From 3983e7f35d5e2a839ebd6423843366f2d19cead8 Mon Sep 17 00:00:00 2001
From: Intel A80486DX2-66 <larry.holst@disroot.org>
Date: Fri, 8 Mar 2024 14:56:35 +0300
Subject: [PATCH] C: add cpuid_vendor_id.mod.c

---
 c-programming/.gitignore                |  1 +
 c-programming/sys/cpuid_vendor_id.mod.c | 82 +++++++++++++++++++++++++
 2 files changed, 83 insertions(+)
 create mode 100644 c-programming/sys/cpuid_vendor_id.mod.c

diff --git a/c-programming/.gitignore b/c-programming/.gitignore
index f3dbb58..522dab0 100644
--- a/c-programming/.gitignore
+++ b/c-programming/.gitignore
@@ -53,3 +53,4 @@
 
 # Custom
 **/*.tmp
+!**/*.mod.c
diff --git a/c-programming/sys/cpuid_vendor_id.mod.c b/c-programming/sys/cpuid_vendor_id.mod.c
new file mode 100644
index 0000000..9f9851d
--- /dev/null
+++ b/c-programming/sys/cpuid_vendor_id.mod.c
@@ -0,0 +1,82 @@
+/*
+ * 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: Creative Commons Zero 1.0 Universal
+ */
+
+#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;
+}