[flang-commits] [PATCH] D151272: [flang] Fix SPACING() of very small values

[Peter Klausler via Phabricator via flang-commits]

klausler created this revision.
klausler added a reviewer: vdonaldson.
klausler added a project: Flang.
Herald added subscribers: sunshaoce, jdoerfert.
Herald added a project: All.
klausler requested review of this revision.

SPACING() must return TINY() for zero arguments (which we do)
and also for subnormal values smaller than TINY() in absolute value,
which we get wrong.  Fix folding and the runtime.


https://reviews.llvm.org/D151272

Files:
  flang/lib/Evaluate/real.cpp
  flang/runtime/numeric.cpp
  flang/test/Evaluate/fold-spacing.f90


Index: flang/test/Evaluate/fold-spacing.f90
===================================================================
--- flang/test/Evaluate/fold-spacing.f90
+++ flang/test/Evaluate/fold-spacing.f90
@@ -7,6 +7,7 @@
   logical, parameter :: test_4 = spacing(0.) == tiny(0.)
   logical, parameter :: test_5 = spacing(tiny(0.)) == 1.e-45
   logical, parameter :: test_6 = spacing(8388608.) == 1.
+  logical, parameter :: test_7 = spacing(spacing(tiny(.0))) == tiny(0.)
   logical, parameter :: test_11 = rrspacing(3.0) == scale(0.75, 24)
   logical, parameter :: test_12 = rrspacing(-3.0) == scale(0.75, 24)
   logical, parameter :: test_13 = rrspacing(3.0d0) == scale(0.75, 53)
Index: flang/runtime/numeric.cpp
===================================================================
--- flang/runtime/numeric.cpp
+++ flang/runtime/numeric.cpp
@@ -239,8 +239,9 @@
     // subnormal.
     return std::numeric_limits<T>::min(); // 0 -> TINY(x)
   } else {
-    return std::ldexp(
-        static_cast<T>(1.0), std::ilogb(x) + 1 - PREC); // 2**(e-p)
+    T result{
+        std::ldexp(static_cast<T>(1.0), std::ilogb(x) + 1 - PREC)}; // 2**(e-p)
+    return result == 0 ? /*TINY(x)*/ std::numeric_limits<T>::min() : result;
   }
 }
 
Index: flang/lib/Evaluate/real.cpp
===================================================================
--- flang/lib/Evaluate/real.cpp
+++ flang/lib/Evaluate/real.cpp
@@ -745,12 +745,12 @@
     return *this;
   } else if (IsInfinite()) {
     return NotANumber();
-  } else if (IsZero()) {
-    return TINY();
+  } else if (IsZero() || IsSubnormal()) {
+    return TINY(); // mandated by standard
   } else {
     Real result;
     result.Normalize(false, Exponent(), Fraction::MASKR(1));
-    return result;
+    return result.IsZero() ? TINY() : result;
   }
 }
 


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