Hi! On Sat, Aug 15, 2020 at 12:10:42PM +0100, Roger Sayle wrote: > I'll quote Joseph Myers (many thanks) who describes things clearly as: > > (a) When both arguments are NaNs, the return value should be a qNaN, > > but sometimes it is an sNaN if at least one argument is an sNaN.
Where is this defined? I can't find it in C11, in 18661, and of course it isn't what GCC does (it requires -fsignaling to even acknowledge the existence of signaling NaNs :-) ) > > (b) Under TS 18661-1 semantics, if either argument is an sNaN then the > > result should be a qNaN (whereas if one argument is a qNaN and the > > other is not a NaN, the result should be the non-NaN argument). I cannot find that first part. > if (tree_expr_maybe_signaling_nan_p (arg0) || > tree_expr_maybe_signaling_nan_p (arg1)) > return RECURSE (arg0) && RECURSE (arg1); This new function returns false if !HONOR_SNANS, so this looks good :-) > +bool > +tree_expr_maybe_signaling_nan_p (const_tree x) > + case MIN_EXPR: > + case MAX_EXPR: > + return tree_expr_maybe_signaling_nan_p (TREE_OPERAND (x, 0)) > + || tree_expr_maybe_signaling_nan_p (TREE_OPERAND (x, 1)); Can those ever return a SNaN? What does GCC do for FP_SNANS_ALWAYS_SIGNAL? All looks good to me except the SNaN stuff (which may be just me not understanding it). I find "maybe_" stuff very hard to read and understand btw, but there may be no escaping that :-/ Thanks, Segher
