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version 2.109.1

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Function core.checkedint.addu

Add two unsigned integers, checking for overflow (aka carry).

uint addu (
  uint x,
  uint y,
  ref bool overflow
);

ulong addu (
  ulong x,
  ulong y,
  ref bool overflow
);

The overflow is sticky, meaning a sequence of operations can be done and overflow need only be checked at the end.

Parameters

NameDescription
x left operand
y right operand
overflow set if an overflow occurs, is not affected otherwise

Returns

the sum

Example

for (uint i = 0; i < 10; ++i)
{
    bool overflow;
    immutable uint r = addu (uint.max - i, uint.max - i, overflow);
    writeln(r); // 2 * (uint.max - i)
    assert (overflow);
}

bool overflow;
writeln(addu(2, 3, overflow)); // 5
assert(!overflow);

writeln(addu(1, uint.max - 1, overflow)); // uint.max
assert(!overflow);

writeln(addu(uint.min, -1, overflow)); // uint.max
assert(!overflow);

writeln(addu(uint.max, 1, overflow)); // uint.min
assert(overflow);

overflow = false;
writeln(addu(uint.min + 1, -1, overflow)); // uint.min
assert(overflow);

writeln(addu(0, 0, overflow)); // 0
assert(overflow);                   // sticky

Example

bool overflow;
writeln(addu(2L, 3L, overflow)); // 5
assert(!overflow);

writeln(addu(1, ulong.max - 1, overflow)); // ulong.max
assert(!overflow);

writeln(addu(ulong.min, -1L, overflow)); // ulong.max
assert(!overflow);

writeln(addu(ulong.max, 1, overflow)); // ulong.min
assert(overflow);

overflow = false;
writeln(addu(ulong.min + 1, -1L, overflow)); // ulong.min
assert(overflow);

writeln(addu(0L, 0L, overflow)); // 0
assert(overflow);                   // sticky

Authors

Walter Bright

License

Boost License 1.0