[lmi-commits] [lmi] master 06e5af60 2/2: Fix defect introduced 20220527T2230Z: negated integer minimum

[Greg Chicares]

branch: master
commit 06e5af6027b2b7fc87bb139827ec0b893e3f2cac
Author: Gregory W. Chicares <gchicares@sbcglobal.net>
Commit: Gregory W. Chicares <gchicares@sbcglobal.net>

    Fix defect introduced 20220527T2230Z: negated integer minimum
    
    Commit bff73872e59f44 of 20220527T2230Z changed a lower bound from
    -max() to -lowest(): the negative of an integer minimum.
    
    Although the test is used only for floating-point types, this lowest()
    is an integer limit:
      constexpr auto z1lo = std::numeric_limits<long long int>::lowest();
    But an integer lowest() is the negative of an integral power of two,
    and negating it reliably preserves its value in two's-complement
    arithmetic (thus, for int8_t, negating -128 yields -128), though in
    C and C++ it's UB. Naturally gcc returns -2^63, whose negative is
    itself, so no failing unit test can be devised.
---
 tn_range.tpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tn_range.tpp b/tn_range.tpp
index 8495223d..fd74be98 100644
--- a/tn_range.tpp
+++ b/tn_range.tpp
@@ -204,7 +204,7 @@ namespace
             return
                    -z0   < t
                 &&         t < z0
-                && -z1lo < t
+                &&  z1lo < t
                 &&         t < z1hi
                 && t == static_cast<long long int>(t)
                 ;