Re^4: Map a string to an array

[BrowserUk]

(And BTW, congratulations on being able to work with a system having at least 128 Terabytes of system RAM — or do I misinterpret the reference address of 0x7ffafc013bf8?)

With virtual memory, heap does not have to be contiguous.

This C program allocates a single page of memory starting at the 4GB base address and then doubles the base address each time until it fails:

#define  _CRT_SECURE_NO_WARNINGS
#include <windows.h>
#include <conio.h>
#include <time.h>
#include "debug.h"
#include "mytypes.h"

int main( int argc, char **argv ) {
    U64 size = 4096, base = 4294967296;
    char *p;

    while( 1 ) {
        char *p = VirtualAllocEx(
            GetCurrentProcess(),
            (VOID*)base, size,
            MEM_RESERVE | MEM_COMMIT, PAGE_READWRITE
        );
        DIEIF( p == NULL );
        printf( "4k allocated at:%16p (%30I64d)\n", p, 0+p );
        _getch();
        base *= 2;
    }
    exit( 0 );
}

I only have 8GB of ram, but the last time the above succeeds:

C:\test>vmem3
4k allocated at:0000000100000000 (                    4294967296)
4k allocated at:0000000200000000 (                    8589934592)
4k allocated at:0000000400000000 (                   17179869184)
4k allocated at:0000000800000000 (                   34359738368)
4k allocated at:0000001000000000 (                   68719476736)
4k allocated at:0000002000000000 (                  137438953472)
4k allocated at:0000004000000000 (                  274877906944)
4k allocated at:0000008000000000 (                  549755813888)
4k allocated at:0000010000000000 (                 1099511627776)
4k allocated at:0000020000000000 (                 2199023255552)
4k allocated at:0000040000000000 (                 4398046511104)
[ 1916] vmem3.c(18):p == NULL
        failed with error 87 (The parameter is incorrect)

It allocated a page at a base address that is 4096 GB. At that point the process is only using 668k of memory.

4096GB is 2^42 which reflects that my 64-bit processor actually only has a 44-bit virtual address space.