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The register width of a processor determines the range of values that can be represented in its registers. Though the vast majority of computers can perform multiple-precision arithmetic on operands in memory, allowing numbers to be arbitrarily long and overflow to be avoided, the register width limits the sizes of numbers that can be operated on (e.g., added or subtracted) using a single ...
Overflow cannot occur when the sign of two addition operands are different (or the sign of two subtraction operands are the same). [1] When binary values are interpreted as unsigned numbers, the overflow flag is meaningless and normally ignored. One of the advantages of two's complement arithmetic is that the addition and subtraction operations ...
These are most commonly manifestations of arithmetic overflow, but can also be the result of other issues. The best-known consequence of this type is the Y2K problem , but many other milestone dates or times exist that have caused or will cause problems depending on various programming deficiencies.
Arithmetic and logical instructions set some or all of the flags, and conditional jump instructions take variable action based on the value of certain flags. For example, jz (Jump if Zero), jc (Jump if Carry), and jo (Jump if Overflow) depend on specific flags. Other conditional jumps test combinations of several flags.
In the C programming language, signed integer overflow causes undefined behavior, while unsigned integer overflow causes the number to be reduced modulo a power of two, meaning that unsigned integers "wrap around" on overflow. This "wrap around" is the cause of the famous "Split Screen" in Pac-Man.
Arbitrary-precision arithmetic can also be used to avoid overflow, which is an inherent limitation of fixed-precision arithmetic. Similar to an automobile's odometer display which may change from 99999 to 00000, a fixed-precision integer may exhibit wraparound if numbers grow too large to represent at the fixed level of precision.
In C++, because dereferencing a null pointer is undefined behavior, compiler optimizations may cause other checks to be removed, leading to vulnerabilities elsewhere in the code. [29] [30] Some lists may also include race conditions (concurrent reads/writes to shared memory) as being part of memory safety (e.g., for access control).
Register (keyword), the hint in C and C++ for a variable to be placed in a register. Sethi–Ullman algorithm, an algorithm to produce the most efficient register allocation for evaluating a single expression when the number of registers required to evaluate the expression exceeds the number of available registers.