/* RAM waster */
/* this program is given into the public domain by its author,
   Robert Clausecker. 2016-09-10. */

#include <ctype.h>
#include <errno.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <limits.h>

static size_t compute_amount(const char*);

extern int
main(int argc, char *argv[])
{
	size_t amount;
	char *memory;

	if (argc != 2) {
		fprintf(stderr, "Usage: %s amount-to-waste\n", argv[0]);
		fprintf(stderr, "suffixes kmgtpe are supported.\n");
		fprintf(stderr, "lower case suffixes are binary, upper case decimal\n");
		return (EXIT_FAILURE);
	}

	amount = compute_amount(argv[1]);
	memory = malloc(amount);
	if (memory == NULL) {
		fprintf(stderr, "%s is too much memory!\n", argv[1]);
		return (EXIT_FAILURE);
	}

	/* make sure pages are actually mapped */
	memset(memory, 0x55, amount);

	printf("Wasting %llu bytes of memory at %p...\n", (unsigned long long)amount, (void*)memory);
	printf("Press enter to stop wasting memory");
	fflush(stdout);

	getchar();
	free(memory);

	return (EXIT_SUCCESS);
}

static size_t
compute_amount(const char *numstr)
{
	unsigned long long size;
	static unsigned long long sizes[] = {
		1000ULL, /* K */
		1000000ULL, /* M */
		1000000000ULL, /* G */
		1000000000000ULL, /* T */
		1000000000000000ULL, /* P */
		1000000000000000000ULL, /* E */
		1ULL << 10, /* k */
		1ULL << 20, /* m */
		1ULL << 30, /* g */
		1ULL << 40, /* t */
		1ULL << 50, /* p */
		1ULL << 60, /* e */
		1ULL, /* no suffix, i.e. \0 */
	};

	const char *sizestr = "KMGTPEkmgtpe", *endptr, *suffix;

	if (!isdigit(numstr[0])) {
		fprintf(stderr, "%s is not a number!\n", numstr);
		exit(EXIT_FAILURE);
	}

	errno = 0;
	size = strtoull(numstr, (char**)&endptr, 10);
	if (endptr[0] != '\0' && endptr[1] != '\0') {
		fprintf(stderr, "unrecognized suffix %s\n", endptr);
		exit(EXIT_FAILURE);
	}

	if (errno == ERANGE) {
		fprintf(stderr, "%s is too much memory!\n", numstr);
		exit(EXIT_FAILURE);
	}

	/* attempt to parse suffix */
	suffix = strchr(sizestr, endptr[0]);
	if (suffix == NULL) {
		fprintf(stderr, "unrecognized suffix %s\n", endptr);
		exit(EXIT_FAILURE);
	}

	/* check for overflow */
	if (size > ULLONG_MAX / sizes[suffix - sizestr] || size * sizes[suffix - sizestr] > (size_t)-1) {
		fprintf(stderr, "%s is too much memory!\n", numstr);
		exit(EXIT_FAILURE);
	}


	return (size * sizes[suffix - sizestr]);
}