DRAFT IEEE Standard for Binary Floating-Point Arithmetic - Sonic.net

DRAFT IEEE Standard for Floating-Point Arithmetic – 2003 August 12 10:20
Rationale: I am not sure if I have ever used case (class(..., when I was concerned about performance; in
that case I typically use a sequence like isnormal – finite – iszero; isinf, issignaling, in order to get to the
common case first.
Simple one-operand logical predicates have a higher chance of hardware implementation, programmer
usage in performance-oriented code, and correct compiler optimization.
Classification predicates (Section 5.9) and functions (Appendix A) are much more efficient if hardware
implementations of floating-point registers classify their contents as they are loaded or computed, and
record the classification into extra tag bits for each register.
§BI Standardize quiet functions.
Rationale: these functions are usually implemented without exceptions.
§FMA Fused multiply-add.
Rationale: Standardize a best practice for fused multiply-add operations, which are now available in
several instruction sets, often implemented slightly differently. Note that 0 × ∞ + qnan does not signal
invalid, because a NaN is an operand, but 0 × ∞ + ∞ does signal invalid, and generates qnan rather
than ∞, because no operand is NaN, and even if all three operands have positive sign bits, the product
is still undefined. In general, an operation with a floating-point destination can generate an invalid
exception if no operand is a quiet NaN, and generates no invalid exception if one or more operands is a
quiet NaN and none is a signaling NaN.
12 November 2001
§Q Quad: Add 128-bit quadruple precision with 112 fraction bits and implicit integer bit. Rationale:
match existing hardware and software implementations, and discourage undesirable alternatives such as
double-double.
§1 New running footer for IEEE drafts substituted for published 754 copyright notice.
Rationale: comply with IEEE rules.
11 April 2001
§4 SCOPE and PURPOSE defined.
Rationale: previous intent was not universally understood.
OPEN ISSUE: too narrow a purpose? Is uniqueness specified and achievable?
OPEN ISSUE: merge the new PURPOSE: with the Foreword; merge the new and existing SCOPE: to
remove redundancy.
Copyright © 2003 by the Institute of Electrical and Electronics Engineers, Inc. This document is an unapproved
draft of a proposed IEEE-SA Standard - USE AT YOUR OWN RISK. See statement on page 1.
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