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version 2.106.0

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Function core.checkedint.subu

Subtract two unsigned integers, checking for overflow (aka borrow).

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

ulong subu (
  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 difference

Example

bool overflow;
writeln(subu(3, 2, overflow)); // 1
assert(!overflow);

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

writeln(subu(1, 1, overflow)); // uint.min
assert(!overflow);

writeln(subu(0, 1, overflow)); // uint.max
assert(overflow);

overflow = false;
writeln(subu(uint.max - 1, uint.max, overflow)); // uint.max
assert(overflow);

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

Example

bool overflow;
writeln(subu(3UL, 2UL, overflow)); // 1
assert(!overflow);

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

writeln(subu(1UL, 1UL, overflow)); // ulong.min
assert(!overflow);

writeln(subu(0UL, 1UL, overflow)); // ulong.max
assert(overflow);

overflow = false;
writeln(subu(ulong.max - 1, ulong.max, overflow)); // ulong.max
assert(overflow);

writeln(subu(0UL, 0UL, overflow)); // 0
assert(overflow);                   // sticky

Authors

Walter Bright

License

Boost License 1.0