From 7854c6d1c129f1979434514f4716d89752608288 Mon Sep 17 00:00:00 2001
From: ubq323 <ubq323@ubq323.website>
Date: Wed, 26 Jun 2024 12:00:12 +0100
Subject: make stackpointer less bad

previously was the length of the stack, ie number of
items above current fp, and so needed to be adjusted
in each call or ret

now it's just an absolute index into the stack, like it always should have been
---
 vm.c | 35 ++++++++++++++++++-----------------
 1 file changed, 18 insertions(+), 17 deletions(-)

(limited to 'vm.c')

diff --git a/vm.c b/vm.c
index 9a69472..a5ffbc6 100644
--- a/vm.c
+++ b/vm.c
@@ -36,17 +36,19 @@ int runvm(State *S) {
 #define RBYTE() (ch->bc.d[th->ip++])
 #define RSHORT() (th->ip += 2, (uint16_t)( ch->bc.d[th->ip-2] | ch->bc.d[th->ip-1] << 8 ))
 
-#define PUSH(v) th->stack[th->fp + th->sp++] = v;
-#define POP()   (th->stack[th->fp + --th->sp])
-#define PEEK()  (th->stack[th->fp + th->sp-1])
+#define PUSH(v) th->stack[th->sp++] = v;
+#define POP()   (th->stack[--th->sp])
+#define PEEK()  (th->stack[th->sp-1])
+// 1 is TOS
+#define PEEKN(n) (th->stack[th->sp-n])
 
 	while (1) {
 		ch = th->ch;
 		if (S->do_trace) {
-			printf("\t[%lu + %lu] : ",th->fp, th->sp);
-			for (int i = 0; i < th->sp; i++) {
+			printf("\t[%lu -> %lu] : ",th->fp, th->sp);
+			for (int i = th->fp; i < th->sp; i++) {
 				printf("(%d) ",i);
-				print_val(th->stack[th->fp + i]);
+				print_val(th->stack[i]);
 				printf(" ; ");
 			}
 			printf("\n%p ",(void *)ch);
@@ -178,25 +180,25 @@ int runvm(State *S) {
 		case OP_FALSE: PUSH(VAL_FALSE); break;
 
 		case OP_CALL: {
+			// nargs + 1 = function and args
 			uint8_t len = RBYTE();
-			th->sp -= len-1;
-			Val callee = POP();
 
+			Val callee = PEEKN(len);
 			if (!IS_FUNC(callee)) {
-				fprintf(stderr, "can only call functions\n");
-				goto done;
+				fprintf(stderr,"can only call functions");
+				exit(1);
 			}
 			ObjFunc *func = AS_FUNC(callee);
 
 			StackFrame *sf = &th->rstack[th->rsp++];
-			sf->ch = th->ch;
 			sf->ip = th->ip;
+			sf->ch = th->ch;
 			sf->fp = th->fp;
 
-			th->ch = &func->ch;
 			th->ip = 0;
-			th->fp = th->sp;
-			th->sp = len;
+			th->ch = &func->ch;
+			th->fp = th->sp - len;
+
 			break;
 		}
 
@@ -210,11 +212,10 @@ int runvm(State *S) {
 
 		case OP_RET: {
 			StackFrame *sf = &th->rstack[--th->rsp]; 
-			size_t orig_fp = th->fp;
-			th->ch = sf->ch;
+
 			th->ip = sf->ip;
+			th->ch = sf->ch;
 			th->fp = sf->fp;
-			th->sp += (orig_fp - th->fp);
 			break;
 		}
 		case OP_HALT:
-- 
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