Code review request for 6908131 Pure Java implementations of StrictMath.floor(double) &StrictMath.ceil(double)

[Dmitry Nadezhin]

Martin, Thank you for the answer.

I found your benchmark in "jdk/test/java/util/ArrayList".
Also I see an example of microbenchmark included in the post to 
core-libs-dev:
http://mail.openjdk.java.net/pipermail/core-libs-dev/2009-November/003226.html 
.

Its nice to keep such microbenchmarks in jdk/tests. When there are 
variants of method implementation,
the choice of fastest method is not forever. The choice can change later 
after optimizations in HotSpot.

For example, floor and ceil results on pattern3 = { 0.1, -0.1, 1e4+0.1, 
-1e4-0.1, 1e8+0.1, -1e8-0.1, 1e12+0.1, -1e12-0.1, (1L<<52)/1.1, 
-(1L<<52)/1.1};

jdk1.5.0_21/bin/java -d32 -server
empty                took       1,67 nsec
Math.ceil            took      65,53 nsec 
Math.floor           took      66,62 nsec
StrictMath.ceil      took      67,21 nsec 
StrictMath.floor     took      66,04 nsec
FloorCeilDarcy.ceil  took      24,22 nsec 
FloorCeilDarcy.floor took      23,36 nsec
FloorCeilHain.ceil   took      97,61 nsec 
FloorCeilHain.floor  took     100,56 nsec

jdk1.5.0_21/bin/java -d64 -server
empty                took       1,67 nsec
Math.ceil            took      33,53 nsec 
Math.floor           took      33,54 nsec
StrictMath.ceil      took      33,53 nsec 
StrictMath.floor     took      33,54 nsec
FloorCeilDarcy.ceil  took       8,18 nsec 
FloorCeilDarcy.floor took      16,96 nsec
FloorCeilHain.ceil   took      20,39 nsec 
FloorCeilHain.floor  took      19,92 nsec


jdk1.7.0_b79/bin/java -d32 -server
empty                took       1,67 nsec
Math.ceil            took      15,74 nsec 
Math.floor           took      14,70 nsec
StrictMath.ceil      took      15,76 nsec 
StrictMath.floor     took      14,70 nsec
FloorCeilDarcy.ceil  took      15,88 nsec 
FloorCeilDarcy.floor took      14,98 nsec
FloorCeilHain.ceil   took      12,27 nsec 
FloorCeilHain.floor  took      10,38 nsec

jdk1.7.0_b79/bin/java -d64 -server
empty                took       1,67 nsec
Math.ceil            took       7,66 nsec 
Math.floor           took       7,81 nsec
StrictMath.ceil      took       7,65 nsec 
StrictMath.floor     took       7,80 nsec
FloorCeilDarcy.ceil  took       7,62 nsec 
FloorCeilDarcy.floor took       7,80 nsec
FloorCeilHain.ceil   took      12,65 nsec 
FloorCeilHain.floor  took      11,15 nsec


On JDK-1.5, Darcy's implementation was much faster than Hain's.
On JDK-1.7 -d32 -server, Hain's implementation is faster than Darcy's.
Perhaps implementation which are not the best choice now may become the 
best choice later.
Perhaps alternative implementation should be stored somewhere too.
This maybe a project in OpenJdk or a subproject of other project.
I shall write something about it in the next message with a new subject.

  -Dima