On 09/02/2017 11:02 AM, lithium iodate wrote:
> On Saturday, 2 September 2017 at 17:41:34 UTC, Ali Çehreli wrote:
>> You're right but I think there is no intention of interpreting the
>> result as UTF-8. "f62026" is just to be used as "f62026", which can be
>> converted byte-by-byte back to "ö…". That's how understand the
>> requirement anyway.
>>
>> Ali
>
> That is not possible, because you cannot know whether "f620" and "26" or
> "f6" and "2026" (or any other combination) should form a code point
> each. Additional padding to constant width (8 hex chars) is needed.
Ok, I see that I made a mistake but I still don't think the conversion
is one way. If we can convert byte-by-byte, we should be able to convert
back byte-by-byte, right? What I failed to ensure was to iterate by code
units. The following is able to get the same string back:
import std.stdio;
import std.string;
import std.algorithm;
import std.range;
import std.utf;
import std.conv;
auto toHex(R)(R input) {
// As Moritz Maxeiner says, this format is expensive
return input.byCodeUnit.map!(c => format!"%02x"(c)).joiner;
}
int hexValue(C)(C c) {
switch (c) {
case '0': .. case '9':
return c - '0';
case 'a': .. case 'f':
return c - 'a' + 10;
default:
assert(false);
}
}
auto fromHex(R, Dst = char)(R input) {
return input.chunks(2).map!((ch) {
auto high = ch.front.hexValue * 16;
ch.popFront();
return high + ch.front.hexValue;
}).map!(value => cast(Dst)value);
}
void main() {
assert("AAA".toHex.fromHex.equal("AAA"));
assert("ö…".toHex.fromHex.equal("ö…".byCodeUnit));
// Alternative check:
assert("ö…".toHex.fromHex.text.equal("ö…"));
}
Ali
