.ldexp(1.0 + mant / 0x800000, expo - 0x7F) end return n end 

Answer 2

In the above example, float2hex returns int. This, if someone needs it, is the intToHex conversion function, which can be found in the lua archives ( http://lua-users.org/lists/lua-l/2004-09/msg00054.html ). I used the return value of the float2hex function above and passed it to this function. The output of intToHex is a string (Ex: 0xA4CD).

 function intToHex(IN) local B,K,OUT,I,D=16,"0123456789ABCDEF","",0 while IN>0 do I=I+1 IN,D=math.floor(IN/B),math.mod(IN,B)+1 OUT=string.sub(K,D,D)..OUT end OUT = "0x" .. OUT return OUT end 

Answer 3

The problem I ran into was converting from Hex back to Float; You can use this tomometer (x, 16) to convert it in conjunction with the answer “Error - parsing”. String.sub is only there because my Modbus driver does not change bytes :)

 function convertFloatSwapWord(number) -- number is string of format = 0x######## local x = 0 x = float2hex(number) x = intToHex(x) x = string.sub(x,5,6) .. string.sub(x,3,4) .. string.sub(x,9,10) .. string.sub(x,7,8) x = hex2float(tonumber(x, 16)) return x end