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Unformatted text preview: d and Unmasked Exceptions In situations where both masked and unmasked exceptions are detected, the processor will set exception flags for the masked and the unmasked exceptions. However, it will not return masked results until after the processor has detected and handled unmasked post-computation exceptions and returned from the exception handler (as in step 6 above) to finish executing the instruction. 11.5.4 Handling SIMD Floating-Point Exceptions in Software Section 4.9.3, "Typical Actions of a Floating-Point Exception Handler," shows actions that may be carried out by a SIMD floating-point exception handler. The SSE/SSE2/SSE3 state is saved with the FXSAVE instruction (see Section 11.6.5, "Saving and Restoring the SSE/SSE2 State"). 11.5.5 Interaction of SIMD and x87 FPU Floating-Point Exceptions SIMD floating-point exceptions are generated independently from x87 FPU floatingpoint exceptions. SIMD floating-point exceptions do not cause assertion of the FERR# pin (independent of the value of CR0.NE[bit 5]). They ignore the assertion and deassertion of the IGNNE# pin. If applications use SSE/SSE2/SSE3 instructions along with x87 FPU instructions (in the same task or program), consider the following: SIMD floating-point exceptions are reported independently from the x87 FPU floating-point exceptions. SIMD and x87 FPU floating-point exceptions can be unmasked independently. Separate x87 FPU and SIMD floating-point exception handlers must be provided if the same exception is unmasked for x87 FPU and for SSE/SSE2/SSE3 operations. The rounding mode specified in the MXCSR register does not affect x87 FPU instructions. Likewise, the rounding mode specified in the x87 FPU control word does not affect the SSE/SSE2/SSE3 instructions. To use the same rounding mode, the rounding control bits in the MXCSR register and in the x87 FPU control word must be set explicitly to the same value. The flush-to-zero mode set in the MXCSR register for SSE/SSE2/SSE3 instructions has no counterpart in the x87 FPU. For compatibility with the x87 FPU, set the flush-to-zero bit to 0. The denormals-are-zeros mode set in the MXCSR register for SSE/SSE2/SSE3 instructions has no counterpart in the x87 FPU. For compatibility with the x87 FPU, set the denormals-are-zeros bit to 0. 11-26 Vol. 1 PROGRAMMING WITH STREAMING SIMD EXTENSIONS 2 (SSE2) An application that expects to detect x87 FPU exceptions that occur during the execution of x87 FPU instructions will not be notified if exceptions occurs during the execution of corresponding SSE/SSE2/SSE31 instructions, unless the exception masks that are enabled in the x87 FPU control word have also been enabled in the MXCSR register and the application is capable of handling SIMD floating-point exceptions (#XF). -- Masked exceptions that occur during an SSE/SSE2/SSE3 library call cannot be detected by unmasking the exceptions after the call (in an attempt to generate the fault based on the fact that an exception flag...
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