// An isogram is a word that has no repeating letters, consecutive or non-consecutive. Implement a function that determines whether a string that contains only letters is an isogram. Assume the empty string is an isogram. Ignore letter case.

#include <stdbool.h>
#include <stdint.h>
#include <string.h>

bool IsIsogram(const char *str)
{
    uint32_t bits;
    size_t   idx;

    for(bits = idx = 0; idx < strlen(str); ++idx)
        if(idx == __builtin_popcountl(bits |= 1L << (str[idx] & 0x1f)))
            return false;
    return true;
}