Date: Thu, 18 Sep 2014 19:55:47 +0200 From: Szabolcs Nagy <nsz@...t70.net> To: musl@...ts.openwall.com Subject: Re: [PATCH] Make musl math depend less on libgcc builtins * Sergey Dmitrouk <sdmitrouk@...esssoftek.com> [2014-09-18 17:28:40 +0300]: > On Thu, Sep 11, 2014 at 07:11:23AM -0700, Szabolcs Nagy wrote: > > on a correct implementation ==, != are quiet, but <,>,<=,>= > > raise invalid if any of the operands are nan > > I wanted to get some details on this, but failed to find relevant > sections of C99/IEEE754 standards. I see C99 referring to IEEE754, is > it in "5.11 Details of comparison predicates" section of IEEE754? > Could you please point me to section(s) I'm apparently missing? yes ieee754-2008 5.11 i think it is clear: there are tables showing all the predicates and to which "traditional names and symbols" they should map. table 5.1 shows ==, != as quiet comparisions, table 5.2 shows <,> operations as signaling and the text mentions that the quiet operations in table 5.3 are for applications which want to explicitly handle quiet nans that way the text in iso C F.3 is not very detailed about the mapping but gives hints: The relational and equality operators provide IEC 60559 comparisons. IEC 60559 identifies a need for additional comparison predicates to facilitate writing code that accounts for NaNs. The comparison macros (isgreater, isgreaterequal, isless, islessequal, islessgreater, and isunordered) in <math.h> supplement the language operators to address this need. The islessgreater and isunordered macros provide respectively a quiet version of the <> predicate and the unordered predicate recommended in the Appendix to IEC 60559. the <,> predicates need a quiet version because the default is not quiet, but == and != dont since they are already quiet the precise mapping will be spelled out in more detail in TS 18661, http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1778.pdf see "table - 1 operation binding" (the latest version seems to be password protected, sigh..)
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