/*

 * random_seed.c

 *

 * Copyright (c) 2013 Metaparadigm Pte. Ltd.

 * Michael Clark <michael@metaparadigm.com>

 *

 * This library is free software; you can redistribute it and/or modify

 * it under the terms of the MIT license. See COPYING for details.

 *

 */

#include "strerror_override.h"

#include <stdio.h>

#include "config.h"

#include "random_seed.h"

#define DEBUG_SEED(s)

#if defined ENABLE_RDRAND

/* cpuid */

#if defined __GNUC__ && (defined __i386__ || defined __x86_64__)

#define HAS_X86_CPUID 1

static void do_cpuid(int regs[], int h)

{

    __asm__ __volatile__(

#if defined __x86_64__

                         "pushq %%rbx;\n"

#else

                         "pushl %%ebx;\n"

#endif

                         "cpuid;\n"

#if defined __x86_64__

                         "popq %%rbx;\n"

#else

                         "popl %%ebx;\n"

#endif

                         : "=a"(regs[0]), [ebx] "=r"(regs[1]), "=c"(regs[2]), "=d"(regs[3])

                         : "a"(h));

}

#elif defined _MSC_VER

#define HAS_X86_CPUID 1

#define do_cpuid __cpuid

#endif

/* has_rdrand */

#if HAS_X86_CPUID

static int has_rdrand()

{

    // CPUID.01H:ECX.RDRAND[bit 30] == 1

    int regs[4];

    do_cpuid(regs, 1);

    return (regs[2] & (1 << 30)) != 0;

}

#endif

/* get_rdrand_seed - GCC x86 and X64 */

#if defined __GNUC__ && (defined __i386__ || defined __x86_64__)

#define HAVE_RDRAND 1

static int get_rdrand_seed()

{

    DEBUG_SEED("get_rdrand_seed");

    int _eax;

    // rdrand eax

    __asm__ __volatile__("1: .byte 0x0F\n"

                         "   .byte 0xC7\n"

                         "   .byte 0xF0\n"

                         "   jnc 1b;\n"

                         : "=a" (_eax));

    return _eax;

}

#endif

#if defined _MSC_VER

#if _MSC_VER >= 1700

#define HAVE_RDRAND 1

/* get_rdrand_seed - Visual Studio 2012 and above */

static int get_rdrand_seed()

{

    DEBUG_SEED("get_rdrand_seed");

    int r;

    while (_rdrand32_step(&r) == 0);

    return r;

}

#elif defined _M_IX86

#define HAVE_RDRAND 1

/* get_rdrand_seed - Visual Studio 2010 and below - x86 only */

static int get_rdrand_seed()

{

	DEBUG_SEED("get_rdrand_seed");

	int _eax;

retry:

	// rdrand eax

	__asm _emit 0x0F __asm _emit 0xC7 __asm _emit 0xF0

	__asm jnc retry

	__asm mov _eax, eax

	return _eax;

}

#endif

#endif

#endif /* defined ENABLE_RDRAND */

/* has_dev_urandom */

#if defined (__APPLE__) || defined(__unix__) || defined(__linux__)

#include <string.h>

#include <fcntl.h>

#include <unistd.h>

#include <stdlib.h>

#include <sys/stat.h>

#define HAVE_DEV_RANDOM 1

static const char *dev_random_file = "/dev/urandom";

static int has_dev_urandom()

{

    struct stat buf;

    if (stat(dev_random_file, &buf)) {

        return 0;

    }

    return ((buf.st_mode & S_IFCHR) != 0);

}

/* get_dev_random_seed */

static int get_dev_random_seed()

{

    DEBUG_SEED("get_dev_random_seed");

    int fd = open(dev_random_file, O_RDONLY);

    if (fd < 0) {

        fprintf(stderr, "error opening %s: %s", dev_random_file, strerror(errno));

        exit(1);

    }

    int r;

    ssize_t nread = read(fd, &r, sizeof(r));

    if (nread != sizeof(r)) {

        fprintf(stderr, "error short read %s: %s", dev_random_file, strerror(errno));

        exit(1);

    }

    close(fd);

    return r;

}

#endif

/* get_cryptgenrandom_seed */

#ifdef WIN32

#define HAVE_CRYPTGENRANDOM 1

#include <windows.h>

#include <wincrypt.h>

#ifndef __GNUC__

#pragma comment(lib, "advapi32.lib")

#endif

static int get_cryptgenrandom_seed()

{

    HCRYPTPROV hProvider = 0;

    int r;

    DEBUG_SEED("get_cryptgenrandom_seed");

    if (!CryptAcquireContextW(&hProvider, 0, 0, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT | CRYPT_SILENT)) {

        fprintf(stderr, "error CryptAcquireContextW");

        exit(1);

    }

    if (!CryptGenRandom(hProvider, sizeof(r), (BYTE*)&r)) {

        fprintf(stderr, "error CryptGenRandom");

        exit(1);

    }

    CryptReleaseContext(hProvider, 0);

    return r;

}

#endif

/* get_time_seed */

#include <time.h>

static int get_time_seed()

{

    DEBUG_SEED("get_time_seed");

    return (int)time(NULL) * 433494437;

}

/* json_c_get_random_seed */

int json_c_get_random_seed()

{

#if HAVE_RDRAND

    if (has_rdrand()) return get_rdrand_seed();

#endif

#if HAVE_DEV_RANDOM

    if (has_dev_urandom()) return get_dev_random_seed();

#endif

#if HAVE_CRYPTGENRANDOM

    return get_cryptgenrandom_seed();

#endif

    return get_time_seed();

}