Function to decode *valid* UTF-8

This commit is contained in:
Ferdinand Majerech 2014-07-29 01:58:59 +02:00
parent 53b39dc590
commit cf15d55da0

View file

@ -356,6 +356,63 @@ ValidateResult validateUTF8NoGC(const(char[]) str) @trusted pure nothrow @nogc
return ValidateResult(true); return ValidateResult(true);
} }
/// @nogc version of std.utf.decode() for (char[]), but assumes str is valid UTF-8.
///
/// The caller $(B must) handle ASCII (< 0x80) characters manually; this is asserted to
/// force code using this function to be efficient.
///
/// Params:
///
/// str = Will decode the first code point from this string. Must be valid UTF-8,
/// otherwise undefined behavior WILL occur.
/// index = Index in str where the code point starts. Will be updated to point to the
/// next code point.
dchar decodeValidUTF8NoGC(const(char[]) str, ref size_t index)
@trusted pure nothrow @nogc
{
/// Dchar bitmask for different numbers of UTF-8 code units.
enum bitMask = [(1 << 7) - 1, (1 << 11) - 1, (1 << 16) - 1, (1 << 21) - 1];
auto pstr = str.ptr + index;
immutable length = str.length - index;
ubyte fst = pstr[0];
assert(fst & 0x80);
ubyte tmp = void;
dchar d = fst; // upper control bits are masked out later
fst <<= 1;
enum invalidUTFMsg = "Invalid UTF-8 sequence in supposedly validated string";
foreach (i; TypeTuple!(1, 2, 3))
{
assert(i != length, "Decoding out of bounds in supposedly validated UTF-8");
tmp = pstr[i];
assert((tmp & 0xC0) == 0x80, invalidUTFMsg);
d = (d << 6) | (tmp & 0x3F);
fst <<= 1;
if (!(fst & 0x80)) // no more bytes
{
d &= bitMask[i]; // mask out control bits
// overlong, could have been encoded with i bytes
assert((d & ~bitMask[i - 1]) != 0, invalidUTFMsg);
// check for surrogates only needed for 3 bytes
static if (i == 2) { assert(isValidDchar(d), invalidUTFMsg); }
index += i + 1;
static if (i == 3) { assert(d <= dchar.max, invalidUTFMsg); }
return d;
}
}
assert(false, invalidUTFMsg);
}
/// @nogc version of std.utf.isValidDchar /// @nogc version of std.utf.isValidDchar
bool isValidDchar(dchar c) @safe pure nothrow @nogc bool isValidDchar(dchar c) @safe pure nothrow @nogc
{ {