Intel 80286 manual Glossary of 80287 and FLOATING-POINT Terminology, Glossary-3

GLOSSARY OF 80287 AND FLOATING-POINT TERMINOLOGY

Integer: a number (positive, negative, or zero) that is finite and has no fractional part. Integer can also

mean the computer representation for such a number: a sequence of data bytes, interpreted in a standard way. It is perfectly reasonable for Integers to be represented in a Floating-Point format; this is what the 80287 does whenever an Integer is pushed onto the 80287 stack.

Invalid Operation: the error condition for the 80287 that covers all cases not covered by other errors. Included are 80287 stack overflow and underflow, NaN inputs, illegal infinite inputs, out-of-range inputs, and illegal unnormal inputs.

Long Integer: an Integer format supported by the 80287 that consists of a 64-bit Two's Complement quantity.

Long Real: a Floating-Point Format supported by the 80287 that consists of a sign, an II-bit Biased Exponent, an Implicit Integer Bit, and a 52-bit Significand-a total of 64 explicit bits.

Mantissa: a term used for some non-Intel computers, meaning the Significand of a Floating-Point Number.

Masked: a term that applies to each of the six 80287 Exceptions I,D,Z,O,U,P. An exception is Masked if a corresponding bit in the 80287 Control Word is set to 1. If an exception is Masked, the 80287 will not generate an interrupt when the error condition occurs; it will instead provide its own error recovery.

NaN: an abbreviation for Not a Number; a Floating-Point quantity that does not represent any numeric or infinite quantity. NaNs should be returned by functions that encounter serious errors. If created during a sequence of calculations, they are transmitted to the final answer and can contain information about where the error occurred.

Nontrapping NaN: a NaN in which the most significant bit of the fractional part of the Significand is

1.By convention, these NaNs can undergo certain operations without visible error. Nontrapping NaNs are implemented for the 80287 via the software in EH87.LIB.

Normal: the representation of a number in a Floating-Point format in which the Significandhas an Integer bit I (either explicit or Implicit).

Normalizing Mode: a state in which nonnormal inputs are automatically converted to normal inputs whenever they are used in arithmetic. Normalizing Mode is implemented for the 80287 via the software in EH87.LIB.

NPX: Numeric Processor Extension. This is the 80287.

Overflow: an error condition in which the correct answer is finite, but has magnitude too great to be represented in the destination format.

Packed Decimal: an Integer format supported by the 80287. A Packed Decimal number is a lO-byte quantity, with nine bytes of 18 Binary Coded Decimal digits, and one byte for the sign.

Pop: to remove from a stack the last item that was placed on the stack.

Precision Control: an option, programmed through the 80287 Control Word, that allows all 80287 arithmetic to be performed with reduced precision. Because no speed advantage results from this option, its only use is for strict compatibility with the IEEE Standard, and with other computer systems.

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