I will discuss the
100000000000000000000000.0000000000000000000000000000000000000000000001
issue
with the V8 team on monday.
The way I see it we have two options:
1. Follow ECMA-262 and round down, thus being incompatible with older
versions.
2. Fallback to a more expensive reading when there are more than 20 digits.
Pros/Cons for 1:
Pro: Basically nothing to do. That's what we have now.
Cons: Incompatible and we might numbers the "wrong" way. On the other hand
these
numbers have to be written by hand (toString/toExponential/toFixed will
never
produce a number that would make such problems). Therefore they are
extremely
rare.
Pros/Cons for 2:
Pro: Compatible with older variants of V8. Reading is correct. Might
slightly
simplify the fast case: the exponent would need to be in range -999 to 999.
Cons: we would need to keep/add a fallback method. Maybe a template taking
either a fixed-size buffer or a dynamic vector would do the trick, though.
http://codereview.chromium.org/1096002/diff/3002/4003
File src/conversions.cc (right):
http://codereview.chromium.org/1096002/diff/3002/4003#newcode109
src/conversions.cc:109: bool operator != (EndMarker const& m) const {
return !(*this == m); }
On 2010/03/19 15:46:12, SeRya wrote:
On 2010/03/18 20:34:22, Erik Corry wrote:
> Some funky C++ here :-). return !end_; seems simpler, but perhaps
this is
> somehow better?
Just a canonical form of != which simplifies maintenance (IMHO).
I'm with Erik here.
I still don't understand how this actually types. (Although I'm by no
means a C++ expert).
Also operator-overloading should be rare in Google code.
Why not Peek(), AtEnd(), etc?
This said, I'm not very familiar with V8 coding practices.
http://codereview.chromium.org/1096002/diff/3002/4003#newcode496
src/conversions.cc:496: const int max_exponent = INT_MAX / 2;
On 2010/03/19 15:46:12, SeRya wrote:
On 2010/03/19 13:39:43, Florian Loitsch wrote:
> This seems to be too complicated. A decimal number without leading
0s may only
> have a decimal exponent of ~-400 to ~+400 before ending up being
infinite or
0.
1<1000 zeros>e-1000 == 1.
Right you are.
http://codereview.chromium.org/1096002/diff/3002/4003#newcode519
src/conversions.cc:519: if (exponent != 0) {
On 2010/03/19 15:46:12, SeRya wrote:
On 2010/03/19 13:39:43, Florian Loitsch wrote:
> not that it really matters, but you could copy the exponent
characters while
> reading them, and just stop after 4 digits.
> This way you could avoid this part here.
It would mean another chunk of code that which drop leading zeros and
check for
junk tail. I'd prefer to simplify for now and may be add this
optimization
later.
my comment was based on the assumption that the read exponent was in
range -400 to +400. So disregard it.
http://codereview.chromium.org/1096002/diff/21004/27003#newcode298
src/conversions.cc:298: // 1. currnet == end (other ops are not
allowed), current != end.
Are we sure there is at least one character?
If yes assert it.
If not, and it is legal to access current[0] of empty string, explain.
http://codereview.chromium.org/1096002/diff/21004/27003#newcode330
src/conversions.cc:330: buffer[buffer_pos++] = '-';
It might make sense to move the hexadecimal reading into a separate
function.
http://codereview.chromium.org/1096002/diff/21004/27003#newcode405
src/conversions.cc:405: if (current == end) return signed_zero;
I think it makes more sense to structure as follows:
if (current == end) {
if (significant_digits == 0 && !leading_zero) {
// String was ".".
return JUNK_STRING_VALUE;
} else {
goto parsing_done;
}
}
if (significant_digits == 0) {
octal = false;
...
}
http://codereview.chromium.org/1096002/diff/21004/27003#newcode451
src/conversions.cc:451: }
How should "123e" be parsed when "trailing junk is enabled?
as "123" or as JUNK_STRING_VALUE?
If it's the latter, then this is fine.
http://codereview.chromium.org/1096002/diff/21004/27003#newcode456
src/conversions.cc:456: ++current;
As before: should 123e+ be parsed as 123 or JUNK_STRING_VALUE when
trailing junk is enabled.
http://codereview.chromium.org/1096002
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