Add more tests for corner cases of log1p and expm1. Add handling of infinite arguments to log1p such that log1p(inf) = inf.

2 files changed, 4 insertions, 2 deletions

diff --git a/Eigen/src/Core/MathFunctions.h b/Eigen/src/Core/MathFunctions.h
index fcf62011e..fbec39d83 100644
--- a/Eigen/src/Core/MathFunctions.h
+++ b/Eigen/src/Core/MathFunctions.h
@@ -551,7 +551,8 @@ namespace std_fallback {
     Scalar x1p = RealScalar(1) + x;
     Scalar log_1p = log(x1p);
     const bool is_small = numext::equal_strict(x1p, Scalar(1));
-    return is_small ? x : x * (log_1p / (x1p - RealScalar(1)));
+    const bool is_inf = numext::equal_strict(x1p, log_1p);
+    return (is_small || is_inf) ? x : x * (log_1p / (x1p - RealScalar(1)));
   }
 }
 
diff --git a/Eigen/src/Core/arch/Default/GenericPacketMathFunctions.h b/Eigen/src/Core/arch/Default/GenericPacketMathFunctions.h
index 505a0eec8..0fc673e12 100644
--- a/Eigen/src/Core/arch/Default/GenericPacketMathFunctions.h
+++ b/Eigen/src/Core/arch/Default/GenericPacketMathFunctions.h
@@ -137,8 +137,9 @@ Packet generic_plog1p(const Packet& x)
   Packet xp1 = padd(x, one);
   Packet small_mask = pcmp_eq(xp1, one);
   Packet log1 = plog(xp1);
+  Packet inf_mask = pcmp_eq(xp1, log1);
   Packet log_large = pmul(x, pdiv(log1, psub(xp1, one)));
-  return pselect(small_mask, x, log_large);
+  return pselect(por(small_mask, inf_mask), x, log_large);
 }
 
 /** \internal \returns exp(x)-1 computed using W. Kahan's formula.