LibM: Add ilogb and logb

Author: https://github.com/RealKC
Commit: https://github.com/SerenityOS/serenity/commit/352b383280d
Pull-request: https://github.com/SerenityOS/serenity/pull/5688
Issue: https://github.com/SerenityOS/serenity/issues/4282
Reviewed-by: https://github.com/ADKaster
Reviewed-by: https://github.com/BenWiederhake
Reviewed-by: https://github.com/awesomekling

Userland/Libraries/LibM/math.cpp

@@ -243,6 +243,26 @@ static FloatType internal_nextafter(FloatType x, bool up)
     return extractor.d;
 }
 
+template<typename FloatT>
+static int internal_ilogb(FloatT x) NOEXCEPT
+{
+    if (x == 0)
+        return FP_ILOGB0;
+
+    if (isnan(x))
+        return FP_ILOGNAN;
+
+    if (!isfinite(x))
+        return INT_MAX;
+
+    using Extractor = FloatExtractor<FloatT>;
+
+    Extractor extractor;
+    extractor.d = x;
+
+    return (int)extractor.exponent - Extractor::exponent_bias;
+}
+
 extern "C" {
 
 double trunc(double x) NOEXCEPT
@@ -547,6 +567,36 @@ double fabs(double value) NOEXCEPT
     return value < 0 ? -value : value;
 }
 
+int ilogbl(long double x) NOEXCEPT
+{
+    return internal_ilogb(x);
+}
+
+int ilogb(double x) NOEXCEPT
+{
+    return internal_ilogb(x);
+}
+
+int ilogbf(float x) NOEXCEPT
+{
+    return internal_ilogb(x);
+}
+
+long double logbl(long double x) NOEXCEPT
+{
+    return ilogbl(x);
+}
+
+double logb(double x) NOEXCEPT
+{
+    return ilogb(x);
+}
+
+float logbf(float x) NOEXCEPT
+{
+    return ilogbf(x);
+}
+
 double log2(double x) NOEXCEPT
 {
     double ret = 0.0;

Userland/Libraries/LibM/math.h

@@ -26,6 +26,7 @@
 
 #pragma once
 
+#include <limits.h>
 #include <sys/cdefs.h>
 
 #if __cplusplus >= 201103L
@@ -128,6 +129,15 @@ float ldexpf(float, int exp) NOEXCEPT;
 double pow(double x, double y) NOEXCEPT;
 float powf(float x, float y) NOEXCEPT;
 
+#define FP_ILOGB0 INT_MIN
+#define FP_ILOGNAN INT_MAX
+
+int ilogbl(long double) NOEXCEPT;
+int ilogb(double) NOEXCEPT;
+int ilogbf(float) NOEXCEPT;
+long double logbl(long double) NOEXCEPT;
+double logb(double) NOEXCEPT;
+float logbf(float) NOEXCEPT;
 double log2(double) NOEXCEPT;
 float log2f(float) NOEXCEPT;
 long double log2l(long double) NOEXCEPT;