ext/bcmath: Supports scientific notation

[SakiTakamachi]

related #17876

This probably requires an RFC, or at least a discussion on the mailing list, so I'll send an email once I've polished the code a bit more.

This change is to support code like this:

var_dump(
    new BcMath\Number('1.23e1'),
    new BcMath\Number('4.567E4'),
    new BcMath\Number('8.9e-2'),
    new BcMath\Number('1.2345E-5'),
);

output:

object(BcMath\Number)#1 (2) {
  ["value"]=>
  string(4) "12.3"
  ["scale"]=>
  int(1)
}
object(BcMath\Number)#2 (2) {
  ["value"]=>
  string(5) "45670"
  ["scale"]=>
  int(0)
}
object(BcMath\Number)#3 (2) {
  ["value"]=>
  string(5) "0.089"
  ["scale"]=>
  int(3)
}
object(BcMath\Number)#4 (2) {
  ["value"]=>
  string(11) "0.000012345"
  ["scale"]=>
  int(9)
}

I've used the Number class as an easy example to follow, but functions will accept these values ​​as well.

Benchmark

This change will make it a bit slower, but that may be tolerable.
(This is just a prototype, so there is a possibility that it could be improved further.)

The performance seems to be about the same.

code:

for ($i = 0; $i < 4000000; $i++) {
    $num = new BcMath\Number('1.2345678901234567890');
}

result (first commit):

Benchmark 1: /php-dev/sapi/cli/php /mount/bc/num/1.php
  Time (mean ± σ):     352.8 ms ±   1.7 ms    [User: 342.4 ms, System: 5.1 ms]
  Range (min … max):   349.6 ms … 354.9 ms    10 runs
 
Benchmark 2: /master/sapi/cli/php /mount/bc/num/1.php
  Time (mean ± σ):     345.0 ms ±   4.2 ms    [User: 334.1 ms, System: 5.3 ms]
  Range (min … max):   341.8 ms … 352.7 ms    10 runs
 
Summary
  '/master/sapi/cli/php /mount/bc/num/1.php' ran
    1.02 ± 0.01 times faster than '/php-dev/sapi/cli/php /mount/bc/num/1.php'

result (after commit 4)

Benchmark 1: /php-dev/sapi/cli/php /mount/bc/num/1.php
  Time (mean ± σ):     343.0 ms ±   2.6 ms    [User: 331.3 ms, System: 6.2 ms]
  Range (min … max):   339.8 ms … 347.7 ms    10 runs
 
Benchmark 2: /master/sapi/cli/php /mount/bc/num/1.php
  Time (mean ± σ):     344.5 ms ±   5.6 ms    [User: 333.9 ms, System: 5.3 ms]
  Range (min … max):   338.9 ms … 357.0 ms    10 runs
 
Summary
  '/php-dev/sapi/cli/php /mount/bc/num/1.php' ran
    1.00 ± 0.02 times faster than '/master/sapi/cli/php /mount/bc/num/1.php'

[nielsdos]

This is false, e.g. 12e-3 should evaluate to 0.012.

[SakiTakamachi]

@nielsdos

I remember that this is what the ISO says, but I may be remembering it wrong...

I'll fix it

[SakiTakamachi]

ditto