Albert, this code is a really faster (3 sec versus 120 sec).
Unfortunately, my strings can contain more than 65000 '%'s.
What to do in this case ?

>Assuming fewer than 65000 '%'s :
>
>

>#define STRING_LEN	500	&& * 1024
>#define LOOP_COUNT	11
>
>lcURL = ""
>for i = 1 to STRING_LEN
>	lcURL = lcURL + "%" + right(transform(i % 256, "@0"), 2) + replicate("X", 1022)
>endfor
>
>clear
>
>ss1 = seconds()
>for i = 1 to LOOP_COUNT
>	lcResult1 = URLDecode1(lcURL)
>endfor
>? seconds() - ss1
>
>ss1 = seconds()
>for i = 1 to LOOP_COUNT
>	lcResult2 = URLDecode2(lcURL)
>endfor
>? seconds() - ss1
>
>? lcResult1 == lcResult2
>? len(lcResult1), len(lcResult2)
>
>function URLDecode1
>	*** URLDecodes a text string:
>	* Replaces %hh tokens with ascii characters
>
>	*** Input: tcInput - Text string to decode
>	*** Return: Decoded string
>	* Author: Nick
>
>	lparameter tcInput
>
>	local lnPcntPos, lcOutput
>	lcOutput=""
>	tcInput=strtran(tcInput, "+", " ")
>
>	do while !empty(tcInput)
>		lnPcntPos=at("%",tcInput)
>		if betw( lnPcntPos, 1, len(tcInput)-2 )
>			lcOutput= m.lcOutput+ left(tcInput, ;
>				lnPcntPos-1)+chr(eval('0x'+substr(tcInput,lnPcntPos+1,2)))
>			tcInput=substr(tcInput,lnPcntPos+3)
>		else
>			lcOutput=m.lcOutput+ m.tcInput
>			exit
>		endif
>	enddo
>	return lcOutput
>
>function URLDecode2
>	*** URLDecodes a text string:
>	* Replaces %hh tokens with ascii characters
>
>	*** Input: tcInput - Text string to decode
>	*** Return: Decoded string
>	* Author: Albert
>
>	lparameter tcInput
>
>	local lnPcntPos, lcOutput, lnPcntCount, i
>	tcInput = strtran(tcInput, "+", " ")
>
>	local array laPercents[1]
>	lnPcntCount = alines(laPercents, strtran(tcInput, "%", chr(13)))
>
>	lcOutput = laPercents[1]
>	
>	for i = 2 to lnPcntCount
>		lcOutput = m.lcOutput + chr(evaluate('0x' + left(laPercents[i], 2))) + ;
>			substr(laPercents[i], 3)
>	endfor
>	return lcOutput
>