From d4733b7be77acd90d1d60e10d6381f52cb76ce58 Mon Sep 17 00:00:00 2001
From: Abdelrahman Said <said.abdelrahman89@gmail.com>
Date: Sun, 5 Mar 2023 13:58:12 +0000
Subject: [PATCH] Updated decode_register to use flat array instead of branches
---
8086_assembly_01/dasm.cpp | 77 +++++++++------------------------------
1 file changed, 18 insertions(+), 59 deletions(-)
diff --git a/8086_assembly_01/dasm.cpp b/8086_assembly_01/dasm.cpp
index 6695545..34b9ff2 100644
--- a/8086_assembly_01/dasm.cpp
+++ b/8086_assembly_01/dasm.cpp
@@ -96,64 +96,23 @@ uint16_t decode_mode(uint16_t instruction) {
}
void decode_register(uint16_t instruction, bool word, char *dest) {
- uint16_t reg_mask = 0x07;
+ static uint16_t reg_mask = 0x07;
- switch (instruction & reg_mask) {
- case 0x00:
- if (word) {
- strcpy(dest, "ax");
- } else {
- strcpy(dest, "al");
- }
- break;
- case 0x01:
- if (word) {
- strcpy(dest, "cx");
- } else {
- strcpy(dest, "cl");
- }
- break;
- case 0x02:
- if (word) {
- strcpy(dest, "dx");
- } else {
- strcpy(dest, "dl");
- }
- break;
- case 0x03:
- if (word) {
- strcpy(dest, "bx");
- } else {
- strcpy(dest, "bl");
- }
- break;
- case 0x04:
- if (word) {
- strcpy(dest, "sp");
- } else {
- strcpy(dest, "ah");
- }
- break;
- case 0x05:
- if (word) {
- strcpy(dest, "bp");
- } else {
- strcpy(dest, "ch");
- }
- break;
- case 0x06:
- if (word) {
- strcpy(dest, "si");
- } else {
- strcpy(dest, "dh");
- }
- break;
- case 0x07:
- if (word) {
- strcpy(dest, "di");
- } else {
- strcpy(dest, "bh");
- }
- break;
- }
+ // clang-format off
+ static const char *table[16] = {
+ "al", "ax",
+ "cl", "cx",
+ "dl", "dx",
+ "bl", "bx",
+ "ah", "sp",
+ "ch", "bp",
+ "dh", "si",
+ "bh", "di"
+ };
+ // clang-format on
+
+ uint16_t offset = instruction & reg_mask;
+
+ // Multiply offset by 2 since each row has 2 columns
+ strcpy(dest, table[offset * 2 + (uint16_t)word]);
}