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Operator | Overflow |
| Operator | Overflow |
| Operator | Overflow |
| Operator | Overflow |
|---|---|---|---|---|---|---|---|---|---|---|
yes |
| yes |
| yes |
| < | no | |||
yes |
| yes |
| yes |
| > | no | |||
yes |
| yes |
| & | no |
| >= | no | ||
yes |
| %= | no |
| | | no |
| <= | no | |
% | no |
| yes |
| ^ | no |
| == | no | |
++ | yes |
| yes |
| ~ | no |
| != | no | |
-- | yes |
| &= | no |
| ! | no |
| && | no |
= | no |
| |= | no |
| un + | no |
| || | no |
yes |
| ^= | no |
| yes |
| ?: | no |
The following sections examine specific operations that are susceptible to integer overflow. The specific tests that are required to guarantee that the operation does not result in an integer overflow depend on the signedness of the integer types. When operating on small types (smaller than int), integer conversion rules apply. The usual arithmetic conversions may also be applied to (implicitly) convert operands to equivalent types before arithmetic operations are performed. Make sure you understand implicit conversion rules before trying to implement secure arithmetic operations.
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Subtraction
Subtraction is between two operands of arithmetic type, two pointers to qualified or unqualified versions of compatible object types, or between a pointer to an object type and an integer type. (Decrementing is equivalent to subtracting one.)
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unsigned int ui1, ui2, result;
if(ui1 < ui2){
/* handle error condition */
}
result = ui1 - ui2;
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Multiplication
Multiplication is between two operands of arithmetic type.
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unsigned int ui1, ui2, result;
if( ui1 > UMAX_INT/ui2){
/* handle error condition */
}
result = ui1 * ui2;
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Division
Division is between two operands of arithmetic type. Overflow can occur during twos-complement signed integer division when the dividend is equal to the minimum (negative) value for the signed integer type and the divisor is equal to -1. Both signed and unsigned division operations are also susceptible to divide-by-zero errors.
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signed long sl1, sl2, result;
if ( (sl2 == 0) || ( (sl1 == LONG_MIN) && (sl2 == -1) ) ) {
/* handle error condition */
}
result = sl1 / sl2;
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Unary Negation
The unary negation operator takes an operand of arithmetic type. Overflow can occur during twos-complement unary negation when the operand is equal to the minimum (negative) value for the signed integer type.
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signed int si1, result;
if (si1 == INT_MIN) {
/* handle error condition */
}
result = -si1;
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Left Shift Operator
The left shift operator is between two operands of integer type.
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