[
http://issues.apache.org/jira/browse/LUCENE-467?page=comments#action_12357911 ]
Yonik Seeley commented on LUCENE-467:
-------------------------------------
Here is a new version that's faster by keeping the mantissa and exponent
together. It's fast-path does a single shift and a single add after
getting the float bits.
public byte floatToByte(float f) {
int bits = Float.floatToRawIntBits(f);
int smallfloat = bits >> 21; // only keep 3 highest bits in mantissa
if (smallfloat < (63-15)<<3) {
return (bits<=0) ? (byte)0 : (byte)1; // 0 or underflow
}
if (smallfloat >= ((63-15)+32)<<3) {
return -1; // overflow
}
return (byte)(smallfloat - ((63-15)<<3));
}
---JVM--- -CUR-- -NEW-- -DIFF-
14-server 75.422 66.515 13%
14-client 89.451 79.734 12%
15-server 8.344 3.859 116%
15-client 57.631 17.031 238%
16-server 7.656 3.172 141%
16-client 57.984 16.531 251%
These numbers include the overhead of a float loop and the method
call overhead.
> Use Float.floatToRawIntBits over Float.floatToIntBits
> -----------------------------------------------------
>
> Key: LUCENE-467
> URL: http://issues.apache.org/jira/browse/LUCENE-467
> Project: Lucene - Java
> Type: Improvement
> Components: Other
> Versions: 1.9
> Reporter: Yonik Seeley
> Priority: Minor
>
> Copied From my Email:
> Float.floatToRawIntBits (in Java1.4) gives the raw float bits without
> normalization (like *(int*)&floatvar would in C). Since it doesn't do
> normalization of NaN values, it's faster (and hopefully optimized to a
> simple inline machine instruction by the JVM).
> On my Pentium4, using floatToRawIntBits is over 5 times as fast as
> floatToIntBits.
> That can really add up in something like Similarity.floatToByte() for
> encoding norms, especially if used as a way to compress an array of
> float during query time as suggested by Doug.
--
This message is automatically generated by JIRA.
-
If you think it was sent incorrectly contact one of the administrators:
http://issues.apache.org/jira/secure/Administrators.jspa
-
For more information on JIRA, see:
http://www.atlassian.com/software/jira
---------------------------------------------------------------------
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]
