From 08c97263333bc01b0c7a367ac51c6b30da93e959 Mon Sep 17 00:00:00 2001
From: Aryadev Chavali <aryadev@aryadevchavali.com>
Date: Sun, 28 Apr 2024 20:57:41 +0530
Subject: [PATCH] Fixed bug with converting (h)word to (h)word in terms of
 endian

While it helped with understanding to use unions as a safe way to
access the underlying bits, this shift based mechanism actually makes
more sense at a glance, particularly by utilising WORD_NTH_BYTE
---
 lib/base.c | 56 ++++++------------------------------------------------
 lib/base.h | 21 ++------------------
 lib/inst.c |  4 ++--
 3 files changed, 10 insertions(+), 71 deletions(-)

diff --git a/lib/base.c b/lib/base.c
index 64039ea..2142039 100644
--- a/lib/base.c
+++ b/lib/base.c
@@ -14,60 +14,16 @@
 
 #include <string.h>
 
-union hword_pun
+hword_t hword_byteswap(const hword_t w)
 {
-  hword_t h;
-  byte_t bytes[HWORD_SIZE];
-};
-
-union word_pun
-{
-  word_t h;
-  byte_t bytes[WORD_SIZE];
-};
-
-hword_t hword_htobc(hword_t w)
-{
-  if (LITTLE_ENDIAN)
-    return w;
-  union hword_pun x = {w};
-  union hword_pun y = {0};
-  for (size_t i = 0, j = HWORD_SIZE; i < HWORD_SIZE; ++i, --j)
-    y.bytes[j - 1] = x.bytes[i];
-  return y.h;
+  return WORD_NTH_BYTE(w, 3) | (WORD_NTH_BYTE(w, 2) << 8) |
+         (WORD_NTH_BYTE(w, 1) << 16) | (WORD_NTH_BYTE(w, 0) << 24);
 }
 
-hword_t hword_bctoh(hword_t w)
+word_t word_byteswap(const word_t w)
 {
-  if (LITTLE_ENDIAN)
-    return w;
-  union hword_pun x = {w};
-  union hword_pun y = {0};
-  for (size_t i = 0, j = HWORD_SIZE; i < HWORD_SIZE; ++i, --j)
-    y.bytes[j - 1] = x.bytes[i];
-  return y.h;
-}
-
-word_t word_htobc(word_t w)
-{
-  if (LITTLE_ENDIAN)
-    return w;
-  union word_pun x = {w};
-  union word_pun y = {0};
-  for (size_t i = 0, j = WORD_SIZE; i < WORD_SIZE; ++i, --j)
-    y.bytes[j - 1] = x.bytes[i];
-  return y.h;
-}
-
-word_t word_bctoh(word_t w)
-{
-  if (LITTLE_ENDIAN)
-    return w;
-  union word_pun x = {w};
-  union word_pun y = {0};
-  for (size_t i = 0, j = WORD_SIZE; i < WORD_SIZE; ++i, --j)
-    y.bytes[j - 1] = x.bytes[i];
-  return y.h;
+  return ((word_t)(hword_byteswap(WORD_NTH_HWORD(w, 0))) << 32) |
+         hword_byteswap(WORD_NTH_HWORD(w, 1));
 }
 
 hword_t convert_bytes_to_hword(const byte_t *bytes)
diff --git a/lib/base.h b/lib/base.h
index c68673b..22d9a11 100644
--- a/lib/base.h
+++ b/lib/base.h
@@ -166,25 +166,8 @@ word_t convert_bytes_to_word(const byte_t *);
 */
 void convert_word_to_bytes(const word_t w, byte_t *buffer);
 
-/**
-   @brief Convert a half word into bytecode format (little endian)
-*/
-hword_t hword_htobc(const hword_t);
+hword_t hword_byteswap(const hword_t h);
 
-/**
-   @brief Convert a half word in bytecode format (little endian) to
-   host format
-*/
-hword_t hword_bctoh(const hword_t);
-
-/**
-   @brief Convert a word into bytecode format (little endian)
-*/
-word_t word_htobc(const word_t);
-
-/**
-   @brief Convert a word in bytecode format (little endian) to host format
-*/
-word_t word_bctoh(const word_t);
+word_t word_byteswap(const word_t w);
 
 #endif
diff --git a/lib/inst.c b/lib/inst.c
index eda2fa0..b41029a 100644
--- a/lib/inst.c
+++ b/lib/inst.c
@@ -431,9 +431,9 @@ size_t prog_write_bytecode(prog_t program, byte_t *bytes, size_t size_bytes)
   if (size_bytes < PROG_HEADER_SIZE || prog_bytecode_size(program) < size_bytes)
     return 0;
   // Write program header i.e. the start and count
-  word_t start = word_htobc(program.start_address);
+  word_t start = word_byteswap(program.start_address);
   *(bytes++)   = start;
-  word_t count = word_htobc(program.count);
+  word_t count = word_byteswap(program.count);
   *(bytes++)   = count;
 
   // Write instructions