[Bug libc/17803] New: scalblnl differs from scabnl and ldexpl (with radix 2)

[walter.mascarenhas at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=17803

            Bug ID: 17803
           Summary: scalblnl differs from scabnl and ldexpl (with radix 2)
           Product: glibc
           Version: 2.19
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: walter.mascarenhas at gmail dot com
                CC: drepper.fsp at gmail dot com

Created attachment 8046
  --> https://sourceware.org/bugzilla/attachment.cgi?id=8046&action=edit
test case illustrating the problem

It would be convenient if the functions scalbnl, ldexpl (when the radix = 2)
and scalblnl delivered the same results when the exponents were within the
common range supported by these functions. However, when rounding to nearest,
scalblnl may deliver a result that differs from the one obtained by ldexpl and
scalbnl
(please see the enclosed main.cc file)

I do not have a copy of the ISO/IEC 60559 standard and therefore I cannot tell
whether this behavior is compatible with the standard. However, there is much
confusion this point in some webpages, and it would be nice if glibc's
documentation contained a detailed description of the outupt in all possible
cases.

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