Can Integer Division by Zero Trigger a Floating-Point Exception?

Integer Division by Zero and Floating Point Exceptions

In another discussion, a user encountered a "floating point error" in their C code despite integer divide-by-zero being the actual issue. This prompted a debate on whether floating point exceptions can arise from integer divide-by-zero operations.

Traditionally, integer divide-by-zero has been viewed as generating an integer exception (#DE on IA-32 and AMD64), while floating-point divide-by-zero triggers a floating-point exception (interrupt 16 or 19). However, some platforms deviate from this convention.

POSIX and Integer Division

According to the POSIX standard, a divide-by-zero operation on integer operands must generate the SIGFPE signal, an indication of a floating point exception. This means that on POSIX systems, integer division by zero will be reported as a floating point exception.

GNU/Linux and SIGFPE

For many Linux systems using the GNU C Library (glibc), SIGFPE provides additional information through the siginfo_t object's si_code field. For integer divide-by-zero, the value of this field will be FPE_INTDIV_TRAP.

Windows and Integer Division

Information is not readily available on how Windows handles integer divide-by-zero exceptions. It is possible that Windows uses a distinct exception type or packages different arithmetic exceptions into a single category similar to Unix.

IEEE754 Divide-by-Zero Semantics

In contrast to integer arithmetic, the IEEE754 floating-point standard defines specific behavior for divide-by-zero operations:

• 0.0/0.0 results in NaN (not-a-number)
• Finite x / 0.0 results in /-Inf (infinity) with the sign of x

Masking and Detection of Floating Point Exceptions

In most operating systems and C ABIs, floating point exceptions are masked by default for user-space processes. This allows for the propagation of error values (NaN and Inf) through calculations without causing a trap.

Integer Overflow and Sticky Flags

Proposals have been made for "sticky" integer-overflow flags to record overflows during computation sequences. However, integer overflow detection methods vary across architectures, with x86 requiring conditional branches after each calculation and MIPS providing specific instructions for trapping on signed overflow.

Conclusion

The behavior of integer divide-by-zero and the handling of floating point exceptions vary across platforms. While some systems (such as POSIX systems) treat integer divide-by-zero as a floating point exception, others may distinguish them. It is important to be aware of the specific error reporting mechanisms on the target platform when debugging such issues.

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