Use C2x return value from getpayload of non-NaN (bug 26073).

In TS 18661-1, getpayload had an unspecified return value for a
non-NaN argument, while C2x requires the return value -1 in that case.

This patch implements the return value of -1.  I don't think this is
worth having a new symbol version that's an alias of the old one,
although occasionally we do that in such cases where the new function
semantics are a refinement of the old ones (to avoid programs relying
on the new semantics running on older glibc versions but not behaving
as intended).

Tested for x86_64 and x86; also ran math/ tests for aarch64 and
powerpc.

1 files changed, 4 insertions, 3 deletions

diff --git a/manual/arith.texi b/manual/arith.texi
index 89c2c064f1..75eaf67fe7 100644
--- a/manual/arith.texi
+++ b/manual/arith.texi
@@ -1895,9 +1895,10 @@ propagated from NaN inputs to the result of a floating-point
 operation.  These functions, defined by TS 18661-1:2014 and TS
 18661-3:2015, return the payload of the NaN pointed to by @var{x}
 (returned as a positive integer, or positive zero, represented as a
-floating-point number); if @var{x} is not a NaN, they return an
-unspecified value.  They raise no floating-point exceptions even for
-signaling NaNs.
+floating-point number); if @var{x} is not a NaN, they return
+@minus{}1.  They raise no floating-point exceptions even for signaling
+NaNs.  (The return value of @minus{}1 for an argument that is not a
+NaN is specified in C2x; the value was unspecified in TS 18661.)
 @end deftypefun
 
 @deftypefun int setpayload (double *@var{x}, double @var{payload})