Re: converting arbitrary long decimals to hex?
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- Subject: Re: converting arbitrary long decimals to hex?
- From: Norbert Kiesel <nkiesel@...>
- Date: 2010年1月08日 10:15:05 -0800
On Sat, 2010年01月09日 at 02:04 +0800, KHMan wrote:
> Norbert Kiesel wrote:
> > [snip]
> > function tohex(decimal)
> > if type(decimal) == 'number' or #decimal < 15 then
> > return ('%x'):format(decimal)
> > end
> > local hex = ''
> > while decimal do
> > local div = ''
> > local mod = 0
> > for i = 1, #decimal do
> > mod = mod * 10 + tonumber(decimal:sub(i, i))
> > local f = math.floor(mod / 16)
> > mod = mod - f * 16
> > div = div .. f
> > end
> > hex = ('%x'):format(mod) .. hex
> > decimal = div:match('0+(.+)')
> > end
> >
> > return hex
> > end
>
> Oh sorry, ha ha, I failed to see the nested loop. ;-)
>
> It looks real slow... :-)
>
Yeah, tabs went missing. I include an untabbed version below (otherwise
unchanged). Regarding the "real slow": it is guaranteed to decrease the
length of the decimal every round (due to the div:match() at the
bottom), so it's O(n^2). Can you come up with something better?
</nk>
function tohex(decimal)
if type(decimal) == 'number' or #decimal < 15 then
return ('%x'):format(decimal)
end
local hex = ''
while decimal do
local div = ''
local mod = 0
for i = 1, #decimal do
mod = mod * 10 + tonumber(decimal:sub(i, i))
local f = math.floor(mod / 16)
mod = mod - f * 16
div = div .. f
end
hex = ('%x'):format(mod) .. hex
decimal = div:match('0+(.+)')
end
return hex
end