why $ is need to access array [negative index]?
clap at trap.com
Sun Sep 20 14:01:58 UTC 2020
On Friday, 18 September 2020 at 21:31:53 UTC, IGotD- wrote:
> On Friday, 18 September 2020 at 20:46:00 UTC, mw wrote:
>> Currently we have range check on every single indexing
>> operation already; so the trade-off here is: adding one more
>> check v.s. the convenience it buys.
> We want as few range checks as possible because indexing arrays
> are not too seldom done it loops. Adding an extra check could
> affect performance in this case.
You dont need an extra check, you just do an unsigned comparison,
negative values will interpreted as larger. IE...
int idx = length-i;
assert(cast(unsigned) idx < length)
catches anything outside the valid range.
Yes you have the issue that the index could wrap around and end
up valid, but you already have that anyway. I mean if (idx-1) is
going to cause a problem so will (idx+0xFFFFFFFF)
More information about the Digitalmars-d