Bug 15720 – iota(long.max, long.min, step) does not work properly

Code: ------ import std.range; import std.stdio; void main() { writeln(iota(long.max, long.min, -1).length); writeln(iota(long.max, long.min, -2).length); writeln(iota(long.max, long.min, -3).length); } ------ Output: ------ 18446744073709551615 0 1 ------ Expected output: ------ 18446744073709551615 9223372036854775807 6148914691236517205 ------

This happens because the operation to compute the length is ``` unsigned((start - stop) / -step) ``` but `long.max - long.min` overflows the long and results in -1. The reason it works for a step of 1 is that -1 is cast to a ulong, which results in the maximum value of ulong (18446744073709551615). Maybe this could be fixed by casting to the unsigned type before dividing by the step.

This might be fixed with the PR written for issue 16246 as the way the end condition is checked has changed (and length calc). Once it's merged, please re-check.

Commits pushed to master at https://github.com/dlang/phobos https://github.com/dlang/phobos/commit/49ee158a9e5887ad835dc0f04c0309adf22ff965 Fix Issue 15720 - iota(long.max, long.min, step) does not work properly https://github.com/dlang/phobos/commit/138d9b91284bba8da3ceb9e5da2f52fea85db1c9 Merge pull request #5397 from andralex/15720 Fix Issue 15720 - iota(long.max, long.min, step) does not work properly merged-on-behalf-of: Vladimir Panteleev <[email protected]>

Commits pushed to stable at https://github.com/dlang/phobos https://github.com/dlang/phobos/commit/49ee158a9e5887ad835dc0f04c0309adf22ff965 Fix Issue 15720 - iota(long.max, long.min, step) does not work properly https://github.com/dlang/phobos/commit/138d9b91284bba8da3ceb9e5da2f52fea85db1c9 Merge pull request #5397 from andralex/15720

Commits pushed to dmd-cxx at https://github.com/dlang/phobos https://github.com/dlang/phobos/commit/49ee158a9e5887ad835dc0f04c0309adf22ff965 Fix Issue 15720 - iota(long.max, long.min, step) does not work properly https://github.com/dlang/phobos/commit/138d9b91284bba8da3ceb9e5da2f52fea85db1c9 Merge pull request #5397 from andralex/15720