Fix Issue 8259: dart:math pow broken for large integers.

Fix Issue 8259:	dart:math pow broken for large integers.
Committed: https://code.google.com/p/dart/source/detail?r=18150

[Vyacheslav Egorov (Google), 2013-02-05 00:34:36]

https://codereview.chromium.org/12180022/diff/1/runtime/lib/double.cc
File runtime/lib/double.cc (right):

https://codereview.chromium.org/12180022/diff/1/runtime/lib/double.cc#newcode84
runtime/lib/double.cc:84: if ((int64_val ==
static_cast<int64_t>(0x8000000000000000LL)) &&
I don't think we can do this.

If a truncated double is not representable in an integer then behavior is
undefined per C++ Standard. Thus we can't rely on it returning the same marker
as Intel instruction use. (see [conv.fpint] in the Standard)

Here is another idea: Mint/Smi::kMinValue is representable in a double and so is
Mint/Smi::kMaxValue + 1 (cause both are powers of two).

If you declare MaxValuePlusOneAsDouble constants then you should be able to use

(X::kMinValue <= val) && (val < X::kMaxValuePlusOneAsDouble) 

to determine whether result of a conversion fits into an X or not.

[srdjan, 2013-02-05 00:55:58]

Simplified by using BigintOperations. TODO: cleanup BigintOperations::ToMint to
return Mint instead of int64_t .

PTAL

[Vyacheslav Egorov (Google), 2013-02-05 17:30:28]

LGTM

https://codereview.chromium.org/12180022/diff/5001/runtime/lib/double.cc
File runtime/lib/double.cc (right):

https://codereview.chromium.org/12180022/diff/5001/runtime/lib/double.cc#newc...
runtime/lib/double.cc:83: if (BigintOperations::FitsIntoSmi(big)) return
BigintOperations::ToSmi(big);
This code is hard to read. Can you make it 

if (...) {
  return ...;
} else if (...) {
  return ...;
}

[srdjan, 2013-02-05 18:04:08]

https://codereview.chromium.org/12180022/diff/5001/runtime/lib/double.cc
File runtime/lib/double.cc (right):

https://codereview.chromium.org/12180022/diff/5001/runtime/lib/double.cc#newc...
runtime/lib/double.cc:83: if (BigintOperations::FitsIntoSmi(big)) return
BigintOperations::ToSmi(big);
On 2013/02/05 17:30:28, Vyacheslav Egorov (Google) wrote:
> This code is hard to read. Can you make it 
> 
> if (...) {
>   return ...;
> } else if (...) {
>   return ...;
> }

Done.