Handy memory-manipulation functions that don't exist in the standard

memtools.c

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

// Copy a byte pattern into memory, repeating src if dest_len > src_len
void *memwrap(void *dest, const void *src, size_t dest_len, size_t src_len){
	if((dest == NULL) || (src == NULL) || (dest_len == 0U) ||
	   (src_len == 0U) || (dest == src)){
		goto return_early;
	}
	if(dest_len <= src_len){
		memmove(dest, src, dest_len);
	}else{
		size_t i;
		uint8_t *dest_bytes = dest;
		for(i = 0; i < (dest_len - src_len); i += src_len){
			memmove(&dest_bytes[i], src, src_len);
		}
		memmove(&dest_bytes[i], src, dest_len - i);
	}
	return_early:
	return dest;
}

#define vd_idx(a, sz, x) ((void*)((uint8_t*)(a) + (sz) * (x)))

// Swap two regions of memory that are each at least num_bytes bytes long
void memswap(void *a, void *b, size_t num_bytes){
	if((a == NULL) || (b == NULL) || (num_bytes == 0U))
		goto return_early;
	for(size_t i = 0; i < num_bytes; ++i){
		uint8_t tmp = *(uint8_t*)vd_idx(a, 1, i);
		memcpy(vd_idx(a, 1, i), vd_idx(b, 1, i), 1);
		memcpy(vd_idx(b, 1, i), &tmp, 1);
	}
	return_early:
	return;
}