https://issues.dlang.org/show_bug.cgi?id=13231
Issue ID: 13231
Summary: Safe left shift for checkedint
Product: D
Version: D2
Hardware: x86
OS: Windows
Status: NEW
Severity: enhancement
Priority: P1
Component: druntime
Assignee: [email protected]
Reporter: [email protected]
The purpose of checkedint functions/intrinsics is to detect overflows and bugs.
When you have a number x of type int/uint/long/ulong where one or more of the
most n significant bits is set to 1, and you shift x on left by n, you lose
some information, so you have an overflow.
So I suggest to add to the checkedint.d module the leftShift functions that
perform a checked left shifting. They should also warn against too much large
shifts:
leftShift(in uint x, in uint n, ref bool overflow)
leftShift(in ulong x, in uint n, ref bool overflow)
They check that:
1) n is in the appropriate range [0, sizeof(x) * 8]. Otherwise they set
overflow to true.
2) None of the n most significant bits of x is 1 before the shifting.
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