Mathematical Library Functions fex_set_handling(3M)
NAME
fex_set_handling, fex_get_handling, fex_getexcepthandler,
fex_setexcepthandler - control floating point exception han-
dling modesSYNOPSIS
c99 [ flag... ] file... -lm [ library... ]
#include
int fex_set_handling(int ex, int mode, void(*handler);
int fex_get_handling(int ex);
void fex_getexcepthandler(fex_handler_t *buf, int ex);
void fex_setexcepthandler(const fex_handler_t *buf, int ex);
DESCRIPTION
These functions provide control of floating point exception handling modes. For each function, the ex argument specifiesone or more exceptions indicated by a bitwise-OR of any of
the following values defined in: FEX_INEXACT
FEX_UNDERFLOW
FEX_OVERFLOW
FEX_DIVBYZERO division by zero
FEX_INV_ZDZ 0/0 invalid operation
FEX_INV_IDI infinity/infinity invalid operation
FEX_INV_ISI infinity-infinity invalid operation
FEX_INV_ZMI 0*infinity invalid operation
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Mathematical Library Functions fex_set_handling(3M)
FEX_INV_SQRT square root of negative operand
FEX_INV_SNAN signaling NaN
FEX_INV_INT invalid integer conversion
FEX_INV_CMP invalid comparison
For convenience, the following combinations of values are also defined:FEX_NONE no exceptions
FEX_INVALID all invalid operation exceptions
FEX_COMMON overflow, division by zero, and invalid
operationFEX_ALL all exceptions
The fex_set_handling() function establishes the specified
mode for handling the floating point exceptions identified by ex. The selected mode determines the action to be taken when one of the indicated exceptions occurs. It must be one of the following values:FEX_NOHANDLER Trap but do not otherwise handle the excep-
tion, evoking instead whatever ambient behavior would normally be in effect. This is the default behavior when the exception's trap is enabled. The handler parameter is ignored.FEX_NONSTOP Provide the IEEE 754 default result for the
operation that caused the exception, setthe exception's flag, and continue execu-
tion. This is the default behavior when the exception's trap is disabled. The handler parameter is ignored.SunOS 5.11 Last change: 12 Jul 2006 2
Mathematical Library Functions fex_set_handling(3M)
FEX_ABORT Call abort(3C). The handler parameter is
ignored.FEX_SIGNAL Invoke the function *handler with the
parameters normally supplied to a signal handler installed with sigfpe(3C).FEX_CUSTOM Invoke the function *handler as described
in the next paragraph.In FEX_CUSTOM mode, when a floating point exception occurs,
the handler function is invoked as though its prototype were:#include
void handler(int ex, fex_info_t *info);
On entry, ex is the value (of the first twelve listed above)corresponding to the exception that occurred, info->op indi-
cates the operation that caused the exception, info->op1 and
info->op2 contain the values of the operands, info->res con-
tains the default untrapped result value, and info->flags
reflects the exception flags that the operation would have set had it not been trapped. If the handler returns, thevalue contained in info->res on exit is substituted for the
result of the operation, the flags indicated by info->flags
are set, and execution resumes at the point where the excep-
tion occurred. The handler might modify info->res and
info->flags to supply any desired result value and flags.
Alternatively, if the exception is underflow or overflow, the hander might setinfo->res.type = fex_nodata;
which causes the exponent-adjusted result specified by IEEE
754 to be substituted. If the handler does not modifyinfo->res or info->flags, the effect is the same as if the
exception had not been trapped. Although the default untrapped result of an exceptionaloperation is always available to a FEX_CUSTOM handler, in
some cases, one or both operands may not be. In thesecases, the handler may be invoked with info->op1.type ==
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Mathematical Library Functions fex_set_handling(3M)
fex_nodata or info->op2.type == fex_nodata to indicate that
the respective data structures do not contain valid data.(For example, info->op2.type == fex_nodata if the excep-
tional operation is a unary operation.) Before accessing the operand values, a custom handler should always examine the type field of the operand data structures to ensure that they contain valid data in the appropriate format.The fex_get_handling() function returns the current handling
mode for the exception specified by ex, which must be one of the first twelve exceptions listed above.The fex_getexcepthandler() function saves the current han-
dling modes and associated data for the exceptions specified by ex in the data structure pointed to by buf. The typefex_handler_t is defined in
. The fex_setexcepthandler() function restores the handling
modes and associated data for the exceptions specified by exfrom the data structure pointed to by buf. This data struc-
ture must have been set by a previous call tofex_getexcepthandler(). Otherwise the effect on the indi-
cated modes is undefined.RETURN VALUES
The fex_set_handling() function returns a non-zero value if
the requested exception handling mode is established. Other-
wise, it returns 0.EXAMPLES
The following example demonstrates how to substitute apredetermined value for the result of a 0/0 invalid opera-
tion.#include
#include
double k;void presub(int ex, fex_info_t *info) {
info->res.type = fex_double;
info->res.val.d = k;
} int main() { double x, w; int i;fex_handler_t buf;
/*SunOS 5.11 Last change: 12 Jul 2006 4
Mathematical Library Functions fex_set_handling(3M)
* save current 0/0 handler */(void) fex_getexcepthandler(&buf, FEX_INV_ZDZ);
/* * set up presubstitution handler for 0/0 */(void) fex_set_handling(FEX_INV_ZDZ, FEX_CUSTOM, presub);
/* * compute (k*x)/sin(x) for k=2.0, x=0.5, 0.4, ..., 0.1, 0.0 */ k = 2.0; (void) printf("Evaluating f(x) = (k*x)/sin(x)\n\n");for (i = 5; i >= 0; i--) {
x = (double) i * 0.1; w = (k * x) / sin(x);(void) printf("\tx=%3.3f\t f(x) = % 1.20e\n", x, w);
} /* * restore old 0/0 handler */(void) fex_setexcepthandler(&buf, FEX_INV_ZDZ);
return 0; } The output from the preceding program reads: Evaluating f(x) = (k*x)/sin(x) x=0.500 f(x) = 2.08582964293348816000e+00 x=0.400 f(x) = 2.05434596443822626000e+00 x=0.300 f(x) = 2.03031801709447368000e+00 x=0.200 f(x) = 2.01339581906893761000e+00 x=0.100 f(x) = 2.00333722632695554000e+00 x=0.000 f(x) = 2.00000000000000000000e+00 When x = 0, f(x) is computed as 0/0 and an invalid operationexception occurs. In this example, the value 2.0 is substi-
tuted for the result.ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:SunOS 5.11 Last change: 12 Jul 2006 5
Mathematical Library Functions fex_set_handling(3M)
_____________________________________________________________
| ATTRIBUTE TYPE ATTRIBUTE VALUE |
| Availability system/library/math, SUNWlmxs| | Interface Stability Committed || MT-Level MT-Safe (see Notes) |
|____________________________________________________________|
SEE ALSO
sigfpe(3C), feclearexcept(3M), fegetenv(3M),fex_set_log(3M), attributes(5)
Numerical Computation Guide NOTES In a multithreaded application, the preceding functions affect exception handling modes only for the calling thread. The functions described on this page automatically install and deinstall SIGFPE handlers and set and clear the trap enable mode bits in the floating point status register as needed. If a program uses these functions and attempts to install a SIGFPE handler or control the trap enable mode bits independently, the resulting behavior is not defined. All traps are disabled before a handler installed inFEX_CUSTOM mode is invoked. When the SIGFPE signal is
blocked, as it is when such a handler is invoked, the float-
ing point environment, exception flags, and retrospective diagnostic functions described in feclearexcept(3M),fegetenv(3M), and fex_set_log(3M) do not re-enable traps.
Thus, the handler itself always runs in FEX_NONSTOP mode
with logging of retrospective diagnostics disabled. Attempting to change these modes within the handler may not produce the expected results.SunOS 5.11 Last change: 12 Jul 2006 6