The default action for this signal is to terminate the program. See Signal Handling , for how you can change the effect of the signal. This exception is raised if the given operands are invalid for the operation to be performed.
Examples are see IEEE , section 7 :. The stack trace recorded with a retrospective diagnostic message contains only instruction addresses and function names; for additional debugging information such as line numbers, source file names, and argument values, you must use a debugger. The log of retrospective diagnostics does not contain information about every single exception that occurs; if it did, a typical log would be huge, and it would be impossible to isolate unusual exceptions. Instead, the logging mechanism eliminates redundant messages.
A message is considered redundant under either of two circumstances:. In particular, in most programs, only the first occurrence of each type of exception will be logged. The following example combines logging of retrospective diagnostics with the shared object preloading facility illustrated in the previous section. The preceding output shows that the invalid operation exception was raised as a result of a square root operation in the routine sqrtm1.
Appendix A gives more examples showing typical log outputs. Historically, most numerical software has been written without regard to exceptions for a variety of reasons , and many programmers have become accustomed to environments in which exceptions cause a program to abort immediately.
Now, some high-quality software packages such as LAPACK are being carefully designed to avoid exceptions such as division by zero and invalid operations and to scale their inputs aggressively to preclude overflow and potentially harmful underflow. Neither of these approaches to dealing with exceptions is appropriate in every situation.
However, ignoring exceptions can pose problems when one person writes a program or subroutine that is intended to be used by someone else perhaps someone who does not have access to the source code , and attempting to avoid all exceptions can require many defensive tests and branches and carry a significant cost see Demmel and Li, "Faster Numerical Algorithms via Exception Handling," IEEE Trans.
The default exception response, status flags, and optional trapping facility of IEEE arithmetic are intended to provide a third alternative: continuing a computation in the presence of exceptions and either detecting them after the fact or intercepting and handling them as they occur. In order to continue the computation, however, the IEEE standard recommends that a trap handler be able to provide a result for the operation that incurred an exception.
When a SIGFPE signal handler is invoked as a result of a trapped floating point exception, the uap parameter points to a data structure that contains a copy of the machine's integer and floating point registers as well as other system-dependent information describing the exception. If the signal handler returns normally, the saved data are restored and the program resumes execution at the point at which the trap was taken.
Thus, by accessing and decoding the information in the data structure that describes the exception and possibly modifying the saved data, a SIGFPE handler can substitute a user-supplied value for the result of an exceptional operation and continue computation. Specifically, this structure contains a code representing the arithmetic operation that caused the exception and structures recording the operands, if they are available. It also contains a structure recording the default result that would have been substituted if the exception were not trapped and an integer value holding the bitwise "or" of the exception flags that would have accrued.
The handler can modify the latter members of the structure to substitute a different result or change the set of flags that are accrued. Note that if the handler returns without modifying these data, the program will continue with the default untrapped result and flags just as if the exception were not trapped. As an illustration, the following section shows how to substitute a scaled result for an operation that underflows or overflows.
See Appendix A for further examples. The IEEE standard recommends that when underflow and overflow are trapped, the system should provide a way for a trap handler to substitute an exponent-wrapped result, i. The scale factor is chosen to map underflowed and overflowed results as nearly as possible to the middle of the exponent range so that subsequent computations will be less likely to underflow or overflow further. By keeping track of the number of underflows and overflows that occur, a program can scale the final result to compensate for the exponent wrapping.
See P. Sterbenz, Floating-Point Computation. On SPARC, when a floating point instruction incurs a trapped exception, the system leaves the destination register unchanged. The following example shows a handler that performs these steps. In typical usage, the volatile declarations would not be needed. The output from the preceding program is: On x86, the floating point hardware provides the exponent-wrapped result when a floating point instruction incurs a trapped underflow or overflow and its destination is a register.
When trapped underflow or overflow occurs on a floating point store instruction, however, the hardware traps without completing the store and without popping the stack, if the store instruction is a store-and-pop. The following example illustrates such a handler. On SPARC systems, the information supplied to such a handler always includes the operation that caused the exception and the operands, and this information is sufficient to allow the handler to compute the IEEE exponent-wrapped result, as shown above.
See the fenv. Moreover, the x86 hardware delivers an exponent-wrapped result automatically, and this can overwrite one of the operands if the destination of the excepting instruction is a floating point register.
When either of these exceptions is trapped, the handler can set. The output from the preceding program resembles the following: Floating point overflow at 0x main, handler: handler 0x main Chapter 4. Predicates Invalid Exception. Value Exception. Numerical Computation Guide. The following table provides a starting point for some common operating systems:. In this noncompliant code example, floating-point operations are performed without checking for errors. Note that range checking has been intentionally omitted because the intent is to detect errors following the floating-point operation.
However, exceptional conditions as indicated by the comments occur that may lead to unexpected arithmetic results. Microsoft Visual Studio and earlier versions do not support C functions to handle floating-point errors. Microsoft Visual Studio also uses structured exception handling SEH to handle floating-point operations.
SEH provides more information about the error and allows the programmer to change the results of the floating-point operation that caused the error condition. Undetected floating-point errors may result in lower program efficiency, inaccurate results, or software vulnerabilities. Most processors stall for a significant duration when an operation incurs a NaN not a number value. Could detect violations of this rule by ensuring that floating-point operations are surrounded by feclearexcept and fetestexcept.
It would need to look for type conversions to float or double, divisions by a number not known to be nonzero , and multiplication. It may be wisest to apply this to all floating-point operations in general. Avoid division by zero Avoid implicit conversions from wider to narrower floating type Avoid implicit conversions from narrower to wider floating type Avoid implicit conversions of floating point numbers from wider to narrower floating type.
Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Ask Question. Asked 10 years, 11 months ago. Active 1 year, 8 months ago. Viewed k times. Improve this question. Ian Kemp Something is wrong with your for loop.
Add a comment. Active Oldest Votes. Improve this answer. Crashworks Crashworks Okay, well let me make sure I understand my own code before I try to fix it. Yes, thats the entire reason for a for loop. The loop runs, then it does something in your case i-- then it runs the loop again until the condition at the top is no longer true.
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