P.times() carry problem

[jsyt]

big.js line 848

c[j] = (c[j] + b) % 10;

If there is a carry here, then you have not processed the carry.

If there is no carry I think the following is better.

c[j] =  b;

I don't think there will be a carry in here.

So if I replace c[j] = (c[j] + b) % 10; with c[j] = b;, will there be any problem here?

Thank you!

[MikeMcl]

I don't think there will be a carry in here.

b is the carry, so I do not know what you mean here, or in the other sentences in which you have used the word "carry".

Without meticulously studying this time-tested algorithm I wrote years ago, I cannot be sure if it is safe to replace c[j] = (c[j] + b) % 10; with just c[j] = b;. There may be edge cases not included in the tests that mean it cannot be.

Will c[j] will always be zero at that point and will b always be equal to b % 10?

[jsyt]

b is the carry, so I do not know what you mean here, or in the other sentences in which you have used the word "carry".

I mean that if c[j] != 0, then(c[j] + b) may get a carry, and you have not processed the carry.

Will c[j] will always be zero at that point and will b always be equal to b % 10?

Yes, I think that c[j] will always be zero at that point and b always be equal to b % 10.

Thank you!

[MikeMcl]

You just "think" or are you absolutely 100% sure? Unfortunately, I am not able to study this closely at the moment.

[jsyt]

You just "think" or are you absolutely 100% sure? Unfortunately, I am not able to study this closely at the moment.

I am absolutely 100% sure that c[j] will always be zero at that point and b always be equal to b % 10.
And I replace c[j] = (c[j] + b) % 10; with c[j] = b;, it passed all the test cases.

[MikeMcl]

Okay, I will accept a pull request with this change, if you so wish.

I sure hope you know what you are doing.

[dkent600]

Seems like would be good to include a test case that goes from red to green by this.

[MikeMcl]

@dkent600

This wasn't a bug, just a minor optimisation.

BTW I was speaking tongue-in-cheek when I wrote "I sure hope you know what you are doing" above.