Suggest better ways to deal with division

[hearty wharf]

https://github.com/AntonC9018/thesis-png/blob/94ab6d83e05f169970f4936efe39f56d4c0cd839/src/main.zig#L73-L90
Is there some more clean way of using the special division instructions to remove these casts? And maybe even the check if it's less than zero?

I kinda looked at those in the docs, but in the end just settled with the casts, because they are more familiar, and I just can't imagine how to do this properly with the div instructions.

Ah actually that code has got a bug in it after all

[hearty wharf]

https://github.com/AntonC9018/thesis-png/blob/92c51b0b62fce844a7906ea67960046ea347c5eb/src/main.zig#L73

The bug fixed

[hybrid shard]

.byte = self.byte + @divFloor(self.bit, bitsInByte)
.bit = @mod(self.bit, bitsInByte)

sounds like you want this

[hearty wharf]

floor rounds to negatives, doesn't it?

[hybrid shard]

floor rounds to negative infinity, yes

[hearty wharf]

Yeah, seems to be working

Thanks

So if it's negative, the division will always give me -1, minus what the positive division would give

[hybrid shard]

not necessarily

it gives you the most negative quotient

[hearty wharf]

I can't visualize that

[hybrid shard]

-8 / 8 = -1, -1 / 8 = -1, -9 / 8 = -2

the identity that matters here is (@divFloor(a, b) * b) + @mod(a, b) == a

[hearty wharf]

So that is an identity

I've seen that in the doc

But it's not clear that is an identity

It's given as example code

[hybrid shard]

it is example code

it's an example showing that a certain identity is true, a and b can be any value

[hearty wharf]

Well I'm saying that's not clear at all

It doesn't say that's a fact

and it doesn't say what a and b can be

... -- this is true for any valid a and b