MIPS: Fix rounding in Uint8ClampedArray setter.

MIPS: Fix rounding in Uint8ClampedArray setter.

Port r12364 (31e40def)

Original commit message:
According to Web IDL spec, we should round to
the nearest integer, choosing the even integer
if it lies halfway between two.

BUG=
TEST=

Committed: https://code.google.com/p/v8/source/detail?r=12380

[ulan, 2012-08-24 07:21:07]

https://chromiumcodereview.appspot.com/10870049/diff/1/src/mips/simulator-mip...
File src/mips/simulator-mips.cc (right):

https://chromiumcodereview.appspot.com/10870049/diff/1/src/mips/simulator-mip...
src/mips/simulator-mips.cc:2073: double rounded = fs > 0 ? floor(fs + 0.5) :
ceil(fs - 0.5);
Why not just do floor(fs + 0.5) for both positive and negative values?

https://chromiumcodereview.appspot.com/10870049/diff/1/src/mips/simulator-mip...
src/mips/simulator-mips.cc:2075: if ((result & 1) != 0 && result - fs == 0.5) {
This doesn't handle the case when fs is negative, e.g. fs == -4.5, result == -5,
result-fs == -0.5.

[palfia, 2012-08-24 23:57:28]

Thanks for your corrections, I've uploaded a new patchset, which fixes the
rounding of negative numbers.

https://chromiumcodereview.appspot.com/10870049/diff/1/src/mips/simulator-mip...
File src/mips/simulator-mips.cc (right):

https://chromiumcodereview.appspot.com/10870049/diff/1/src/mips/simulator-mip...
src/mips/simulator-mips.cc:2073: double rounded = fs > 0 ? floor(fs + 0.5) :
ceil(fs - 0.5);
On 2012/08/24 07:21:07, ulan wrote:
> Why not just do floor(fs + 0.5) for both positive and negative values?

Done.

https://chromiumcodereview.appspot.com/10870049/diff/1/src/mips/simulator-mip...
src/mips/simulator-mips.cc:2075: if ((result & 1) != 0 && result - fs == 0.5) {
On 2012/08/24 07:21:07, ulan wrote:
> This doesn't handle the case when fs is negative, e.g. fs == -4.5, result ==
-5,
> result-fs == -0.5.

Using floor(fs + 0.5) above for negative numbers too, this expression becomes
correct:
e.g. fs = -4.5, result = -4 -> result-fs = 0.5
or fs = 4.5, result = 5 -> result-fs = 0.5
It'll be true for all other cases, because we always round half up in the first
step.

[ulan, 2012-08-27 07:23:26]

LGTM, I will land it.

https://chromiumcodereview.appspot.com/10870049/diff/1/src/mips/simulator-mip...
File src/mips/simulator-mips.cc (right):

https://chromiumcodereview.appspot.com/10870049/diff/1/src/mips/simulator-mip...
src/mips/simulator-mips.cc:2075: if ((result & 1) != 0 && result - fs == 0.5) {
On 2012/08/24 23:57:29, palfia wrote:
> On 2012/08/24 07:21:07, ulan wrote:
> > This doesn't handle the case when fs is negative, e.g. fs == -4.5, result ==
> -5,
> > result-fs == -0.5.
> 
> Using floor(fs + 0.5) above for negative numbers too, this expression becomes
> correct:
> e.g. fs = -4.5, result = -4 -> result-fs = 0.5
> or fs = 4.5, result = 5 -> result-fs = 0.5
> It'll be true for all other cases, because we always round half up in the
first
> step.

Yep, thanks for fixing it. :)