From cbad8aabbc82efbe7a49572a2da74224ae9c9f85 Mon Sep 17 00:00:00 2001
From: mrb0nk500 <b0nk@b0nk.xyz>
Date: Sun, 1 Dec 2019 17:40:41 -0500
Subject: Added the ability to disable the prefix byte.

Any instructions that either have a register size of
8 bits, use implied addressing, or branch can save a
byte by disabling the prefix byte.

It does this by checking if the first three bits are
all set to 1.
If true, then it will treat it as a prefix
byte, otherwise, it will treat it as an opcode.
---
 asmmon.c | 89 ++++++++++++++++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 70 insertions(+), 19 deletions(-)

(limited to 'asmmon.c')

diff --git a/asmmon.c b/asmmon.c
index fd7c636..1a41214 100644
--- a/asmmon.c
+++ b/asmmon.c
@@ -103,7 +103,7 @@ int asmmon() {
 		char *cmd;
 		char *tmp = malloc(sizeof(char *)*128);
 		size_t size;
-		done &= ~6;
+		done &= ~14;
 		getline(&buf, &size, stdin);
 		cmd = strtok_r(buf, "\n", &tmp);
 		if (cmd != NULL) {
@@ -213,28 +213,79 @@ int asmmon() {
 						}
 					}
 				}
-				if (postfix != NULL && !(done & 6)) {
-					if (strcasecmp(postfix, "w") == 0) {
-						addr[address++] = 1;
-					} else if (strcasecmp(postfix, "d") == 0) {
-						addr[address++] = 2;
-					} else if (strcasecmp(postfix, "q") == 0) {
-						addr[address++] = 3;
-					} else {
-						addr[address++] = 0;
-					}
-				} else if (postfix == NULL && !(done & 6)) {
-					addr[address++] = 0;
-				}
 				if (ins != NULL && !(done & 6)) {
 					uint8_t i;
 					for (i = 0; i < 77; i++) {
 						if (strcasecmp(opcodes[i].mnemonic, ins) == 0) {
+							if (addrmode == 0 && (opcodes[i].impl || opcodes[i].impl == CPS)) {
+								done |= 8;
+							} else if (addrmode == 1) {
+								switch (opcodes[i].imm) {
+									case PHP:
+									case PHA:
+									case PHY:
+									case PHX:
+									case PLP:
+									case PLA:
+									case PLY:
+									case PLX:
+									case STT:
+									case LSL:
+									case LSR:
+									case ROL:
+									case ROR:
+									case ENT:
+										done |= 8;
+										break;
+								}
+							} else {
+								if (strcasecmp(ins, "JMP") == 0)
+									done |=8;
+								if (strcasecmp(ins, "JSR") == 0)
+									done |=8;
+								if (strcasecmp(ins, "JSL") == 0)
+									done |=8;
+								if (strcasecmp(ins, "INC") == 0)
+									done |=8;
+								if (strcasecmp(ins, "BPO") == 0)
+									done |=8;
+								if (strcasecmp(ins, "BNG") == 0)
+									done |=8;
+								if (strcasecmp(ins, "BCS") == 0)
+									done |=8;
+								if (strcasecmp(ins, "BCC") == 0)
+									done |=8;
+								if (strcasecmp(ins, "BEQ") == 0)
+									done |=8;
+								if (strcasecmp(ins, "BNE") == 0)
+									done |=8;
+								if (strcasecmp(ins, "BVS") == 0)
+									done |=8;
+								if (strcasecmp(ins, "BVC") == 0)
+									done |=8;
+							}
 							op = opcodes[i];
 							break;
 						}
 					}
-					uint8_t r = addr[address-1] & 3;
+					if (postfix != NULL && !(done & 8)) {
+						if (strcasecmp(postfix, "w") == 0) {
+							addr[address++] = 0x17;
+						} else if (strcasecmp(postfix, "d") == 0) {
+							addr[address++] = 0x27;
+						} else if (strcasecmp(postfix, "q") == 0) {
+							addr[address++] = 0x37;
+						} else {
+							done |=8;
+						}
+					} else if (postfix == NULL && !(done & 8)) {
+							done |=8;
+					}
+					uint8_t r;
+					if (!(done & 8))
+						r = addr[address-1];
+					else
+						r = 0;
 					switch (addrmode) {
 						case 0:
 							if (op.impl || op.impl == CPS) {
@@ -266,18 +317,18 @@ int asmmon() {
 										break;
 									default:
 										addr[address] = value & 0xFF;
-										if (r & 1)
+										if (r & 0x10)
                 	        	        					addr[address+1] = value >> 8;
-										if (r & 2)
+										if (r & 0x20)
                 	        	        					addr[address+2] = value >> 16;
                 	        	        					addr[address+3] = value >> 24;
-										if (r & 3)
+										if (r & 0x30)
                 	        	        					addr[address+4] = value >> 32;
                 	        	        					addr[address+5] = value >> 40;
                 	        	        					addr[address+6] = value >> 48;
                 	        	        					addr[address+7] = value >> 56;
 
-										address+=(1 << (r & 3));
+										address+=(1 << ((r & 0x30) >> 4));
 										break;
 
 								}
-- 
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