/*
 * cpuid_vendor_id.mod.c
 *
 * The file is a modified version of a gist "cpuid_vendor_id.c" by leiless:
 * https://gist.github.com/leiless/8b8603ae31c00fe38d2e97d94462a5a5
 * (revision 73830d4b10090dcf6748cc60a0aacee252cd9e9d2dd54549aa7b995321380091)
 *
 * The following license information applies for the modifications:
 *     Author: Intel A80486DX2-66
 *     License: Unlicense
 */

#if !(defined(__amd64__) || defined(__amd64) || defined(__x86_64__) || \
      defined(__x86_64) || defined(_M_X64) || defined(_M_AMD64) || \
      defined(__i386) || defined(__i386__) || defined(__IA32__) || \
      defined(_M_I86) || defined(_M_IX86) || defined(__X86__) || defined(_X86_))
# error "This code isn't supposed to work on non-x86 CPUs."
#endif

#include <stdio.h>

#ifdef _WIN32
#include <intrin.h> // __cpuid()
#endif

typedef unsigned int cpuid_t[4];

#define EAX 0
#define EBX 1
#define ECX 2
#define EDX 3

// https://elixir.bootlin.com/linux/latest/source/arch/x86/include/asm/
// processor.h#L216
//
// https://stackoverflow.com/questions/6491566/getting-the-machine-serial
// -number-and-cpu-id-using-c-c-in-linux
//
// https://stackoverflow.com/questions/1666093/cpuid-implementations-in-c
static inline void native_cpuid(unsigned int function_id, cpuid_t r) {
#ifdef _WIN32
	__cpuid((int *) r, (int) function_id);
#else
	r[EAX] = function_id;
	r[ECX] = 0;

	// NOTE:XXX: Register ECX is often an input as well as an output
	asm volatile("cpuid"
		: "=a" (r[EAX]),
		  "=b" (r[EBX]),
		  "=c" (r[ECX]),
		  "=d" (r[EDX])
		: "0" (r[EAX]), "2" (r[ECX])
		: "memory");
#endif
}

#define VENDOR_ID_LEN 13

/*
 * FIXME: you have to make sure the vendor argument is at least lengthed
 * VENDOR_ID_LEN
 */
static inline void cpuid_vendor_id(char vendor[VENDOR_ID_LEN]) {
	// Always initialize the result in case of buggy CPU (like ES/QS CPUs)
	cpuid_t v;
	native_cpuid(0, v);

	// https://learn.microsoft.com/en-us/cpp/intrinsics/cpuid-cpuidex
	// ?view=msvc-170#example
	((unsigned int *) vendor)[0] = v[EBX];
	((unsigned int *) vendor)[1] = v[EDX];
	((unsigned int *) vendor)[2] = v[ECX];
	vendor[VENDOR_ID_LEN - 1] = '\0';
}

int main(void) {
	char vendor_string[VENDOR_ID_LEN];
	cpuid_vendor_id(vendor_string);
	printf("CPU Vendor ID: '%s'\n", vendor_string);
	return 0;
}