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AIX Version 4.3 Base Operating System and Extensions Technical Reference, Volume 1

fp_cpusync Subroutine


Queries or changes the floating-point exception enable (FE) bit in the Machine Status register (MSR).

Note: This subroutine has been replaced by the fp_trapstate subroutine. The fp_cpusync subroutine is supported for compatibility, but the fp_trapstate subroutine should be used for development.


Standard C Library (libc.a)


#include <fptrap.h>
int fp_cpusync (Flag);
int Flag;


The fp_cpusync subroutine is a service routine used to query, set, or reset the Machine Status Register (MSR) floating-point exception enable (FE) bit. The MSR FE bit determines whether a processor runs in pipeline or serial mode. Floating-point traps can only be generated by the hardware when the processor is in synchronous mode.

The fp_cpusync subroutine changes only the MSR FE bit. It is a service routine for use in developing custom floating-point exception-handling software. If you are using the fp_enable or fp_enable_all subroutine or the fp_sh_trap_info or fp_sh_set_stat subroutine, you must use the fp_trap subroutine to place the process in serial mode.


Flag Specifies to query or modify the MSR FE bit:
Sets the FE bit in the MSR to Off, which disables floating-point exception processing immediately.
Sets the FE bit in the MSR to On, which enables floating-exception processing for the next floating-point operation.
Returns the current state of the process (either FP_SYNC_ON or FP_SYNC_OFF) without modifying it.

If called with any other value, the fp_cpusync subroutine returns FP_SYNC_ERROR.

Return Values

If called with the FP_SYNC_OFF or FP_SYNC_ON flag, the fp_cpusync subroutine returns a value indicating which flag was in the previous state of the process.

If called with the FP_SYNC _QUERY flag, the fp_cpusync subroutine returns a value indicating the current state of the process, either the FP_SYNC_OFF or FP_SYNC_ON flag.

Error Codes

If the fp_cpusync subroutine is called with an invalid parameter, the subroutine returns FP_SYNC_ERROR. No other errors are reported.

Related Information

The fp_any_enable, fp_is_enabled, fp_enable_all, fp_enable, fp_disable_all, or fp_disable subroutine, fp_clr_flag, fpset_flag, fp_read_flag, or fp_swap_flag subroutine, sigaction, sigvec, or signal subroutine.

Floating-Point Processor Overview in POWERstation and POWERserver Hardware Technical Information-General Architectures.

Floating-Point Exceptions Overview in AIX Version 4.3 General Programming Concepts: Writing and Debugging Programs.

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