Changeset 4c4e444


Ignore:
Timestamp:
Apr 13, 2021, 5:38:34 PM (2 months ago)
Author:
Peter A. Buhr <pabuhr@…>
Branches:
arm-eh, jacob/cs343-translation, master
Children:
fd4c009
Parents:
88ac867
Message:

add log2 for integers using clz instruction

File:
1 edited

Legend:

Unmodified
Added
Removed
  • libcfa/src/math.hfa

    r88ac867 r4c4e444  
    1010// Created On       : Mon Apr 18 23:37:04 2016
    1111// Last Modified By : Peter A. Buhr
    12 // Last Modified On : Mon Aug 24 08:56:20 2020
    13 // Update Count     : 126
     12// Last Modified On : Mon Apr 12 18:35:39 2021
     13// Update Count     : 131
    1414//
    1515
     
    100100        long double _Complex log( long double _Complex x ) { return clogl( x ); }
    101101
     102        // O(1) polymorphic integer log2, using clz, which returns the number of leading 0-bits, starting at the most
     103        // significant bit (single instruction on x86)
     104        int log2( unsigned int n ) { return n == 0 ? -1 : sizeof(n) * __CHAR_BIT__ - 1 - __builtin_clz( n ); }
     105        long int log2( unsigned long int n ) { return n == 0 ? -1 : sizeof(n) * __CHAR_BIT__ - 1 - __builtin_clzl( n ); }
     106        long long int log2( unsigned long long int n ) { return n == 0 ? -1 : sizeof(n) * __CHAR_BIT__ - 1 - __builtin_clzl( n ); }
    102107        float log2( float x ) { return log2f( x ); }
    103108        // extern "C" { double log2( double ); }
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