Changeset 4c4e444

Timestamp:

Apr 13, 2021, 5:38:34 PM (3 years ago)

Author:

Peter A. Buhr <pabuhr@…>

Branches:

ADT, arm-eh, ast-experimental, enum, forall-pointer-decay, jacob/cs343-translation, master, new-ast-unique-expr, pthread-emulation, qualifiedEnum

Children:

fd4c009

Parents:

88ac8672

Message:

add log2 for integers using clz instruction

File:

• libcfa/src/math.hfa (modified) (2 diffs)

libcfa/src/math.hfa

@@ -10 +10 @@
 // Created On       : Mon Apr 18 23:37:04 2016
 // Last Modified By : Peter A. Buhr
-// Last Modified On : Mon Aug 24 08:56:20 2020
-// Update Count     : 126
+// Last Modified On : Mon Apr 12 18:35:39 2021
+// Update Count     : 131
 //
 
@@ -100 +100 @@
         long double _Complex log( long double _Complex x ) { return clogl( x ); }
 
+        // O(1) polymorphic integer log2, using clz, which returns the number of leading 0-bits, starting at the most
+        // significant bit (single instruction on x86)
+        int log2( unsigned int n ) { return n == 0 ? -1 : sizeof(n) * __CHAR_BIT__ - 1 - __builtin_clz( n ); }
+        long int log2( unsigned long int n ) { return n == 0 ? -1 : sizeof(n) * __CHAR_BIT__ - 1 - __builtin_clzl( n ); }
+        long long int log2( unsigned long long int n ) { return n == 0 ? -1 : sizeof(n) * __CHAR_BIT__ - 1 - __builtin_clzl( n ); }
         float log2( float x ) { return log2f( x ); }
         // extern "C" { double log2( double ); }