From 8b84163c5680f3c88f30e2eaba99fb19a024e5a9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Felix=20Quei=C3=9Fner?= <git@mq32.de>
Date: Thu, 19 May 2016 13:19:38 +0200
Subject: [PATCH] Adds push/pop/peek to VM. Corrects some mistakes in the
 instructions.

---
 prototypes/supervm/instructions.md |  1 +
 prototypes/supervm/main.c          | 32 +++++++++++++++++++++++++--
 prototypes/supervm/vm.c            | 35 +++++++++++++++++++++++++++++-
 prototypes/supervm/vm.h            | 23 ++++++++++++++++++++
 4 files changed, 88 insertions(+), 3 deletions(-)

diff --git a/prototypes/supervm/instructions.md b/prototypes/supervm/instructions.md
index bbca7ce..d45a857 100644
--- a/prototypes/supervm/instructions.md
+++ b/prototypes/supervm/instructions.md
@@ -17,6 +17,7 @@ control stack access or control flow.
 |----------|---------------|-------------------------------------------------|
 |       SP | Stack Pointer | Stores the current 'top' position of the stack. |
 |       BP | Base Pointer  | Stores the current stack frame position.        |
+|       CP | Code Pointer  | Stores the instruction which is executed next.  |
 |       FG | Flag Register | Stores the state of the flags.                  |
 
 ### Stack Pointer
diff --git a/prototypes/supervm/main.c b/prototypes/supervm/main.c
index a136688..0520341 100644
--- a/prototypes/supervm/main.c
+++ b/prototypes/supervm/main.c
@@ -3,10 +3,38 @@
 #include <stdlib.h>
 #include <stdio.h>
 
+Instruction code[] = 
+{
+	{ VM_EXEC_X, VM_EXEC_X, VM_INPUT_ZERO, VM_INPUT_ZERO, VM_CMD_COPY, 0, VM_FLAG_NO, VM_OUTPUT_DISCARD, 0 },
+};
+
+void dump_proc(Process *process)
+{
+	printf("[ ");
+	for(int i = 1; i <= process->stackPointer; i++) {
+		printf("%d ", process->stack[i]);
+	}
+	printf("]\n");
+}
+
+void vm_assert(int assertion, const char *msg)
+{
+	if(assertion != 0)
+		return;
+	printf("Assertion failed: %s\n", msg);
+	exit(1);
+}
+
 int main(int argc, const char **argv)
 {
+	Module module = { code, 1 };
+
+	Process process = { &module, 0, 0, 0, 0 };
+	Process *p = &process;
+	
+	int stillAlive = vm_step_process(p);
+	
+	printf("Process %s.\n", (stillAlive ? "still running" : "terminated"));
 	
-
-
 	return 0;
 }
\ No newline at end of file
diff --git a/prototypes/supervm/vm.c b/prototypes/supervm/vm.c
index d10e0a0..4b29ea8 100644
--- a/prototypes/supervm/vm.c
+++ b/prototypes/supervm/vm.c
@@ -1 +1,34 @@
-#include "vm.h"
\ No newline at end of file
+#include "vm.h"
+
+int vm_step_process(Process *process)
+{
+	vm_assert(process != NULL, "process must not be NULL.");
+	Instruction instr = process->module->code[process->codePointer];
+
+	return 0;
+}
+
+void vm_push(Process *process, uint32_t value)
+{
+	vm_assert(process != NULL, "process must not be NULL.");
+	vm_assert(process->stackPointer < VM_STACKSIZE, "Stack overflow");
+	process->stack[++process->stackPointer] = value;
+}
+
+uint32_t vm_pop(Process *process)
+{
+	vm_assert(process != NULL, "process must not be NULL.");
+	uint32_t psp = process->stackPointer;
+	uint32_t val = process->stack[process->stackPointer--];
+	
+	// Underflow check works because unsigned overflow is defined ;)
+	vm_assert(psp >= process->stackPointer, "Stack underflow");
+	
+	return val;
+}
+
+uint32_t vm_peek(Process *process)
+{
+	vm_assert(process != NULL, "process must not be NULL.");
+	return process->stack[process->stackPointer];
+}
diff --git a/prototypes/supervm/vm.h b/prototypes/supervm/vm.h
index c7e8fc1..b77f06d 100644
--- a/prototypes/supervm/vm.h
+++ b/prototypes/supervm/vm.h
@@ -72,8 +72,16 @@ typedef struct
 _Static_assert(sizeof(Instruction) == 8, "Instruction must be 8 bytes large.");
 _Static_assert(offsetof(Instruction, argument) == 4, "Argument must be  must be 8 bytes large.");
 
+typedef struct
+{
+	Instruction *code;
+	uint32_t length;
+} Module;
+
 typedef struct 
 {
+	Module *module;
+	
 	uint32_t codePointer;
 	uint32_t stackPointer;
 	uint32_t basePointer;
@@ -82,8 +90,23 @@ typedef struct
 	uint32_t stack[VM_STACKSIZE];
 } Process;
 
+/**
+ * @brief Steps a given process.
+ *
+ * Executes a single instruction and processes input and output.
+ *
+ * @param process The process to be stepped.
+ * @returns 1 if the process is still running or 0 if the process is terminated.
+ */
+int vm_step_process(Process *process);
 
+void vm_push(Process *process, uint32_t value);
 
+uint32_t vm_pop(Process *process);
+
+uint32_t vm_peek(Process *process);
+
+void vm_assert(int assertion, const char *msg);
 
 #if defined(__cplusplus)
 }