Floating point exceptions and the ieee standard 754

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Unformatted text preview: se to NaN operands is also included in more detail than in Section, "NaNs." For floating-point exception priority, refer to "Priority Among Simultaneous Exceptions and Interrupts" in Chapter 5, E-6 Vol. 1 GUIDELINES FOR WRITING SIMD FLOATING-POINT EXCEPTION HANDLERS "Interrupt and Exception Handling," of Intel 64 and IA-32 Architectures Software Developer's Manual, Volume 3A. E.4.2.1 Numeric Exceptions There are six classes of numeric (floating-point) exception conditions that can occur: Invalid operation (#I), Divide-by-Zero (#Z), Denormal Operand (#D), Numeric Overflow (#O), Numeric Underflow (#U), and Inexact Result (precision) (#P). #I, #Z, #D are pre-computation exceptions (floating-point faults), detected before the arithmetic operation. #O, #U, #P are post-computation exceptions (floating-point traps). Users can control how the SSE/SSE2/SSE3 floating-point exceptions are handled by setting the mask/unmask bits in MXCSR. Masked exceptions are handled by the processor, or by software if they are combined with unmasked exceptions occurring in the same instruction. Unmasked exceptions are usually handled by the low-level exception handler, in conjunction with user-level software. E.4.2.2 Results of Operations with NaN Operands or a NaN Result for SSE/SSE2/SSE3 Numeric Instructions The tables below (E-1 through E-10) specify the response of SSE/SSE2/SSE3 instructions to NaN inputs, or to other inputs that lead to NaN results. These results will be referenced by subsequent tables (e.g., E-10). Most operations do not raise an invalid exception for quiet NaN operands, but even so, they will have higher precedence over raising floating-point exceptions other than invalid operation. Note that the single precision QNaN Indefinite value is 0xffc00000, the double precision QNaN Indefinite value is 0xfff8000000000000, and the Integer Indefinite value is 0x80000000 (not a floating-point number, but it can be the result of a conversion instruction from floating-point to integer). For an unmasked exception, no result will be provided by the hardware to the user handler. If a user registered floating-point exception handler is invoked, it may provide a result for the excepting instruction, that will be used if execution of the application code is continued after returning from the interruption. In Tables E-1 through Table E-12, the specified operands cause an invalid exception, unless the unmasked result is marked with "not an exception". In this latter case, the unmasked and masked results are the same. Vol. 1 E-7 GUIDELINES FOR WRITING SIMD FLOATING-POINT EXCEPTION HANDLERS Table E-1. ADDPS, ADDSS, SUBPS, SUBSS, MULPS, MULSS, DIVPS, DIVSS, ADDPD, ADDSD, SUBPD, SUBSD, MULPD, MULSD, DIVPD, DIVSD, ADDSUBPS, ADDSUBPD, HADDPS, HADDPD, HSUBPS, HSUBPD Source Operands SNaN1 op SNaN2 1 Masked Result SNaN1 | 00400000H or SNaN1 | 0008000000000000H2 SNaN1 | 00400000H or SNaN1 | 0008000000000000H2 QNaN1 QNaN1 SNaN | 0040000...
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