memcat.c

#include "memcat.h"

#define MIN(a,b) ((a) < (b) ? (a) : (b))

size_t memcat(uint8_t * dst,
              struct memdesc * descriptors,
              size_t descriptor_count,
              size_t max_len)
{
  size_t remaining = max_len;
  uint8_t * next = dst;

  for (size_t i = 0; i < descriptor_count; i++)
  {
    struct memdesc * desc = &descriptors[i];
    size_t copy_len = MIN(remaining, desc->length);

    memcpy(next, desc->ptr, copy_len);
    next += copy_len;
    remaining -= copy_len;

    if (remaining <= 0)
      break;
  }

  return (max_len - remaining);
}

memcat.h

#ifndef memcat_h
#define memcat_h

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

#define OBJ_MEMDESC(o) { sizeof(o), (uint8_t*)&(o) }
#define DESC_COUNT(descs) (sizeof(descs) / sizeof((descs)[0]))

struct memdesc
{
  size_t length;
  uint8_t * ptr;
};

/*
 * memcat - concatenate several regions of memory into one region
 *
 *  dst - the destination pointer
 *  descriptors - an ordered array of memory descriptors to be copied
 *  descriptor_count - the number of descriptors in the array
 *  max_len - the maximum number of bytes to copy into dst
 */
size_t memcat(uint8_t * dst,
              struct memdesc * descriptors,
              size_t descriptor_count,
              size_t max_len);

#endif /* memcat_h */