That looks good. I'm just worried about the jump forward - ideally the
case c < 127 would simply entail a quick return. I tried a fix, but it
didn't do what I wanted in ldc. We shouldn't assert(0) if wrong - just
skip one byte. Also, are we right to not worry about 5- and 6-byte
sequences? The docs keep on threatening with it, and then immediately
mention those are not valid.
void popFront3(ref char[] s) @trusted pure nothrow {
immutable c = s[0];
uint char_length = 1;
if (c < 127)
{
Lend :
s = s.ptr[char_length .. s.length];
} else {
if (c < 192)
{
char_length = 2;
goto Lend;
}
if (c < 240) {
char_length = 3;
goto Lend;
}
if (c < 248) {
char_length = 4;
}
goto Lend;
}
}
Andrei
On 10/10/16 9:39 PM, Stefan Koch wrote:
This version has 24 instructions but these have a smaller encoding then
and are generally inexpensive
With inline asm and conditional moves it would be possible to reduce
this even further
to ~20 instructions.
void popFront1(ref char[] s) @trusted pure nothrow {
immutable c = s[0];
size_t char_length = 1;
if (c < 127)
{
goto Lend;
} else {
if ((c & 0b1100_0000) == 0b1000_0000)
{
// This is invalid as a first char
goto Lerror;
}
if (c < 192)
{
char_length = 2;
goto Lend;
}
if (c < 240) {
char_length = 3;
goto Lend;
}
if (c < 248) {
char_length = 4;
goto Lend;
}
//These characters are also no longer valid
Lerror : assert(0);
}
Lend :
s = s.ptr[char_length .. s.length];
}