#include <stdio.h>
#include <stdint.h>
#include <inttypes.h>
 
int main(void)
{
 
int8_t n[] = {'9', '8', '7', '6', '5', '4', '3', '2'};
uint64_t* a = (uint64_t *)n;
*a =((*a & 0x0F000F000F000F00)>>8) +\
    ((*a & 0x000F000F000F000F)*10);
 
*a = 1000000 * ((*a >> 0 ) & 0xFF) +\
       10000 * ((*a >> 16) & 0xFF) +\
         100 * ((*a >> 32) & 0xFF) +\
               ((*a >> 48) & 0xFF);
//little-endian only. Можно переделать под big-endian
 
printf("%"PRIu64, *a);
 
return 0;
}

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