From 7ec903e028271d029818378fd60ddaf6b76b89ac Mon Sep 17 00:00:00 2001 From: Joseph Myers Date: Mon, 17 Jun 2024 16:31:49 +0000 Subject: Implement C23 exp2m1, exp10m1 C23 adds various function families originally defined in TS 18661-4. Add the exp2m1 and exp10m1 functions (exp2(x)-1 and exp10(x)-1, like expm1). As with other such functions, these use type-generic templates that could be replaced with faster and more accurate type-specific implementations in future. Test inputs are copied from those for expm1, plus some additions close to the overflow threshold (copied from exp2 and exp10) and also some near the underflow threshold. exp2m1 has the unusual property of having an input (M_MAX_EXP) where whether the function overflows (under IEEE semantics) depends on the rounding mode. Although these could reasonably be XFAILed in the testsuite (as we do in some cases for arguments very close to a function's overflow threshold when an error of a few ulps in the implementation can result in the implementation not agreeing with an ideal one on whether overflow takes place - the testsuite isn't smart enough to handle this automatically), since these functions aren't required to be correctly rounding, I made the implementation check for and handle this case specially. The Makefile ordering expected by lint-makefiles for the new functions is a bit peculiar, but I implemented it in this patch so that the test passes; I don't know why log2 also needed moving in one Makefile variable setting when it didn't in my previous patches, but the failure showed a different place was expected for that function as well. The powerpc64le IFUNC setup seems not to be as self-contained as one might hope; it shouldn't be necessary to add IFUNCs for new functions such as these simply to get them building, but without setting up IFUNCs for the new functions, there were undefined references to __GI___expm1f128 (that IFUNC machinery results in no such function being defined, but doesn't stop include/math.h from doing the redirection resulting in the exp2m1f128 and exp10m1f128 implementations expecting to call it). Tested for x86_64 and x86, and with build-many-glibcs.py. --- manual/math.texi | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+) (limited to 'manual') diff --git a/manual/math.texi b/manual/math.texi index 18b7173bf0..e4f9122609 100644 --- a/manual/math.texi +++ b/manual/math.texi @@ -740,6 +740,36 @@ near zero---a case where @code{exp (@var{x}) - 1} would be inaccurate owing to subtraction of two numbers that are nearly equal. @end deftypefun +@deftypefun double exp2m1 (double @var{x}) +@deftypefunx float exp2m1f (float @var{x}) +@deftypefunx {long double} exp2m1l (long double @var{x}) +@deftypefunx _FloatN exp2m1fN (_Float@var{N} @var{x}) +@deftypefunx _FloatNx exp2m1fNx (_Float@var{N}x @var{x}) +@standards{TS 18661-4:2015, math.h} +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} +These functions return a value equivalent to @code{exp2 (@var{x}) - 1}. +They are computed in a way that is accurate even if @var{x} is +near zero---a case where @code{exp2 (@var{x}) - 1} would be inaccurate owing +to subtraction of two numbers that are nearly equal. + +The @code{exp2m1} functions are from TS 18661-4:2015. +@end deftypefun + +@deftypefun double exp10m1 (double @var{x}) +@deftypefunx float exp10m1f (float @var{x}) +@deftypefunx {long double} exp10m1l (long double @var{x}) +@deftypefunx _FloatN exp10m1fN (_Float@var{N} @var{x}) +@deftypefunx _FloatNx exp10m1fNx (_Float@var{N}x @var{x}) +@standards{TS 18661-4:2015, math.h} +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} +These functions return a value equivalent to @code{exp10 (@var{x}) - 1}. +They are computed in a way that is accurate even if @var{x} is +near zero---a case where @code{exp10 (@var{x}) - 1} would be inaccurate owing +to subtraction of two numbers that are nearly equal. + +The @code{exp10m1} functions are from TS 18661-4:2015. +@end deftypefun + @deftypefun double log1p (double @var{x}) @deftypefunx float log1pf (float @var{x}) @deftypefunx {long double} log1pl (long double @var{x}) -- cgit 1.4.1