Simple utility calculating some basic heap chunk's characteristics like chunk size, bin index and it's range - according to original Doug Lea's heap allocator implementation. Useful while grasping Heap Overflow binning conditions.

request2size.c

// vim: ai:si:ts=2:sw=2
#include <stdio.h>

#define INTERNAL_SIZE_T size_t
#define SIZE_SZ sizeof(INTERNAL_SIZE_T)
#define MINSIZE 2*SIZE_SZ

#define MALLOC_ALIGNMENT ( SIZE_SZ + SIZE_SZ )
#define MALLOC_ALIGN_MASK ( MALLOC_ALIGNMENT - 1 )

#define request2size(req, nb) \
 ((nb = (req) + (SIZE_SZ + MALLOC_ALIGN_MASK)),\
  ((long)nb <= 0 || nb < (INTERNAL_SIZE_T) (req) \
   ? (1) \
   : ((nb < (MINSIZE + MALLOC_ALIGN_MASK) \
           ? (nb = MINSIZE) : (nb &= ~MALLOC_ALIGN_MASK)), 0)))

#define bin_index(sz)                                                     \
((((unsigned long)(sz) >> 9) ==    0) ?       ((unsigned long)(sz) >>  3):\
 (((unsigned long)(sz) >> 9) <=    4) ?  56 + ((unsigned long)(sz) >>  6):\
 (((unsigned long)(sz) >> 9) <=   20) ?  91 + ((unsigned long)(sz) >>  9):\
 (((unsigned long)(sz) >> 9) <=   84) ? 110 + ((unsigned long)(sz) >> 12):\
 (((unsigned long)(sz) >> 9) <=  340) ? 119 + ((unsigned long)(sz) >> 15):\
 (((unsigned long)(sz) >> 9) <= 1364) ? 124 + ((unsigned long)(sz) >> 18):\
                                        126)

void bin_range(unsigned long sz, unsigned long *bmin, unsigned long *bmax) {
	unsigned long d = (unsigned long)(sz) >> 9;
	if( d == 0 )       *bmin = ((unsigned long)(sz >> 3) * (1 << 3)), *bmax = (*bmin + (1 << 3));
	else if( d <= 4 )  *bmin = ((unsigned long)(sz >> 6) * (1 << 6)), *bmax = (*bmin + (1 << 6));
	else if( d <= 20 )  *bmin = ((unsigned long)(sz >> 9) * (1 << 9)), *bmax = (*bmin + (1 << 9));
	else if( d <= 84 )  *bmin = ((unsigned long)(sz >> 12) * (1 << 12)), *bmax = (*bmin + (1 << 12));
	else if( d <= 340 )  *bmin = ((unsigned long)(sz >> 15) * (1 << 15)), *bmax = (*bmin + (1 << 15));
	else if( d <= 1364 )  *bmin = ((unsigned long)(sz >> 18) * (1 << 18)), *bmax = (*bmin + (1 << 18));
	else *bmin = 0, *bmax = 0;
}

int main( int argc, char **argv) {

	if (argc != 2) {
		printf("Usage: %s <size>\n", argv[0]);
		return 0;
	}

	unsigned long size = atoi(argv[1]);	
	unsigned long nb, min, max;

	request2size(size, nb);
	bin_range(size, &min, &max);

	printf("Request:\t%d\n"
		"Size:\t\t%d\n"
		"Bin index:\t%d (%d-%d)\n",
		size, nb, bin_index(nb), min, max);
}