/*
 * safe_mem.h
 *
 * A header-only library (macro collection) for safer memory management.
 *
 * NOTE: Declare macro SAFE_MEM_OLD_BSD when compiling if you're using OpenBSD
 * version earlier than 5.5 or FreeBSD version earlier than 11.0.
 *
 * NOTE: See https://git.savannah.gnu.org/gitweb/?p=gnulib.git;a=blob_plain;
 * f=lib/memset_explicit.c;hb=refs/heads/stable-202301
 *
 * Author: Intel A80486DX2-66
 * License: Creative Commons Zero 1.0 Universal
 */

#ifndef _SAFE_MEM_H
#define _SAFE_MEM_H

#define __STDC_WANT_LIB_EXT1__ 1
#include <stdlib.h>

typedef unsigned char byte;

#define SAFE_FREE_ERROR_HOOK /* user-defined */

#define safe_free(ptr) do {                                                   \
    /* prevents NULL-freeing and double freeing */                            \
    if (ptr != NULL) {                                                        \
        free(ptr);                                                            \
        ptr = NULL;                                                           \
    } else { SAFE_FREE_ERROR_HOOK; }                                          \
} while (0)

#define precise_malloc(nmemb, size)                                           \
    /* prevents incorrect casting */                                          \
    malloc((size_t) (nmemb) * (size_t) (size))

/* secure_erase(dest, count): erases memory explicitly */
#if (defined(__OpenBSD__) || defined(__FreeBSD__)) && !defined(SAFE_MEM_OLD_BSD)
# define NO_SECURE_ERASE_WARRANTY 0
# define SECURE_ERASE_WARRANTY "OpenBSD/FreeBSD: explicit_bzero"

# include <strings.h>
# define secure_erase explicit_bzero
#elif defined(_WIN32)
# define NO_SECURE_ERASE_WARRANTY 0
# define SECURE_ERASE_WARRANTY "Microsoft Windows: SecureZeroMemory"

# include <windows.h>
# define secure_erase SecureZeroMemory
#elif __STDC_LIB_EXT1__
# define NO_SECURE_ERASE_WARRANTY 0
# define SECURE_ERASE_WARRANTY "C11+: memset_s"

# include <string.h>
# define secure_erase(dest, count) memset_s((dest), (count), 0, (count))
#else
# define NO_SECURE_ERASE_WARRANTY 1

# include <stdint.h>

# define secure_erase(dest, count) do {                                       \
    uintptr_t max = (uintptr_t) ((count) / sizeof(byte));                     \
    for (size_t i = 0; i < max; i++)                                          \
        *((byte*) (dest) + i) = 0;                                            \
} while (0)
#endif

#endif /* _SAFE_MEM_H */