Improve accuracy

kimwalisch · Feb 17, 2024 · 9e140d3 · 9e140d3
1 parent 1cbd7c6
commit 9e140d3
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Showing 2 changed files with 8 additions and 4 deletions.
diff --git a/src/LogarithmicIntegral.cpp b/src/LogarithmicIntegral.cpp
@@ -226,7 +226,8 @@ namespace primecount {
 int64_t Li(int64_t x)
 {
 #if defined(HAVE_FLOAT128)
-  if (x > 1e10 && std::log2(x) >= std::numeric_limits<long double>::digits)
+  double long_double_mantissa_bits = std::numeric_limits<long double>::digits;
+  if (x > 1e10 && std::log2(x) >= long_double_mantissa_bits - 3)
     return (int64_t) ::Li((__float128) x);
 #endif
   return (int64_t) ::Li((long double) x);
@@ -263,7 +264,8 @@ int64_t Li_inverse(int64_t x)
 int128_t Li(int128_t x)
 {
 #if defined(HAVE_FLOAT128)
-  if (x > 1e10 && std::log2(x) >= std::numeric_limits<long double>::digits)
+  double long_double_mantissa_bits = std::numeric_limits<long double>::digits;
+  if (x > 1e10 && std::log2(x) >= long_double_mantissa_bits - 3)
     return (int128_t) ::Li((__float128) x);
 #endif
   return (int128_t) ::Li((long double) x);

diff --git a/src/RiemannR.cpp b/src/RiemannR.cpp
@@ -550,7 +550,8 @@ namespace primecount {
 int64_t RiemannR(int64_t x)
 {
 #if defined(HAVE_FLOAT128)
-  if (x > 1e10 && std::log2(x) >= std::numeric_limits<long double>::digits)
+  double long_double_mantissa_bits = std::numeric_limits<long double>::digits;
+  if (x > 1e10 && std::log2(x) >= long_double_mantissa_bits - 3)
     return (int64_t) ::RiemannR((__float128) x);
 #endif
   return (int64_t) ::RiemannR((long double) x);
@@ -587,7 +588,8 @@ int64_t RiemannR_inverse(int64_t x)
 int128_t RiemannR(int128_t x)
 {
 #if defined(HAVE_FLOAT128)
-  if (x > 1e10 && std::log2(x) >= std::numeric_limits<long double>::digits)
+  double long_double_mantissa_bits = std::numeric_limits<long double>::digits;
+  if (x > 1e10 && std::log2(x) >= long_double_mantissa_bits - 3)
     return (int128_t) ::RiemannR((__float128) x);
 #endif
   return (int128_t) ::RiemannR((long double) x);