Optimize number-to-string conversions.

Optimize number-to-string conversions.

Add lookup table for ints in [-99, 99] and a cache for doubles.

R=iposva@google.com

Committed: https://code.google.com/p/dart/source/detail?r=39710

[Ivan Posva, 2014-08-29 20:58:47]

LGTM -ip

https://codereview.chromium.org/518093002/diff/120001/runtime/lib/double.dart
File runtime/lib/double.dart (right):

https://codereview.chromium.org/518093002/diff/120001/runtime/lib/double.dart...
runtime/lib/double.dart:140: static const int CACHE_LENGTH = 16;
How about enforcing the comment by:
static const int CACHE_SIZE_LOG2 = 3;
static const int CACHE_LENGTH = 1 << (CACHE_SIZE_LOG2 + 1);
...

https://codereview.chromium.org/518093002/diff/120001/runtime/lib/integers.dart
File runtime/lib/integers.dart (right):

https://codereview.chromium.org/518093002/diff/120001/runtime/lib/integers.da...
runtime/lib/integers.dart:319: "91", "92", "93", "94", "95", "96", "97", "98",
"99",
Trailing comma.

[koda, 2014-08-29 21:02:33]

https://codereview.chromium.org/518093002/diff/120001/runtime/lib/double.dart
File runtime/lib/double.dart (right):

https://codereview.chromium.org/518093002/diff/120001/runtime/lib/double.dart...
runtime/lib/double.dart:140: static const int CACHE_LENGTH = 16;
On 2014/08/29 20:58:47, Ivan Posva wrote:
> How about enforcing the comment by:
> static const int CACHE_SIZE_LOG2 = 3;
> static const int CACHE_LENGTH = 1 << (CACHE_SIZE_LOG2 + 1);
> ...

Done.

https://codereview.chromium.org/518093002/diff/120001/runtime/lib/integers.dart
File runtime/lib/integers.dart (right):

https://codereview.chromium.org/518093002/diff/120001/runtime/lib/integers.da...
runtime/lib/integers.dart:319: "91", "92", "93", "94", "95", "96", "97", "98",
"99",
On 2014/08/29 20:58:47, Ivan Posva wrote:
> Trailing comma.

Done.

[koda, 2014-08-29 21:13:36]

Committed patchset #7 (id:120001) manually as r39710 (presubmit successful).

[Lasse Reichstein Nielsen, 2014-09-01 07:14:20]

lrn@google.com changed reviewers:
+ lrn@google.com

[Lasse Reichstein Nielsen, 2014-09-01 07:14:21]

https://codereview.chromium.org/518093002/diff/120001/runtime/lib/double.dart
File runtime/lib/double.dart (right):

https://codereview.chromium.org/518093002/diff/120001/runtime/lib/double.dart...
runtime/lib/double.dart:144: static int _cacheEvictIndex = 0;
This "optimization" seems a little too speculative to me.
Are there cases, outside of silly benchmarks, where the same four doubles keep
getting toString'ed? If so, is it always the same doubles (e.g., -1.0, 0.0, 1.0,
and 2.0) so we could just hardcode those?

https://codereview.chromium.org/518093002/diff/120001/runtime/lib/integers.dart
File runtime/lib/integers.dart (right):

https://codereview.chromium.org/518093002/diff/120001/runtime/lib/integers.da...
runtime/lib/integers.dart:319: "91", "92", "93", "94", "95", "96", "97", "98",
"99",
There isn't anything inherently wrong with a trailing comma in Dart. I would
actually prefer it for "tables" like this one, because it makes it easier to add
more lines or rearrange lines.
(But this is VM code, so do go with the VM preferred style here).

https://codereview.chromium.org/518093002/diff/120001/runtime/lib/integers.da...
runtime/lib/integers.dart:349: if (this < 100 && this > -100) return
_smallLookupTable[this + 99];
Would it make sense to put this after the sign check?
Then we would have:
  if (this < 0) return _negativeToString(this);
  if (this < 100) return _posSmallLookupTable[this];
and in _negativeToSTring
  if (this > -100) return _negSmallLookupTable[this + 99];

It seems to have one less test for the positive case (but then, -99..99 test can
be done in one compare by a good compiler).
I.e., do we have a benchmark that can see what is best?