Fix Math.round in runtime.cc and x64 optimized code.

Fix Math.round in runtime.cc and x64 optimized code.

Make math-round.js test check both normal and optimized version.
Add some cases to the tests.

BUG=v8:958
TEST=mjsunit/math-round

Committed: http://code.google.com/p/v8/source/detail?r=7599

[William Hesse, 2011-04-13 09:12:45]

LGTM.

http://codereview.chromium.org/6837018/diff/1/src/x64/lithium-codegen-x64.cc
File src/x64/lithium-codegen-x64.cc (right):

http://codereview.chromium.org/6837018/diff/1/src/x64/lithium-codegen-x64.cc#...
src/x64/lithium-codegen-x64.cc:2733: // rounding, due to loss of precission, but
only for a number that's
precision

http://codereview.chromium.org/6837018/diff/1/test/mjsunit/math-round.js
File test/mjsunit/math-round.js (right):

http://codereview.chromium.org/6837018/diff/1/test/mjsunit/math-round.js#newc...
test/mjsunit/math-round.js:34: assertEquals(expect, doRound(input));
assertEquals(1/expect, 1/doRound(input));
You can probably also leave out the normal comparison - the 1/x comparison
includes that case except for +- infinity.

http://codereview.chromium.org/6837018/diff/1/test/mjsunit/math-round.js#newc...
test/mjsunit/math-round.js:50: testRound(-0, -0.5);
To test for -0, you must compare 1/-0 to 1/result, otherwise -0 == 0.

[Lasse Reichstein, 2011-04-13 09:35:23]

http://codereview.chromium.org/6837018/diff/1/src/x64/lithium-codegen-x64.cc
File src/x64/lithium-codegen-x64.cc (right):

http://codereview.chromium.org/6837018/diff/1/src/x64/lithium-codegen-x64.cc#...
src/x64/lithium-codegen-x64.cc:2733: // rounding, due to loss of precission, but
only for a number that's
Fixed, thanks.

http://codereview.chromium.org/6837018/diff/1/test/mjsunit/math-round.js
File test/mjsunit/math-round.js (right):

http://codereview.chromium.org/6837018/diff/1/test/mjsunit/math-round.js#newc...
test/mjsunit/math-round.js:34: assertEquals(expect, doRound(input));
Not necessary, assertEquals correctly distinguishes 0 and -0 since revision
7368.

http://codereview.chromium.org/6837018/diff/1/test/mjsunit/math-round.js#newc...
test/mjsunit/math-round.js:50: testRound(-0, -0.5);
Not any more.