我在Lua中挣扎着浮点到十六进制转换。我的应用程序与旧的Akai S2000采样器进行通信。采样器将两个字节的消息编码为四个半字节值。半字节顺序相反，因此最重要的半字节是最后一个。有一个参数使用值的小数部分的二进制编码。两个MS半字节用于编码值的整数部分，LS半字节用于编码二进制分数。
基于此讨论https://bytes.com/topic/c/answers/219928-how-convert-float-hex我已经开始实现Lua算法，从给定的参数值生成这些半字节值。由于我的位计算不是那么强，我认为我做错了很多事情。应该有一种更简单的方法来计算这些值，并避免我的很多愚蠢的if / else黑客攻击。
我的代码（粘贴在下面）适用于正数，但负分数要难得多。
在我的测试中，我已添加到具有预期值的表中。每个表的工作方式如下：
key = give value * 100
value = expected outcome from my algorithm
即。 positiveNumbers表中的第一个条目表示输入值0.01，该值的预期输出是包含02 00 00 00的四字节MemoryBlock（前两个字节表示分数，后两个字节表示整数部分）。
目前我的算法在-0.94处失败，我无法破解它而不会破坏其他值。
是否有人通过位计算字符串，并且很容易看到我在转换负值时出现的任何noob错误？ 任何帮助或指示将不胜感激！
Lua Code：
function float2nibbles(value)
local nibbles = MemoryBlock(4, true)
-- Retreive integral and fraction parts of the given value to be converted
local integ, fract = math.modf(math.abs(value))
-- Calculate the values of the integral part (last two nibbles)
local bi = BigInteger(integ)
if value < 0 then
-- This variable is sometimes added in the negative conversion of the MS nibbles
local lsAdd = 1
if integ == 0 then
lsAdd = 0
end
nibbles:setByte(2, bit.band(bit.bnot(bi:getBitRangeAsInt(0,4)) + lsAdd, 0xF))
nibbles:setByte(3, bit.band(bit.bnot(bi:getBitRangeAsInt(4,4)), 0xF))
else
nibbles:setByte(2, bit.band(bi:getBitRangeAsInt(0,4), 0xF))
nibbles:setByte(3, bit.band(bi:getBitRangeAsInt(4,4), 0xF))
end
-- Calculate the values of the fraction (first two nibbles)
local remainder = fract
local prevRemain = 0
for i = 1,2 do
remainder = remainder * 16
-- Integral part of the remainder
local d = math.modf(remainder)
if value < 0 and fract ~= 0 then
local lsAdd = 1
if fract == 0 or i == 1 then
lsAdd = 0
end
console(string.format("lsAdd %d", lsAdd))
nibbles:setByte(2 - i, bit.band(bit.bnot(d) + lsAdd, 0xF))
else
nibbles:setByte(2 - i, bit.band(d, 0xF))
end
console(string.format("fract %d = %d, %.2f", i, d, remainder))
prevRemain = remainder
remainder = remainder - d
end
-- For some reason this increment helps when the LS nibble should increment the value of the second nibble
if nibbles:getByte(0) == 0 and nibbles:getByte(1) ~= 0 and value < 0 then
console(string.format("weird increment { %d %d }", nibbles:getByte(0), nibbles:getByte(1)))
nibbles:setByte(1, nibbles:getByte(1) + 1)
end
-- The precision of this data is one byte but apparently they seem to use a third increment to check for rounding
remainder = remainder * 16
console(string.format("final remainder %.2f", remainder))
if math.abs(remainder - prevRemain) > 0.001 and remainder > 14 then
console(string.format("overflow -> %.2f (%.2f)", remainder, prevRemain))
if value < 0 then
nibbles:setByte(0, nibbles:getByte(0) - 1)
else
nibbles:setByte(0, nibbles:getByte(0) + 1)
end
end
console(string.format("%.2f : integral part %s (%s), fract %.2f", value, bit.tohex(integ, 2), nibbles:toHexString(1), fract))
return nibbles
end
local positiveNumbers = {
"02 00 00 00",
"05 00 00 00",
"07 00 00 00",
"0A 00 00 00",
"0C 00 00 00",
"0F 00 00 00",
"02 01 00 00",
"04 01 00 00",
"07 01 00 00",
"09 01 00 00",
"0C 01 00 00",
"0E 01 00 00",
"01 02 00 00",
"03 02 00 00",
"06 02 00 00",
"09 02 00 00",
"0B 02 00 00",
"0E 02 00 00",
"00 03 00 00",
"03 03 00 00",
"05 03 00 00",
"08 03 00 00",
"0B 03 00 00",
"0D 03 00 00",
"00 04 00 00",
"02 04 00 00",
"05 04 00 00",
"07 04 00 00",
"0A 04 00 00",
"0C 04 00 00",
"0F 04 00 00",
"02 05 00 00",
"04 05 00 00",
"07 05 00 00",
"09 05 00 00",
"0C 05 00 00",
"0E 05 00 00",
"01 06 00 00",
"03 06 00 00",
"06 06 00 00",
"09 06 00 00",
"0B 06 00 00",
"0E 06 00 00",
"00 07 00 00",
"03 07 00 00",
"05 07 00 00",
"08 07 00 00",
"0B 07 00 00",
"0D 07 00 00",
"00 08 00 00",
"02 08 00 00",
"05 08 00 00",
"07 08 00 00",
"0A 08 00 00",
"0C 08 00 00",
"0F 08 00 00",
"02 09 00 00",
"04 09 00 00",
"07 09 00 00",
"09 09 00 00",
"0C 09 00 00",
"0E 09 00 00",
"01 0A 00 00",
"03 0A 00 00",
"06 0A 00 00",
"09 0A 00 00",
"0B 0A 00 00",
"0E 0A 00 00",
"00 0B 00 00",
"03 0B 00 00",
"05 0B 00 00",
"08 0B 00 00",
"0B 0B 00 00",
"0D 0B 00 00",
"00 0C 00 00",
"02 0C 00 00",
"05 0C 00 00",
"07 0C 00 00",
"0A 0C 00 00",
"0C 0C 00 00",
"0F 0C 00 00",
"02 0D 00 00",
"04 0D 00 00",
"07 0D 00 00",
"09 0D 00 00",
"0C 0D 00 00",
"0E 0D 00 00",
"01 0E 00 00",
"03 0E 00 00",
"06 0E 00 00",
"09 0E 00 00",
"0B 0E 00 00",
"0E 0E 00 00",
"00 0F 00 00",
"03 0F 00 00",
"05 0F 00 00",
"08 0F 00 00",
"0B 0F 00 00",
"0D 0F 00 00",
"00 00 01 00"
}
local negativeNumbers = {
"0E 0F 0F 0F",
"0B 0F 0F 0F",
"09 0F 0F 0F",
"06 0F 0F 0F",
"04 0F 0F 0F",
"01 0F 0F 0F",
"0E 0E 0F 0F",
"0C 0E 0F 0F",
"09 0E 0F 0F",
"07 0E 0F 0F",
"04 0E 0F 0F",
"02 0E 0F 0F",
"0F 0D 0F 0F",
"0D 0D 0F 0F",
"0A 0D 0F 0F",
"07 0D 0F 0F",
"05 0D 0F 0F",
"02 0D 0F 0F",
"00 0D 0F 0F",
"0D 0C 0F 0F",
"0B 0C 0F 0F",
"08 0C 0F 0F",
"05 0C 0F 0F",
"03 0C 0F 0F",
"00 0C 0F 0F",
"0E 0B 0F 0F",
"0B 0B 0F 0F",
"09 0B 0F 0F",
"06 0B 0F 0F",
"04 0B 0F 0F",
"01 0B 0F 0F",
"0E 0A 0F 0F",
"0C 0A 0F 0F",
"09 0A 0F 0F",
"07 0A 0F 0F",
"04 0A 0F 0F",
"02 0A 0F 0F",
"0F 09 0F 0F",
"0D 09 0F 0F",
"0A 09 0F 0F",
"07 09 0F 0F",
"05 09 0F 0F",
"02 09 0F 0F",
"00 09 0F 0F",
"0D 08 0F 0F",
"0B 08 0F 0F",
"08 08 0F 0F",
"05 08 0F 0F",
"03 08 0F 0F",
"00 08 0F 0F",
"0E 07 0F 0F",
"0B 07 0F 0F",
"09 07 0F 0F",
"06 07 0F 0F",
"04 07 0F 0F",
"01 07 0F 0F",
"0E 06 0F 0F",
"0C 06 0F 0F",
"09 06 0F 0F",
"07 06 0F 0F",
"04 06 0F 0F",
"02 06 0F 0F",
"0F 05 0F 0F",
"0D 05 0F 0F",
"0A 05 0F 0F",
"07 05 0F 0F",
"05 05 0F 0F",
"02 05 0F 0F",
"00 05 0F 0F",
"0D 04 0F 0F",
"0B 04 0F 0F",
"08 04 0F 0F",
"05 04 0F 0F",
"03 04 0F 0F",
"00 04 0F 0F",
"0E 03 0F 0F",
"0B 03 0F 0F",
"09 03 0F 0F",
"06 03 0F 0F",
"04 03 0F 0F",
"01 03 0F 0F",
"0E 02 0F 0F",
"0C 02 0F 0F",
"09 02 0F 0F",
"07 02 0F 0F",
"04 02 0F 0F",
"02 02 0F 0F",
"0F 01 0F 0F",
"0D 01 0F 0F",
"0A 01 0F 0F",
"07 01 0F 0F",
"05 01 0F 0F",
"02 01 0F 0F",
"00 01 0F 0F",
"0D 00 0F 0F",
"0B 00 0F 0F",
"08 00 0F 0F",
"05 00 0F 0F",
"03 00 0F 0F",
"00 00 0F 0F"
}
function verifyFloat2Nibbles(value, expectedMemBlock)
local temp = string.upper(float2nibbles(value):toHexString(1))
assert(expectedMemBlock == temp,
string.format("Incorrect result for %.2f, expected %s, got %s", value, expectedMemBlock, temp))
end
for k,v in pairs(positiveNumbers) do
verifyFloat2Nibbles(k / 100, v)
end
for k,v in pairs(negativeNumbers) do
verifyFloat2Nibbles((k / 100) * -1, v)
end
答案 0 :(得分：0)
你遇到的一个问题是，当你否定时，你不会将进位从一个半字节传播到另一个半字节。代码太复杂，无法审查和修复。这是一个重做：
n2a = {[0]='0','1','2','3','4','5','6','7','8','9','a','b','c','d','e','f'}
function f2h (f)
-- TODO should range check f
local scaledf = f * 256 -- move binary point 8 bits right
-- TODO optionally you could also round scaledf here
local scaledi = math.modf(scaledf) -- integer part
-- convert to nibbles
local scalediparts = { (0xf & scaledi),
(0xf & (scaledi >> 4)),
(0xf & (scaledi >> 8)),
(0xf & (scaledi >> 12)) }
-- output in hex
print(n2a[scalediparts[1]], n2a[scalediparts[2]], n2a[scalediparts[3]], n2a[scalediparts[4]])
-- return the nibbles
return scalediparts
end
和控制台测试：
> f2h(-0.01)
e f f f
table: 0x7feaf9d06390
> f2h(-0.94)
0 1 f f
table: 0x7feaf9e009a0
> f2h(0.01)
2 0 0 0
table: 0x7feaf9d06410
>
这是使用Lua 5.3位运算符;转换到bit库非常简单。您还需要修改print语句并返回值以符合您的偏好。
答案 1 :(得分：0)
function float2nibbles(value)
local nibbles = MemoryBlock(4, true)
local n = math.floor(math.abs(value)*256 + 0.13)
n = value < 0 and 0x10000 - n or n
for pos = 0, 3 do
nibbles:setByte(pos, n%16)
n = math.floor(n/16)
end
return nibbles
end