Digest for comp.lang.c++@googlegroups.com - 2 updates in 2 topics

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• A UTM halt decider <is> a pure function of its inputs (halt deciding) - 1 Update
• std::vector<>::capacity()-growth - 1 Update

A UTM halt decider <is> a pure function of its inputs (halt deciding)

olcott <NoOne@NoWhere.com>: Mar 22 04:40PM -0500 On 3/22/2021 2:50 PM, Malcolm McLean wrote: > on its call context. If fundamentally you've just passed the global > flag , but disguised it cleverly, then that would also be interesting in its own > right, but as a trick rather than as a contribution to computer theory.   A global UTM / x86 emulator derives an execution trace incrementally one simulated instruction at a time that is a pure function of its inputs.   No machine descriptions are simulated outside of the scope of this global UTM / x86 emulator.   After the simulation of each instruction UTM / x86 emulator invokes a halt decider that derives a return value to the simulator EXECUTING / HALTED / WILL_NOT_HALT as a pure function of its input execution trace.   The global UTM / x86 emulator continues simulating its input while this return value from the halt decider is EXECUTING.   http://www.liarparadox.org/Halting_problem_undecidability_and_infinite_recursion.pdf   -- Copyright 2021 Pete Olcott   "Great spirits have always encountered violent opposition from mediocre minds." Einstein

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std::vector<>::capacity()-growth

Bonita Montero <Bonita.Montero@gmail.com>: Mar 22 06:53PM +0100 Java does the same:   import java.util.ArrayList; import java.lang.reflect.Field;   public class ArrayLIstGrowth { public static void main( String[] args ) { ArrayList<Integer> al = new ArrayList<Integer>(); int cap = getCapacity( al ); for( int i = 0; i != 1000000; ++i ) { al.add( i ); int newCap = getCapacity( al ); if( newCap != cap ) { System.out.printf( "%d - %d\n", i, newCap ); cap = newCap; }   } } static int getCapacity( ArrayList<?> al ) { try { if( field == null ) { field = ArrayList.class.getDeclaredField( "elementData" ); field.setAccessible( true ); } return ((Object[])field.get( al )).length; } catch( NoSuchFieldException nsfe ) { return -1; } catch( IllegalAccessException iae ) { return -1; } } static Field field = null; }   0 - 10 10 - 15 15 - 22 22 - 33 33 - 49 49 - 73 73 - 109 109 - 163 163 - 244 244 - 366 366 - 549 549 - 823 823 - 1234 1234 - 1851 1851 - 2776 2776 - 4164 4164 - 6246 6246 - 9369 9369 - 14053 14053 - 21079 21079 - 31618 31618 - 47427 47427 - 71140 71140 - 106710 106710 - 160065 160065 - 240097 240097 - 360145 360145 - 540217 540217 - 810325 810325 - 1215487

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