String to byte array (hex base). String must not contain any space

strtoba_h.c

#include <stdio.h>
#include <ctype.h>

static inline
int hex_alpha_only(const char* string)
{
	for(;*string;*string++) {
		if(!(   (*string >= 'a' && *string <= 'f') ||
		        (*string >= 'A' && *string <= 'F') ||
		        (*string >= '0' && *string <= '9') 
			)) //if...end
		return 0;
	}

	return 1;
}

int strtoba_h(const char* from, unsigned char* target_array, const size_t target_array_size)
{
	if(!hex_alpha_only(from))
		return -1;
	
	for(size_t i=0;i<target_array_size;i++) {
		sscanf(from,"%2hhx", &target_array[i]);
		from += 2;
	}
	
	return 0;
}