Possible defect in <math.h>: ilogb inconsistent with lrint, lround

Document: WG14 N1595

Possible defect in <math.h>: ilogb inconsistent with lrint, lround

Submitter: Fred J. Tydeman (USA)
Submission Date: 2012-1-11
Subject: ilogb inconsistent with lrint, lround

For the case of converting a large finite value to an integer value, lrint and lround have one set of requirements, while ilogb has another set. This is inconsistent.

Both 7.12.9.5 The lrint and llrint functions and 7.12.9.7 The lround and llround functions have:

If the rounded value is outside the range of the return type, the numeric result is unspecified and a domain error or range error may occur.

While 7.12.6.5 The ilogb functions has:

If the correct value is outside the range of the return type, the numeric result is unspecified.

I believe that the following changes to C11 should be done.

7.12.6.5 The ilogb functions:
Change to: If the correct value is outside the range of the return type, the numeric result is unspecified and a domain error or range error may occur.