Hi Brett,
Extra care is needed if the input array might be modified concurrently
with the method execution.
When control flow decisions are made based on array contents, the
integrity of the result depends on reading each byte of the array
exactly once.
Regards, Roger
On 7/27/25 4:45 PM, Brett Okken wrote:
In String.encodeUTF8, when the coder is latin1, there is a call to
StringCoding.hasNegatives to determine if any special handling is
needed. If not, a clone of the val is returned.
If there are negative values, it then loops, from the beginning,
through all the values to handle any individual negative values.
Would it be better to call StringCoding.countPositives? If the result
equals the length, the clone can still be returned. But if it does
not, all the values which are positive can be simply copied to the
target byte[] and only values beyond that point need to be checked again.
https://github.com/openjdk/jdk/blob/master/src/java.base/share/classes/java/lang/String.java#L1287-L1300
if (!StringCoding.hasNegatives(val, 0, val.length)) {
return val.clone();
}
int dp = 0;
byte[] dst = StringUTF16.newBytesFor(val.length);
for (byte c : val) {
if (c < 0) {
dst[dp++] = (byte) (0xc0 | ((c & 0xff) >> 6));
dst[dp++] = (byte) (0x80 | (c & 0x3f));
} else {
dst[dp++] = c;
}
}
Can be changed to look like:
int positives = StringCoding.countPositives(val, 0, val.length);
if (positives == val.length) {
return val.clone();
}
int dp = positives;
byte[] dst = StringUTF16.newBytesFor(val.length);
if (positives > 0) {
System.arraycopy(val, 0, dst, 0, positives);
}
for (int i=dp; i<val.length; ++i) {
byte c = val[i];
if (c < 0) {
dst[dp++] = (byte) (0xc0 | ((c & 0xff) >> 6));
dst[dp++] = (byte) (0x80 | (c & 0x3f));
} else {
dst[dp++] = c;
}
}
I have done a bit of testing with the StringEncode jmh benchmark on my
local windows device.
encodeLatin1LongEnd speeds up significantly (~70%)
encodeLatin1LongStart slows down (~20%)
encodeLatin1Mixed speeds up by ~30%
The remaining tests do not show much difference either way.
Brett
