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http://issues.apache.org/jira/browse/LUCENE-467?page=comments#action_12357851 ]
Yonik Seeley commented on LUCENE-467:
-------------------------------------
Fun with premature optimization!
I know this isn't a bottleneck, but here is the fastest floatToByte() that I
could come up with:
public static byte floatToByte(float f) {
int bits = Float.floatToRawIntBits(f);
if (bits<=0) return 0;
int mantissa = (bits & 0xffffff) >> 21;
int exponent = (bits >>> 24) - 63 + 15;
if ((exponent & ~0x1f)==0) return (byte)((exponent << 3) | mantissa);
else if (exponent<0) return 1;
return -1;
}
Here is the original from Lucene for reference:
public static byte floatToByte(float f) {
if (f < 0.0f) // round negatives up to zero
f = 0.0f;
if (f == 0.0f) // zero is a special case
return 0;
int bits = Float.floatToIntBits(f); // parse float into parts
int mantissa = (bits & 0xffffff) >> 21;
int exponent = (((bits >> 24) & 0x7f) - 63) + 15;
if (exponent > 31) { // overflow: use max value
exponent = 31;
mantissa = 7;
}
if (exponent < 0) { // underflow: use min value
exponent = 0;
mantissa = 1;
}
return (byte)((exponent << 3) | mantissa); // pack into a byte
}
Here is the performance (in seconds) on my P4 to do 640M conversions:
JDK14-server JDK14-client JDK15-server JDK15-client
JDK16-server JDK16-client
orig 75.422 89.451 8.344 57.631
7.656 57.984
new 67.265 78.891 5.906 22.172
5.172 18.750
diff 12% 13% 41%
160% 48% 209%
Some decent gains... but the biggest moral of the story is: use Java>=1.5 and
-server if you can!
> 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.
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